CRM1/BIG-mediated auxin action regulates Arabidopsis inflorescence development

The shape of the inflorescence in Arabidopsis thaliana ecotype Columbia is a raceme with individual flowers developing acropetally. The ecotype Landsberg harboring the erecta (er) mutation shows a corymb-like inflorescence, namely a compact inflorescence with a flattened arrangement of flower buds at the tip. To gain insight into inflorescence development, we previously isolated corymb-like inflorescence mutants, named corymbosa1 (crm1), and found that the corymb-like inflorescence in crm1-1 was due to reduced cell elongation of pedicels and stem internodes. Double mutants of crm1 with er and crm2, and crm1-1 crm2-1 er-105 triple mutants show an additive phenotype. crm1-1 is caused by a mutation in BIG, which is required for polar auxin transport. CRM1/BIG is expressed in inflorescence meristems, floral meristems and vascular tissues. We analyzed a collection of 12 reduced lateral root formation (rlr) mutants, which are allelic to crm1-1, and categorized the mutants into three classes, depending on the plant developmental defects. Although all 12 alleles had new stop codons, the phenotype of heterozygous crm1-1/doc1-1 and Northern blotting suggest that new crm1/big mutant alleles are hypomorphic. Auxin-responsive DR5rev::GFP expression was decreased in crm1-1 vasculature of pedicels and stem internodes. PINFORMED1 (PIN1) and CRM1/BIG are expressed in vasculature of pedicels and stem internodes. The severity of corymb-like inflorescence in crm1/big mutants correlated with increased levels of PIN1. Our results suggest that CRM1/BIG controls the elongation of the pedicels and stem internodes through auxin action.     

外源BoCAL基因对花椰菜花球形态发生的调节及其遗传

花椰菜和结球甘蓝是芸薹属甘蓝种的两个变种,前者的BoCAL基因发生提前终止突变而失去了原有的功能,而后者的BoCAL基因具有完整的编码区。在农杆菌的介导下,我们获得了BoCAL转基因花椰菜。T2代的遗传研究表明,外源BoCAL基因转入后花椰菜转基因植株都没有形成花球,而是只形成松散的由花蕾组成的绿色花序。这一结果说明,花椰菜BobCAL被甘蓝BoCAL互补了,转基因花椰菜因此失去了形成花球的能力。这些转基因植株自交到T3代时花序的形态特征与T2代一致,为松散的绿色花序,但是花序出现的时间与T1代相比提早了15天。将转基因花椰菜与野生型花椰菜杂交,结果发现杂交后代的植株形成夹杂有花蕾的花球,且花序出现的时间大大推迟,在播种后135天后才形成花球。     

外源BoCAL基因对花椰菜花球形态发生的调节及其遗传

花椰菜和结球甘蓝是芸薹属甘蓝种的两个变种,前者的BobCAL基因发生提前终止突变而失去了原有的功能,而后者的BoCAL基因具有完整的编码区。在农杆菌的介导下,我们获得了BoCAL转基因花椰菜。T_2代的遗传研究表明,外源BoCAL基因转入后花椰菜转基因植株都没有形成花球,而是只形成松散的由花蕾组成的绿色花序。这一结果说明,花椰菜BobCAL被甘蓝BoCAL互补了,转基因花椰菜因此失去了形成花球的能力。这些转基因植株自交到T_3代时花序的形态特征与T_2代一致,为松散的绿色花序,但是花序出现的时间与T_1代相比提早了15天。将转基因花椰菜与野生型花椰菜杂交,结果发现杂交后代的植株形成夹杂有花蕾的花球,且花序出现的时间大大推迟,在播种后135天后才形成花球。     

Requirement of the Auxin Polar Transport System in Early Stages of Arabidopsis Floral Bud Formation

The pin-formed mutant pin 1-1, one of the Arabidopsis flower mutants, has several structural abnormalities in inflorescence axes, flowers, and leaves. In some cases, pin1-1 forms a flower with abnormal structure (wide petals, no stamens, pistil-like structure with no ovules in the ovary) at the top of inflorescence axes. In other cases, no floral buds are formed on the axes. An independently isolated allelic mutant (pin1-2) shows similar phenotypes. These mutant phenotypes are exactly the same in wild-type plants cultured in the presence of chemical compounds known as auxin polar transport inhibitors: 9-hydroxyfluorene-9-carboxylic acid or N-(1-naphthyl)phthalamic acid. We tested the polar transport activity of indole-3-acetic acid and the endogenous amount of free indole-3-acetic acid in the tissue of inflorescence axes of the pin1 mutants and wild type. The polar transport activity in the pin 1-1 mutant and in the pin1-2 mutant was decreased to 14% and 7% of wild type, respectively. These observations strongly suggest that the normal level of polar transport activity in the inflorescence axes is required in early developmental stages of floral bud formation in Arabidopsis and that the primary function of the pin1 gene is auxin polar transport in the inflorescence axis.     

A Mutation in the Arabidopsis TFL1 Gene Affects Inflorescence Meristem Development

We present the initial phenotypic characterization of an Arabidopsis mutation, terminal flower 1-1 (tfl1-1), that identifies a new genetic locus, TFL1. The tfl1-1 mutation causes early flowering and limits the development of the normally indeterminate inflorescence by promoting the formation of a terminal floral meristem. Inflorescence development in mutant plants often terminates with a compound floral structure consisting of the terminal flower and one or two subtending lateral flowers. The distal-most flowers frequently contain chimeric floral organs. Light microscopic examination shows no structural aberrations in the vegetative meristem or in the inflorescence meristem before the formation of floral buttresses. The wild-type appearance of lateral flowers and observations of double mutant combinations of tfl1-1 with the floral morphogenesis mutations apetala 1-1 (ap1-1), ap2-1, and agamous (ag) suggest that the tfl1-1 mutation does not affect normal floral meristems. Secondary flower formation usually associated with the ap1-1 mutation is suppressed in the terminal flower, but not in the lateral flowers, of tfl1-1 ap1-1 double mutants. Our results suggest that tfl1-1 perturbs the establishment and maintenance of the inflorescence meristem. The mutation lies on the top arm of chromosome 5 approximately 2.8 centimorgans from the restriction fragment length polymorphism marker 217.     

The Arabidopsis ERECTA gene encodes a putative receptor protein kinase with extracellular leucine-rich repeats.

Arabidopsis Landsberg erecta is one of the most popular ecotypes and is used widely for both molecular and genetic studies. It harbors the erecta (er) mutation, which confers a compact inflorescence, blunt fruits, and short petioles. We have identified five er mutant alleles from ecotypes Columbia and Wassilewskija. Phenotypic characterization of the mutant alleles suggests a role for the ER gene in regulating the shape of organs originating from the shoot apical meristem. We cloned the ER gene, and here, we report that it encodes a putative receptor protein kinases. The deduced ER protein contains a cytoplasmic protein kinase catalytic domain, a transmembrane region, and an extracellular domain consisting of leucine-rich repeats, which are thought to interact with other macromolecules. Our results suggest that cell-cell communication mediated by a receptor kinase has an important role in plant morphogenesis.     

龙眼花芽形成及其调控研究进展(综述)

龙眼正常的花芽分化和“冲销”的分化过程差异很大。其花芽分化与营养、温度、光照、水分、内源激素的关系密切。应用各种措施进行龙眼花芽形成及产期调控取得了良好的效果,但仍存在诸多问题需要进一步深入研究。     

穗花牡荆花芽分化过程中形态和生理指标变化

以穗花牡荆为研究材料,通过探究其花芽分化进程和生理特性,为花期调控技术提供成花机理。采用物候期观察和石蜡切片相结合的方法并测定花芽分化过程中相关生理指标,研究花发育过程中的形态和生理变化。结果表明,穗花牡荆花芽分化为一年多次分化型,其进程可划分为七个时期：未分化期、总轴花序原基分化期、初级分轴花序原基分化期、次级分轴花序原基分化期、小花原基分化期、花器官分化前期和花器官分化后期。同一植株不同位置花芽及同一花序中不同单花分化的进程不同,第一季花期后各阶段的花芽分化形态常存在重叠。花芽分化过程中不同时期叶片和花芽的可溶性糖和可溶性蛋白质含量均有上升下降的变化,总体上叶片中营养物质含量高于花芽保证营养供应。花芽分化过程中,IAA、ABA、CTK和GA3整体水平上先升后降有利于花芽分化进行。研究认为,花芽中大量的可溶性糖和蛋白质积累及较高的碳氮比,有利于穗花牡荆花芽形态分化顺利完成。低水平的GA3/ABA和IAA/CTK有利于花序的形成,ABA/CTK和ABA/IAA比值升高促进小花原基和小花萼片原基的分化, GA3/CTK、GA3/ABA和GA3/IAA比值升高促进花瓣原基、雄雌蕊原基发育。     

Determination for inflorescence development is a stable state,separable from determination for flower development in Pisum sativum L. buds

Terminal meristems of Pisum sativum (garden pea) transit from vegetative to inflorescence development, and begin producing floral axillary meristems. Determination for inflorescence development was assessed by culturing excised buds and meristems. The first node of floral initiation (NFI) for bud expiants developing in culture and for adventitious shoots forming on cultured meristems was compared with the NFI of intact control buds. When terminal buds having eight leaf primordia were excised from plants of different ages (i.e., number of unfolded leaves) and cultured on 6-benzylaminopurine and kinetin-supplemented medium, the NFI was a function of the age of the source plant. By age 3, all terminal buds were determined for inflorescence development. Determination occurred at least eight nodes before the first axillary flower was initiated. Thus, the axillary meristems contributing to the inflorescence had not formed at the time the bud was explanted. Similar results were obtained for cultured axillary buds. In addition, meristems excised without leaf primordia from axillary buds three nodes above the cotyledons of age-3 plants gave rise to adventitious buds with an NFI of 8.3 ±0.3 nodes. In contrast seed-derived plants had an NFI of 16.5 ±0.2. Thus cells within the meristem were determined for inflorescence development. These findings indicate that determination for inflorescence development in P. sativum is a stable developmental state, separable from determination for flower development, and occurring prior to initiation of the inflorescence at the level of meristems.     

Pedicel development in Arabidopsis thaliana: contribution of vascular positioning and the role of the BREVIPEDICELLUS and ERECTA genes

Although the regulation of Arabidopsis floral meristem patterning and determinacy has been studied in detail, very little is known about the genetic mechanisms directing development of the pedicel, the short stem linking the flower to the inflorescence axis. Here, we provide evidence that the pedicel consists of a proximal portion derived from the young flower primordium, and a bulged distal region that emerges from tissue at the bases of sepals in the floral bud. Distal pedicel growth is controlled by the KNOTTED1-like homeobox gene BREVIPEDICELLUS (BP), as 35S::BP plants show excessive proliferation of pedicel tissue, while loss of BP conditions a radial constriction around the distal pedicel circumference. Mutant radial constrictions project proximally along abaxial and lateral sides of pedicels, leading to occasional downward bending at the distal pedicel. This effect is severely enhanced in a loss-of-function erecta (er) background, resulting in radially constricted tissue along the entire abaxial side of pedicels and downward-oriented flowers and fruit. Analysis of pedicel vascular patterns revealed biasing of vasculature towards the abaxial side, consistent with a role for BP and ER in regulating a vascular-borne growth inhibitory signal. BP expression in a reporter line marked boundaries between the inflorescence stem and lateral organs and the receptacle and floral organs. This boundary expression appears to be important to prevent homeotic displacement of node and lateral organ fates into underlying stem tissue. To investigate interactions between pedicel and flower development, we crossed bp er into various floral mutant backgrounds. Formation of laterally-oriented bends in bp lfy er pedicels paralleled phyllotaxy changes, consistent with a model where the architecture of mutant stems is controlled by both organ positioning and vasculature patterns. Collectively, our results indicate that the BP gene acts in Arabidopsis stems to confer a growth-competent state that counteracts lateral-organ associated asymmetries and effectively radializes internode and pedicel growth and differentiation patterns.     

Gene TAENIATA is a novel negative regulator of the Arabidopsis thaliana homeobox genes KNAT1, KNAT2, KNAT6, and STM

Mutant Arabidopsis thaliana taeniata (tae) plants are characterized by an altered morphology of leaves and the inflorescence. At the beginning of flowering, the inflorescence produces fertile flowers morphologically intermediate between a shoot and a flower. The recessive mutation tae also causes the formation of ectopic meristems and shoot rosettes on leaves. The expressivity of the mutant characters depend on the temperature and photoperiod. Analysis of the activity of KNOX class I genes in the leaves of the tae mutant has demonstrated the expression of genes KNAT2 and STM and an increase in the expression of genes KNAT1 and KNAT6 compared to wild-type leaves. These data indicate that the TAE gene negatively regulates the KNAT1, KNAT2, KNAT6, and STM genes.     

Role of hormones on flower bud formation in thin-layer expiants of tobacco

Flower bud formation was studied in thin-layer tissue expiants of epidermis plus subepidermal cortex from the inflorescence ramifications ofNicotiana tabacum cv. Samsun. With appropriate hormone concentrations of BA and NAA expiants from flowerv and fruitbearing stalks regenerate flower buds only, while those from the internodes of the inflorescence ramifications produce generative as well as vegetative buds. In both types of expiants the number of buds formed depend mainly on the hormone concentrations but, in addition, the age of stalks and internodes from which expiants are taken also affects bud formation. Both ABA and JA inhibit flower bud formation in expiants of flower stalks. JA was shown to particularly inhibit bud initiation.     

Study of the effect of the gene ERECTA2 on the development of Arabidopsis thaliana shoot

The role of the gene ER2 in plant development has been studied by the analysis of the erecta2 (er2) mutant of Arabidopsis thaliana (L.) Heynh. It was shown that the mutation er2 provides pleiotropic effect on the development of all aboveground organs. It induces shortening and thickening of the stem, leaves and all flower organs, though it does not change the sensitivity to gibberellin. Changes in the morphology of the shoot organs are due to the changes in cell polarity. The cells get wider and shorter compared to the wild type. It was found that the gene ER2 is located in the lower arm of the chromosome 1. It complementarily interacts with the gene ER that plays an important role in the control of intercellular interactions.     

板栗花芽分化和花序生长过程中的内源激素含量变化

在板栗花芽分化期间,易于形成雌花的上部芽含有较高的ZT、GA和较低的ABA;下部芽则基本相反。在前2个分化期,上部芽的IAA含量均比下部芽的低,但进入第三分化期,尤其是随着萌芽期的到来,上部芽的IAA含量迅速急剧上升,远远超过下部芽。在花序生长期,1、2花序基部保持较高的ZT和GA水平,1、2花序顶部和5、6花序则保持较高的IAA和ABA水平。