水稻幼苗特性与籽粒大小关系的分子检测

水稻( Oryza sativa L.)幼苗特性如叶的发生、叶绿素含量、植株高度等对早期生长是重要的,与籽粒大小相联系.以水稻珍汕97A和明恢63组合的重组自交系群体为材料,对5个幼苗特性性状和籽粒大小进行了数量性状基因定位(QTL),目的在于从遗传水平探求幼苗特性与籽粒大小的内在关系.对叶绿素a、总叶绿素含量、第二片叶长、第三片叶长、幼苗高度、粒重分别检测到2、1、5、4、4、9个QTLs.结果揭示4个幼苗特性性状的QTL和4个籽粒大小的QTL位点分别定位在4个相似区域 (G359-RG532、C567-RG236、RZ403-R19和C371-C405a),表明幼苗特性性状与籽粒大小间的紧密关系,也显示控制籽粒大小的几个染色体区域对幼苗特性性状没有影响,这意味着通过标记辅助选择改良幼苗活力但并不增加粒重是可能的.     

水稻幼苗特性与籽粒大小关系的分子检测

水稻 (OryzasativaL .)幼苗特性如叶的发生、叶绿素含量、植株高度等对早期生长是重要的 ,与籽粒大小相联系。以水稻珍汕 97A和明恢 6 3组合的重组自交系群体为材料 ,对 5个幼苗特性性状和籽粒大小进行了数量性状基因定位 (QTL) ,目的在于从遗传水平探求幼苗特性与籽粒大小的内在关系。对叶绿素a、总叶绿素含量、第二片叶长、第三片叶长、幼苗高度、粒重分别检测到 2、1、5、4、4、9个QTLs。结果揭示 4个幼苗特性性状的QTL和 4个籽粒大小的QTL位点分别定位在 4个相似区域 (G35 9_RG5 32、C5 6 7_RG2 36、RZ4 0 3_R1 9和C371_C4 0 5a) ,表明幼苗特性性状与籽粒大小间的紧密关系 ,也显示控制籽粒大小的几个染色体区域对幼苗特性性状没有影响 ,这意味着通过标记辅助选择改良幼苗活力但并不增加粒重是可能的     

Nitrogen Stress Affects the Turnover and Size of Nitrogen Pools Supplying Leaf Growth in a Grass

The effect of nitrogen (N) stress on the pool system supplying currently assimilated and (re)mobilized N for leaf growth of a grass was explored by dynamic ¹⁵N labeling, assessment of total and labeled N import into leaf growth zones, and compartmental analysis of the label import data. Perennial ryegrass (Lolium perenne) plants, grown with low or high levels of N fertilization, were labeled with ¹⁵NO₃⁻/¹⁴NO₃⁻ from 2 h to more than 20 d. In both treatments, the tracer time course in N imported into the growth zones fitted a two-pool model (r² > 0.99). This consisted of a “substrate pool,” which received N from current uptake and supplied the growth zone, and a recycling/mobilizing “store,” which exchanged with the substrate pool. N deficiency halved the leaf elongation rate, decreased N import into the growth zone, lengthened the delay between tracer uptake and its arrival in the growth zone (2.2 h versus 0.9 h), slowed the turnover of the substrate pool (half-life of 3.2 h versus 0.6 h), and increased its size (12.4 μg versus 5.9 μg). The store contained the equivalent of approximately 10 times (low N) and approximately five times (high N) the total daily N import into the growth zone. Its turnover agreed with that of protein turnover. Remarkably, the relative contribution of mobilization to leaf growth was large and similar (approximately 45%) in both treatments. We conclude that turnover and size of the substrate pool are related to the sink strength of the growth zone, whereas the contribution of the store is influenced by partitioning between sinks.This article examines the nitrogen (N) supply system of growing grass leaves, and it investigates how functional and kinetic properties of this system are affected by N stress. The N supply of growing leaves is a dominant target of whole-plant N metabolism. This is primarily related to the high N demand of the photosynthetic apparatus and the related metabolic machinery of new leaves (Evans, 1989; Makino and Osmond, 1991; Grindlay, 1997; Lemaire, 1997; Wright et al., 2004; Johnson et al., 2010; Maire et al., 2012). The N supply system, as defined here, is an integral part of the whole plant: it includes all N compounds that supply leaf growth. Hence, it integrates all events between the uptake of N from the environment (source), intermediate uses in other processes of plant N metabolism, and the eventual delivery to the leaf growth zone (sink; Fig. 1). N that does not ultimately serve leaf growth is not included in this system; all N that serves leaf growth is included, irrespective of its localization in the plant. Conceptually, two distinct sources supply N for leaf growth: N from current uptake and assimilation that is directly transferred to the growing leaf (“directly transferred N”) and N from turnover/redistribution of organic compounds (“mobilized N”).Open in a separate windowFigure 1.Schematic representation of N fluxes in the leaf growth zone and in the N supply system of leaf growth in a grass plant. A, Scheme of a growing leaf, with its growth zone (including zones of cell division, expansion, and maturation) and recently produced tissue (RPT). N import (I; μg h⁻¹) into the growth zone is mostly in the form of amino acids. Inside the growth zone, the nitrogenous substrate is used in new tissue construction. Then, N export (E; μg h⁻¹) is in the form of newly formed, fully expanded nitrogenous tissue (tissue-bound export with RPT) and is calculated as leaf elongation rate (L_ER; mm h⁻¹) times the lineal density of N in RPT (ρ; μg mm⁻¹): E = L_ER × ρ (Lattanzi et al., 2004). In a physiological steady state, import equals export (I = E) and the N content of the growth zone (G; μg [not shown]) is constant. Labeled N import into the growth zone (I_lab) commences shortly after labeling of the nutrient solution with ¹⁵N. The labeled N content of the growth zone (G_lab; μg) increases over time (dG_lab/dt) until it eventually reaches isotopic saturation (Fig. 2B). Similarly, the lineal density of labeled N in RPT (ρ_lab) increases until it approaches ρ. At any time, the export of labeled N in RPT (E_lab) equals the concurrent ρ_lab × L_ER. The import of labeled N is obtained as I_lab = E_lab + dG_lab/dt (Lattanzi et al., 2005) and considers the increasing label content in the growth zone during labeling. The fraction of labeled N in the import flux (f_{lab I}) is calculated as f_{lab I} = I_lab/I. The time course of f_{lab I} (Fig. 3) reflects the kinetic properties of the N supply system of leaf growth (C). B, Scheme of a vegetative grass plant (reduced to a rooted tiller with three leaves) with leaf growth zone. N import into the growth zone (I) originates from (1) N taken up from the nutrient solution that is transferred directly to the growth zone following assimilation (directly transferred N) and (2) N derived from turnover/redistribution of stores (mobilized N). The store potentially includes proteins in all mature and senescing tissue in the shoot and root of the entire plant. As xylem, phloem, and associated transfer cells/tissue provide for a vascular network that connects all parts of the plant, the mobilized N may principally originate from any plant tissue that exhibits N turnover/mobilization. The fraction of total N uptake that is allocated to the N supply system of the growth zone equals U (see model in C). The fraction of total mobilized N allocated to the growth zone equals M (see model in C). C, Compartmental model of the source-sink system supplying N to the leaf growth zone, as shown by Lattanzi et al. (2005) and used here. Newly absorbed N (U; μg h⁻¹) enters a substrate pool (Q₁); from there, the N is either imported directly into the growth zone (I) or exchanged with a store (Q₂). Q₁ integrates the steps of transport and assimilation that precede the translocation to the growth zone. Q₂ includes all proteins that supply N for leaf growth during their turnover and mobilization. The parameters of the model, including the (relative) size and turnover of pools Q₁ and Q₂, the deposition into the store (D; μg h⁻¹), and the mobilization from the store (M; μg h⁻¹), and the contribution of direct transfer relative to mobilization to the N supply of the growth zone are obtained by fitting the compartmental model to the f_{lab I} data (A) obtained in dynamic ¹⁵N labeling experiments (for details, see “Materials and Methods”). During physiological steady state, the sizes of Q₁ and Q₂ are constant, I = U, and M = D. [See online article for color version of this figure.]Amino acids are the predominant form in which N is supplied for leaf growth in grasses, and incorporation in new leaf tissue occurs mainly in the leaf growth zone (Gastal and Nelson, 1994; Amiard et al., 2004). This is a heterotrophic piece of tissue that includes the zones of cell division and elongation, is located at the base of the leaf, and is encircled by the sheath of the next older leaf (Volenec and Nelson, 1981; MacAdam et al., 1989; Schnyder et al., 1990; Kavanová et al., 2008). As most N is taken up in the form of nitrate but supplied to the growth zone in the form of amino acids, the path of directly transferred N includes a series of metabolic and transport steps. These include transfer to and loading into the xylem, xylem transport and unloading, reduction and ammonium assimilation, cycling through photorespiratory N pools, amino acid synthesis, loading into the phloem, and transport to the growth zone (Hirel and Lea, 2001; Novitskaya et al., 2002; Stitt et al., 2002; Lalonde et al., 2003; Dechorgnat et al., 2011). The time taken to pass through this sequence is unknown at present, as is the effect of N deficiency on that time. Also, it is not known how much N is contained in, and moving through, the different compartments that supply leaf growth with currently assimilated N.At the level of mature organs, mainly leaves, there is considerable knowledge about N turnover and redistribution. Much less is known about the fate of the mobilized N and its actual use in sink tissues like the leaf growth zone. The processes in mature organs are associated with the maintenance metabolism of proteins, organ senescence, and adjustments in leaf protein levels to decreasing irradiance inside growing canopies when leaves become shaded by overtopping newer ones (Evans, 1993; Vierstra, 1993; Hikosaka et al., 1994; Anten et al., 1995; Hirel et al., 2007; Jansson and Thomas, 2008; Moreau et al., 2012). N mobilization in shaded leaves supports the optimization of photosynthetic N use efficiency at plant and canopy scale (Field, 1983; Evans, 1993; Anten et al., 1995), it reduces the respiratory burden of protein maintenance costs (Dewar et al., 1998; Amthor, 2000; Cannell and Thornley, 2000), and it provides a mechanism for the conservation of the most frequently growth-limiting nutrient (Aerts, 1996). Mobilization of N involves protein turnover and net degradation (Huffaker and Peterson, 1974), redistribution in the form of amino acids (Simpson and Dalling, 1981; Simpson et al., 1983; Hörtensteiner and Feller, 2002), and (at least) some of the mobilized N is supplied to new leaf growth (Lattanzi et al., 2005).N fertilizer supply has multiple direct and indirect effects on plant N metabolism (Stitt et al., 2002; Schlüter et al., 2012). In particular, it modifies the N content of newly produced leaves, leaf longevity/senescence, and the dynamics of light distribution inside expanding canopies (Evans, 1983, 1989; Lötscher et al., 2003; Moreau et al., 2012). Thus, N fertilization influences the availability of recyclable N. At the same time, it augments the availability of directly transferable N to leaf growth. The net effect of these factors on the importance of mobilized versus directly transferred N substrate for leaf growth is not known. Also, it is unknown how N fertilization influences the functional characteristics of the N supply system, such as the size and turnover of its component pools.The assessment of the importance of directly transferred versus mobilized N for leaf growth requires studies at the sink end of the system (i.e. investigations of the N import flux into the leaf growth zone). Directly transferred N and mobilized N can be distinguished on the basis of their residence time in the plant, the time between uptake from the environment and import into the leaf growth zone: direct transfer involves a short residence time (fast transfer), whereas mobilized N resides much longer in the plant before it is delivered to the growth zone (slow transfer; De Visser et al., 1997; Lattanzi et al., 2005). Such studies require dynamic labeling of the N taken up by the plant (Schnyder and de Visser, 1999) and monitoring of the rate and isotopic composition/label content of N import into the leaf growth zone (Lattanzi et al., 2005). For grass plants in a physiological steady state, N import and the isotopic composition of the imported N are calculated from the leaf elongation rate and the lineal density of N in newly formed tissue (Fig. 1A; Lattanzi et al., 2004) and the change of tracer content in the leaf growth zone and recently produced leaf tissue over time (Lattanzi et al., 2005). Such data reveal the temporal change of the fraction of labeled N in the N import flux (f_{lab I}), which then can be used to characterize the N supply system of leaf growth via compartmental modeling. So far, there is only one study that has partially characterized this system (Lattanzi et al., 2005): this work was conducted with a C₃ grass, perennial ryegrass (Lolium perenne), and a C₄ grass, Paspalum dilatatum, growing in mixed stands and indicated that two interconnected N pools supplied the leaf growth zone in both species: a “substrate pool” (Q₁), which provided a direct route for newly absorbed and assimilated N import into the leaf growth zone (directly transferred N), and a mobilizing “store” (Q₂), which supplied N to the leaf growth zone via the substrate pool (Fig. 1C). The relative contribution of mobilization from the store was least important in the fast-growing, dominant individuals and most important in subordinate, shaded individuals. That work did not address the role of N deficiency, and the limited short-term resolution of the study (labeling intervals of 24 h or greater) precluded an analysis of the fast-moving parts of the system.Accordingly, this work addresses the following questions. How does N deficiency influence the substrate supply system of the leaf growth sink in terms of the number, size, and turnover (half-life) of its kinetically distinct pools? How does N deficiency affect the relationship between directly transferred and mobilized N for leaf growth? And what additional insight on the compartmental structure of the supply system is obtained when the short-term resolution of the analysis is increased by 1 order of magnitude? The work was performed with vegetative plants of perennial ryegrass grown in constant conditions with either a low (1.0 mm; termed low N) or high (7.5 mm; high N) nitrate concentration in the nutrient solution. In both treatments, a large number of plants were dynamically labeled with ¹⁵N over a wide range of time intervals (2 h to more than 20 d). The import of total N and ¹⁵N tracer into growth zones was estimated at the end of each labeling interval. Tracer data were analyzed with compartmental models following principles detailed by Lattanzi et al. (2005, 2012) and Lehmeier et al. (2008) to address the specific questions. Previous articles reported on root and shoot respiration (Lehmeier et al., 2010) and cell division and expansion in leaf growth zones (Kavanová et al., 2008) in the same experiment.     

椭圆分布函数模拟水稻冠层叶倾角分布

利用双参数椭圆分布函数,结合Powell法寻优,对水稻冠层叶倾角分布进行模拟,并与实测值进行比较,取得了较为满意的结果。     

Mutation in Mg-Protoporphyrin IX Monomethyl Ester Cyclase Causes Yellow and Spotted Leaf Phenotype in Rice

Plant Molecular Biology Reporter - Mg-protoporphyrin IX monomethyl ester cyclase (MPEC) plays an essential role in chlorophyll biosynthesis. Further study on the key enzyme will provide us more...     

6-BA对红掌组织培养中红叶变异的影响

以红掌盆栽品种‘Avo-Gloria’为试材,以MS＋0.2mg·L^-12,4-D为基本培养基,分别在添加1～10mg·L^-16-BA的10种脱分化培养基上,诱导其叶柄外植体产生愈伤组织;再以MS＋2mg·L^-16-BA＋0.2mg·L^-1 NAA为分化培养基诱导分化不定芽;以MS＋0.2mg·L^-1 NAA为生根培养基,从不定芽获得再生植株。结果显示：（1）在MS＋0.2mg·L^-12,4-D＋8～10mg·L^-16-BA的3种脱分化培养基上可产生9%～10%的绿色、质地较硬的愈伤组织;（2）愈伤组织在MS＋2mg·L^-16-BA＋0.2mg·L^-1 NAA的分化培养基上,经6～8次继代培养,可获得3%～7%的不定芽,并可生根长成再生植株;（3）再生植株定植3个月后,有3%～7%植株出现红叶变异,此红叶可终生表现为红色。     

Metabolic Profiling and Physiological Analysis of a Novel Rice Introgression Line with Broad Leaf Size

A rice introgression line, NIL-SS1, and its recurrent parent, Teqing, were used to investigate the influence of the introgression segment on plant growth. The current research showed NIL-SS1 had an increased flag leaf width, total leaf area, spikelet number per panicle and grain yield, but a decreased photosynthetic rate. The metabolite differences in NIL-SS1 and Teqing at different developmental stages were assessed using gas chromatography—mass spectrometry technology. Significant metabolite differences were observed across the different stages. NIL-SS1 increased the plant leaf nitrogen content, and the greatest differences between NIL-SS1 and Teqing occurred at the booting stage. Compared to Teqing, the metabolic phenotype of NIL-SS1 at the booting stage has closer association with those at the flowering stage. The introgression segment induced more active competition for sugars and organic acids (OAs) from leaves to the growing young spikes, which resulted in more spikelet number per plant (SNP). The results indicated the introgression segment could improve rice grain yield by increasing the SNP and total leaf area per plant, which resulted from the higher plant nitrogen content across growth stages and stronger competition for sugars and OAs of young spikes at the booting stage.     

Influence of Seed Size on Exploitation by the Rice Weevil, Sitophilus oryzae

Oviposition decisions and their fitness consequences for the seed parasite Sitophilus oryzae (L.) (Coleoptera: Curculionidae) were investigated. Female S. oryzae lay eggs inside seeds such as wheat [Triticum aestivum (L.)]. Because larvae develop to adult within a single seed, the resources available are determined by the behavior of the female parent and characteristics of the seed in which the egg was deposited. Females were demonstrated to lay more eggs in kernels 20 mg. Females initiated the chewing of oviposition holes in shriveled kernels but were less likely to oviposit in them. Progeny size increased with increasing seed size, but the probability of an adult emerging was not affected. Females accepted large kernels more quickly than small kernels and this contributed to increased oviposition in large kernels. The increase in the number of eggs per kernel appears to result from an increase in number of visits resulting in oviposition rather than an increase in the number of eggs laid during a visit.     

Inflorescence Initiation and Leaf Size in Some Gramineae

The morphology of successive leaves on the flowering shoot wasstudied in species of Glyceria, Lolium, and Triticum. The bladesof successive leaves were progressively longer, eventually reachinga maximum, after which the blades of the last few leaves producedbefore heading were shorter. When the longest leaf blade waselongating, dissection of the shoot apices showed that inflorescenceinitiation was taking place. Epidermal cell measurements inTriticum indicate that differences in blade length are due todifferences in the amount of cell extension. It appears that a correlated change occurs in blade morphologyassociated with the onset of the reproductive state of the shootapex, brought about via changes in the amount of cell extension. A study of the effect of different amounts of low-temperatureand different day-lengths on the relation between inflorescenceinitiation and the production of the longest leaf blade showedthat, under some conditions, this relation can be disturbed.     

Mechanisms Determining Leaf Movement and Leaf Angle in Wheat (Triticum aestivumL.)

All wheat leaves examined showed a downward movement after emergence.There was always a first phase in the movement bringing thelaminae to an inclination of about 60° above a horizontalplane. In some cultivars, the movement continued and a secondphase was observed. Leaf leverage and ear removal affected thissecond phase. The first phase was not affected. Only a partof the deformation in the zone of attachment of the lamina toits sheath responsible for leaf angle was elastic and thereforereversible. Without elastic deformation, most leaves would beoriented above the horizontal.     

On the Relevance and Control of Leaf Angle

Plants can have constitutive leaf angles that are fixed and do not vary much among different growth environments. Several species, however, have the ability to actively adjust their leaf angles. Active leaf repositioning can be functional in avoiding detrimental environmental conditions, such as avoidance of heat stress and complete submergence, or can be, for example, utilized to maximize carbon gain by positioning the leaves relative to the incoming radiation. In recent years, major advances have been made in the understanding of the molecular mechanisms, and the underlying hormonal regulation of a particular type of leaf movement: hyponastic growth. This differential petiole growth-driven upward leaf movement is now relatively well understood in model systems such as Rumex palustris and Arabidopsis thaliana. In the first part of this review we will discuss the functional consequences of leaf orientation for plant performance. Next, we will consider hyponastic growth and describe how exploitation of natural (genetic) variation can be instrumental in studying the relevance and control of leaf positioning.     

The Control of Leaf and Ear Size in Barley

The relative growth rates, growth rates, and final size of tillersand main-shoot leaves, internodes, and ear of a freely tilleringspring barley genotype were measured and compared with thoseof a non-tillering single-gene mutant. Leaf and internode growthand final size were greater in the non-tillering mutant. Thedifferences, it is proposed, arise because of changes in internalcompetition for assimilates brought about by the absence oftillers. There was little difference in ear growth or size,possibly because of abnormalities of ear development, whichresulted in fewer spikelets in the non-tillering genotype.     

The F-Box Protein OsFBK12 Targets OsSAMS1 for Degradation and Affects Pleiotropic Phenotypes,Including Leaf Senescence,in Rice

Leaf senescence is related to the grain-filling rate and grain weight in cereals. Many components involved in senescence regulation at either the genetic or physiological level are known. However, less is known about molecular regulation mechanisms. Here, we report that OsFBK12 (an F-box protein containing a Kelch repeat motif) interacts with S-ADENOSYL-l-METHIONINE SYNTHETASE1 (SAMS1) to regulate leaf senescence and seed size as well as grain number in rice (Oryza sativa). Yeast two-hybrid, pull-down, and bimolecular fluorescence complementation assays indicate that OsFBK12 interacts with Oryza sativa S-PHASE KINASE-ASSOCIATED PROTEIN1-LIKE PROTEIN and with OsSAMS1. Biochemical and physiological data showed that OsFBK12 targets OsSAMS1 for degradation. OsFBK12-RNA interference lines and OsSAMS1 overexpression lines showed increased ethylene levels, while OsFBK12-OX lines and OsSAMS1-RNA interference plants exhibited decreased ethylene. Phenotypically, overexpression of OsFBK12 led to a delay in leaf senescence and germination and increased seed size, whereas knockdown lines of either OsFBK12 or OsSAMS1 promoted the senescence program. Our results suggest that OsFBK12 is involved in the 26S proteasome pathway by interacting with Oryza sativa S-PHASE KINASE-ASSOCIATED PROTEIN1-LIKE PROTEIN and that it targets the substrate OsSAMS1 for degradation, triggering changes in ethylene levels for the regulation of leaf senescence and grain size. These data have potential applications in the molecular breeding of rice.F-box proteins are components of E3 ubiquitin ligase S-PHASE KINASE-ASSOCIATED PROTEIN, CULLIN, F-BOX CONTAINING COMPLEXES (SCFs), which mediate a wide variety of biological processes (Schulman et al., 2000). The N terminus of F-box proteins, which interacts with S-Phase Kinase-Associated Protein1 (Skp1), is conserved. The C terminus generally contains one or several highly variable protein-protein interaction domains, such as Leu-rich repeat, Kelch repeat, tetratricopeptide repeat, or WD40 repeat domains (Jain et al., 2007). Kelch motifs consist of 44 to 56 amino acid residues, with four highly conserved residues, two adjacent Gly residues, and a Tyr and Trp pair separated by about six residues. The presence of Kelch repeats is a unique characteristic of a subset of F-box proteins in plants (Prag and Adams, 2003).F-box proteins target their substances for specific functions. Several key hormone signaling components, including receptors, have been identified as F-box proteins. The TRANSPORT INHIBITOR RESPONSE1 (TIR1) F-box protein acts as an auxin receptor regulating the stability of auxin/indole-3-acetic acid proteins in Arabidopsis (Arabidopsis thaliana; Gray et al., 2001; Zhang et al., 2011). CORONATINE-INSENSITIVE1 is an F-box protein that is a coreceptor with JASMONATE ZIM-DOMAIN PROTEIN1 as a central regulator of jasmonate signaling (Sheard et al., 2010). SNEEZY and SLEEPY1 regulate DELLA through interaction with the DELLA-GIBBERELLIN-INSENSITIVE DWARF1 complex in GA signaling (Dill et al., 2004; Strader et al., 2004). In addition, ETHYLENE-INSENSITIVE2 and ETHYLENE-INSENSITIVE3 are quickly degraded by the F-box proteins ETHANOL TOLERANCE PROTEIN1/ETHANOL TOLERANCE PROTEIN2 and EARLY B-CELL FACTOR1/EARLY B-CELL FACTOR2 during ethylene signaling (Guo and Ecker, 2003; Potuschak et al., 2003; Qiao et al., 2009; Wang et al., 2009a). Only a few F-box proteins containing Kelch motifs (FBKs), however, have been characterized. The FBK proteins ZEITLUPE, FLAVIN-BINDING, KELCH REPEAT, F-BOX1, and LOV KELCH PROTEIN2 are involved in light signaling, flowering, and circadian control via a proteasome-dependent pathway in Arabidopsis (Imaizumi et al., 2005). The rice (Oryza sativa) FBK gene LARGER PANICLE/ERECT PANICLE3 was reported to regulate panicle architecture (Piao et al., 2009) and modulate cytokinin levels through Oryza sativa CYTOKININ OXIDASE2 expression (Li et al., 2011a). However, only a few substances for F-box proteins with specific functions are known in plants. In other words, it is still not clear how F-box proteins mediate plant developmental processes such as leaf senescence and seed size.Leaf senescence and the related ethylene regulation impact grain filling, which is an important determinant of yield, especially in the last stage of maturation in rice. Delayed leaf senescence was reported to be mediated by a nucleus-localized zinc finger protein, Oryza sativa DELAY OF THE ONSET OF SENESCENCE, in rice (Kong et al., 2006). The STAY GREEN RICE gene is involved in regulating pheophorbide a oxygenase that causes alterations in chlorophyll breakdown during senescence (Jiang et al., 2007). Physiologically, the progression of leaf senescence is dependent on ethylene levels, which also regulate grain filling (Wuriyanghan et al., 2009; Agarwal et al., 2012). In plants, it is well established that ethylene is biosynthesized from S-adenosyl-l-methionine (SAM) via 1-aminocyclopropane-1-carboxylic acid (ACC). ACC synthase catalyzes the first step of the biosynthesis by converting S-adenosylmethionine into ACC, and ACC oxidase catalyzes the second step by metabolizing ACC and dioxygen into ethylene. S-Adenosyl-l-methionine synthase (SAMS) is involved in developmental regulation mediated by methylation alterations of DNA and histones in rice (Li et al., 2011b). The physiological function of ethylene in rice is dependent not only on its biosynthesis but also on signal transduction components such as the ETHYLENE-RESPONSE2 receptor (Zhu et al., 2011). However, less is known about how F-box protein regulation is involved in the coordination of senescence progression.Here, we show that a rice F-box gene, OsFBK12, that contains a Kelch repeat domain is involved in the regulation of ethylene-mediated senescence and seed size. Transgenic lines with reduced or increased expression of OsFBK12 showed phenotypes in germination, panicle architecture, and leaf senescence as well as in seed size. Our data suggest that OsFBK12 directly interacts with OsSAMS1 to induce its degradation, which affects ethylene synthesis and histone methylation, leading to pleiotropic phenotypes.     

Rice Fertilization-Independent Endosperm1 Regulates Seed Size under Heat Stress by Controlling Early Endosperm Development

Although heat stress reduces seed size in rice (Oryza sativa), little is known about the molecular mechanisms underlying the observed reduction in seed size and yield. To elucidate the mechanistic basis of heat sensitivity and reduced seed size, we imposed a moderate (34°C) and a high (42°C) heat stress treatment on developing rice seeds during the postfertilization stage. Both stress treatments reduced the final seed size. At a cellular level, the moderate heat stress resulted in precocious endosperm cellularization, whereas severe heat-stressed seeds failed to cellularize. Initiation of endosperm cellularization is a critical developmental transition required for normal seed development, and it is controlled by Polycomb Repressive Complex2 (PRC2) in Arabidopsis (Arabidopsis thaliana). We observed that a member of PRC2 called Fertilization-Independent Endosperm1 (OsFIE1) was sensitive to temperature changes, and its expression was negatively correlated with the duration of the syncytial stage during heat stress. Seeds from plants overexpressing OsFIE1 had reduced seed size and exhibited precocious cellularization. The DNA methylation status and a repressive histone modification of OsFIE1 were observed to be temperature sensitive. Our data suggested that the thermal sensitivity of seed enlargement could partly be caused by altered epigenetic regulation of endosperm development during the transition from the syncytial to the cellularized state.World rice (Oryza sativa) production needs to increase significantly to sustain an increasing population. However, higher average temperatures caused by global warming are predicted to decrease rice yields in many parts of the world, especially Asia. In one study, rice yield was estimated to decrease by 10% for every 1°C rise in minimum growing season temperature (Peng et al., 2004). Comparable yield losses with rising temperatures have been reported for two other major cereal crops: wheat (Triticum spp.) and maize (Zea mays; Wardlaw, 1989; Lobell et al., 2011). Rice, wheat, and maize together are the main sources of calories for most countries (Reynolds et al., 2011). Therefore, it is critical that we understand the agronomic, biological, and economic consequences of high temperature on crop yields.Heat stress during seed development decreases the seed size in many cereals (Nagato and Ebata, 1960; Hunter et al., 1977; Savin et al., 1996) and when coupled with seed number per unit area, determines seed yield. Seed size is largely contributed by the endosperm, a triploid tissue derived from fusion of the sperm cell with the diploid central cell during the double fertilization event. Endosperm development progresses in distinct developmental stages. After fertilization, the endosperm enters the syncytial stage, where triploid nuclei undergo rapid mitotic divisions without cytokinesis, followed by cellularization and finally, differentiation and maturation (Olsen, 2001; Sabelli and Larkins, 2009b). Duration of the syncytial stage and rate of mitotic divisions during this stage are important determinants of seed size (Mizutani et al., 2010). Successful transition from the syncytial to the cellularization stage is critical for normal seed development (Brown et al., 1996).In Arabidopsis (Arabidopsis thaliana), the processes controlling early endosperm development and the transition from syncytial to cellularized stage are associated with the Polycomb Repressive Complex2 (PRC2) genes, which includes Fertilization-Independent Endosperm (FIE), Fertilization-Independent Seed2 (FIS2), Medea (MEA), and Multicopy Suppressor of IRA1 (Guitton and Berger, 2005; Baroux et al., 2006; Huh et al., 2007). The PRC2 complex is involved in gene silencing mediated by a repressive histone modification (H3K27me3; Köhler and Villar, 2008). Loss of function of several of these PRC2 genes results in abnormal endosperm development. A notable phenotype observed in Arabidopsis FIS mutants is endosperm overproliferation and seed failure (Kiyosue et al., 1999; Sørensen et al., 2002). Several endosperm-specific MADS-box genes (such as Pheres1, AGAMOUS-LIKE36 (AGL36), and AGL62 among others) are misregulated in seeds that are deficient in PRC2-encoding genes (Kang et al., 2008; Köhler and Villar, 2008; Walia et al., 2009). A loss-of-function mutation in Arabidopsis AGL62 resulted in precocious cellularization and smaller seeds (Kang et al., 2008). Although the function of the PRC2 complex is conserved in cereals such as rice and maize, orthologs of FIS2 and MEA have not been reported (Spillane et al., 2007; Luo et al., 2009). Orthologs of the Arabidopsis FIE gene have been reported in both rice (OsFIE1 and OsFIE2) and maize (ZmFIE1 and ZmFIE2; Springer et al., 2002; Danilevskaya et al., 2003; Luo et al., 2009). OsFIE1 is expressed only in the endosperm, whereas OsFIE2 is expressed in all tissues tested (Luo et al., 2009; Nallamilli et al., 2013). OsFIE1 is an imprinted gene, and its expression is regulated by DNA and H3K9me2 methylation (Luo et al., 2009; Zhang et al., 2012). OsFIE2 has a critical role in normal endosperm development and grain filling (Nallamilli et al., 2013).Our understanding of the epigenetic regulation of rice seed development has improved significantly (Zemach et al., 2010; Luo et al., 2011; Rodrigues et al., 2013). However, how the epigenetic regulation during seed development is altered during environmental perturbations is not well characterized. Most research efforts in the past have focused on the grain-filling stage (when storage proteins and starch accumulate) under stressful conditions (Yamakawa et al., 2007). However, it is not known if and how an environmental stress that specifically occurs during early seed development impacts seed size in rice. Here, we present evidence that early rice seed development is highly sensitive to heat stress and results in seed size reduction. We suggest a molecular mechanism that involves the rice PRC2 gene OsFIE1 as a potential component involved in regulating seed enlargement under heat stress.     

APETALA1突变影响WRKY基因的基础表达

拟南芥APETALA1（AP1）既是一个花分生组织特征基因又是一个花器官特征基因,在花器官发育中控制花萼和花瓣的发育。通过GUS染色进一步证实AP1主要在茎尖、花萼、花瓣和花托的位置表达。启动子分析发现,AP1启动子区包含了包括W-box在内的大量顺式作用元件,暗示相关转录调控因子参与了对AP1的调控。21个WRKY基因单突变后并不改变AP1在花中的表达,但是AP1突变则增强了检测的10个WRKY基因中7个WRKY基因的表达,暗示AP1参与了对WRKY基因的基础表达的调控。这个结果也暗示AP1可能通过控制花萼和花瓣的发育从而参与了对花的基础抗性。