The Critical Requirement for Linolenic Acid Is Pollen Development,Not Photosynthesis,in an Arabidopsis Mutant

The very high proportions of trienoic fatty acids found in chloroplast membranes of all higher plants suggest that these lipid structures might be essential for photosynthesis. We report here on the production of Arabidopsis triple mutants that contain negligible levels of trienoic fatty acids. Photosynthesis at 22[deg]C was barely affected, and vegetative growth of the mutants was identical with that of the wild type, demonstrating that any requirement for trienoic acyl groups in membrane structure and function is relatively subtle. Although vegetative growth and development were unaffected, the triple mutants are male sterlle and produce no seed under normal conditions. Comparisons of pollen development in wild-type and triple mutant flowers established that pollen grains in the mutant developed to the tricellular stage. Exogenous applications of [alpha]-llnolenate or jasmonate restored fertility. Taken together, the results demonstrate that the critical role of trienoic acids in the life cycle of plants is as the precursor of oxylipin, a signaling compound that regulates final maturation processes and the release of pollen.     

Genetic Interactions That Regulate Inflorescence Development in Arabidopsis

In Arabidopsis, floral meristems arise in continuous succession directly on the flanks of the inflorescence meristem. Thus, the pathways that regulate inflorescence and floral meristem identity must operate both simultaneously and in close spatial proximity. The TERMINAL FLOWER 1 (TFL1) gene of Arabidopsis is required for normal inflorescence meristem function, and the LEAFY (LFY), APETALA 1 (AP1), and APETALA 2 (AP2) genes are required for normal floral meristem function. We present evidence that inflorescence meristem identity is promoted by TFL1 and that floral meristem identity is promoted by parallel developmental pathways, one defined by LFY and the other defined by AP1/AP2. Our analysis suggests that the acquisition of meristem identity during inflorescence development is mediated by antagonistic interactions between TFL1 and LFY and between TFL1 and AP1/AP2. Based on this study, we propose a simple model for the genetic regulation of inflorescence development in Arabidopsis. This model is discussed in relation to the proposed interactions between the inflorescence and the floral meristem identity genes and in regard to other genes that are likely to be part of the genetic hierarchy regulating the establishment and maintenance of inflorescence and floral meristems.     

An Inhibitor of Tryptophan-Dependent Biosynthesis of Indole-3-Acetic Acid Alters Seedling Development in Arabidopsis

Although polar transport and the TIR1-dependent signaling pathway of the plant hormone auxin/indole-3-acetic acid (IAA) are well characterized, understanding of the biosynthetic pathway(s) leading to the production of IAA is still limited. Genetic dissection of IAA biosynthetic pathways has been complicated by the metabolic redundancy caused by the apparent existence of several parallel biosynthetic routes leading to IAA production. Valuable complementary tools for genetic as well as biochemical analysis of auxin biosynthesis would be molecular inhibitors capable of acting in vivo on specific or general components of the pathway(s), which unfortunately have been lacking. Several indole derivatives have been previously identified to inhibit tryptophan-dependent IAA biosynthesis in an in vitro system from maize endosperm. We examined the effect of one of them, 6-fluoroindole, on seedling development of Arabidopsis thaliana and tested its ability to inhibit IAA biosynthesis in feeding experiments in vivo. We demonstrated a correlation of severe developmental defects or growth retardation caused by 6-fluoroindole with significant downregulation of de novo synthesized IAA levels, derived from the stable isotope-labeled tryptophan pool, upon treatment. Hence, 6-fluoroindole shows important features of an inhibitor of tryptophan-dependent IAA biosynthesis both in vitro and in vivo and thus may find use as a promising molecular tool for the identification of novel components of the auxin biosynthetic pathway(s).     

EMF Genes Interact with Late-Flowering Genes to Regulate Arabidopsis Shoot Development

To investigate the genetic mechanisms regulating the transitionfrom vegetative to reproductive phase in Arabidopsis, doublemutants between two embryonic flower (emf) and 12 differentlate-flowering mutants were constructed and analyzed. Doublemutants in all combinations displayed the emf phenotypes withoutforming rosettes during early development; however, clear variationsbetween different double mutants were observed during late development,fwa significantly enhanced the vegetative property of both emfmutants by producing a high number of sessile leaves withoutany further reproductive growth in emf1 fwa double mutants.It also produced numerous leaf-like flower structures similarto those in leafy ap1 double mutant in emf1 fwa double mutants.Nine late-flowering mutants, ft, fca, ld, fd, fpa, fe, fy, fha,and fve, caused different degrees of increase in the numberof sessile leaves, the size of inflorescence, and the numberof flowers only in weak emf1 and emf2 mutant alleles background.Two late-flowering mutants, co and gi, however, had no effecton either emf1 and emf2 mutant alleles in double mutants. Ourresults suggest that FWA function in distinct pathways fromboth EMF genes to regulate flower competence by activating geneswhich specify floral meristem identity. CO and GI negativelyregulate both EMF genes, whereas the other nine late-floweringgenes may interact with EMF genes directly or indirectly toregulate shoot maturation in Arabidopsis. ¹ To whom correspondence should be addressed.     

LEAFY Interacts with Floral Homeotic Genes to Regulate Arabidopsis Floral Development

In the leafy mutant of Arabidopsis, most of the lateral meristems that are fated to develop as flowers in a wild-type plant develop as inflorescence branches, whereas a few develop as abnormal flowers consisting of whorls of sepals and carpels. We have isolated several new alleles of leafy and constructed a series of double mutants with leafy and other homeotic mutants affecting floral development to determine how these genes interact to specify the developmental fate of lateral meristems. We found that leafy is completely epistatic to pistillata and interacts additively with agamous in early floral whorls, whereas in later whorls leafy is epistatic to agamous. Double mutants with leafy and either apetala1 or apetala2 showed a complete loss of the whorled phyllotaxy, shortened internodes, and suppression of axillary buds typical of flowers. Our results suggest that the products of LEAFY, APETALA1, and APETALA2 together control the differentiation of lateral meristems as flowers rather than as inflorescence branches.     

Metabolism of Unsaturated Monogalactosyldiacylglycerol Molecular Species in Arabidopsis thaliana Reveals Different Sites and Substrates for Linolenic Acid Synthesis

Synthesis of unsaturated monogalactosyldiacylglycerol (MGDG) was examined in a mutant of Arabidopsis thaliana (L.) Heynh. containing reduced levels of hexadecatrienoic (16:3) and linolenic (18:3) acids in leaf lipids. Molecular species composition and labeling kinetics following the incorporation of exogenous [¹⁴C]fatty acids suggest that at least two pathways and multiple substrates are involved in desaturation of linoleic acid (18:2) to 18:3 for production of unsaturated galactolipids. A reduction in 18:3/16:3 MGDG and an increase in 18:2/16:2 MGDG, together with labeling kinetics of these molecular species following the incorporation of exogenous [¹⁴C]12:0 fatty acids, suggests that a chloroplastic pathway for production of 18:3 at the sn-1 position of MGDG utilizes 18:2/16:2 MGDG as a substrate. This chloroplastic (prokaryotic) pathway is deficient in the mutant. When exogenous [¹⁴C]18:1 was supplied, a eukaryotic (cytoplasmic) pathway involving the desaturation of 18:2 to 18:3 on phosphatidylcholine serves as the source of 18:3 for the sn-2 position of MGDG. This eucaryotic pathway predominates in the mutant.     

Mutagenic Activity of Autoxidized Linolenic and Linoleic Acid

Isolation of mutants with an enhanced productivity of 7β-(4-carboxybutanamido)-cephalosporanic acid acylase (penicillin amidohydrolase, EC 3.5.1.11) was attempted. A mutant, Ci-36, isolated by a method using glutarylamlide, produced approximately 5-times more acylase than did the parental strain. However, this acylase formation was still dependent on glutaric acid which was previously found to be essential in the case of the wild strain, Pseudomonas SY-77-1. The inducible-acylase formation was found to be firmly associated with the process of cell multiplication. Subsequently, a mutant, GK-16 was derived from Ci-36, which was shown to produce the acylase at maximum level without the addition of glutaric acid. The productivity of GK-16 was 2.4-times higher than that of Ci-36.     

Desmutagenic Activity of Peroxidase on Autoxidized Linolenic Acid

L-Arginine analog-resistant mutants were derived from Bacillus subtilis, Serratia marcescens, Microbacterium ammoniaphilum, Micrococcus sodonensis, Nocardia corynebacteroides, N. rubra, Saccharomyces cerevisiae and Candida tropicalis.The mutants of all species tested produced an appreciable amount of L-arginine. The arginine productivity of SAH4-7, an L-arginine hydroxamate-resistant L-arginine-producer of B. subtilis,increased stepwisely by successively introducing such characters as pyrimidine analog-, histidine analog-, and tryptophan analog-resistance and then increased resistance to arginine analog. The mutant strain finally selected was KY7690 and it produced ca. 17mg per ml of L-arginine.     

Dihydroactinidiolide,a High Light-Induced 13-Carotene Derivative that Can Regulate Gene Expression and Photoacclimation in Arabidopsis

Dear Editor,
The physiological functions of carotenoids in plants go beyond their traditional roles as accessory light-har- vesting pigments, natural colorants, and quenchers of tri- plet chlorophyll and singlet oxygen （102）. Recent studies have indeed emphasized the functional role of molecules derived from carotenoids as phytohormones （Ruyter-Spira et al., 20β） or messengers in stress signaling pathways （Havaux, 2014）. In particular, chemical quenching of 102 by carotenoids within the photosystems involves oxidation of the carotenoid molecules, generating a variety of oxi- dized products （Ramel et al., 2012）. β-Cyclocitral, a volatile C7 derivative of β-carotene, is one such molecule produced during high light stress, which was found to induce changes in the expression of 102-responsive genes （Ramel et al., 2012）. Moreover, the β-cyclocitral-dependent gene repro- gramming was associated with an increased tolerance of the plants to photooxidative stress. These effects appeared to be specific to β-cyclocitral since they were not observed with β-ionone, a C9-oxidized derivative of ~-carotene, which was not able to induce or repress the expression of 1O2 gene markers. Based on those results, it was pro- posed that β-cyclocitral is a plastid messenger involved in the chloroplast-to-nucleus 1O2 signaling pathway lead- ing to acclimation to high light stress （Ramel et al., 2012）. However, in vitro 102 oxidation of β-carotene is known to produce other volatile compounds besides β-cyclocitral and IB-ionone, such as dihydroactinidiolide （dhA, Figure 1A） and a-ionene （Ramel et al., 2012）. The dhA molecule is a lac- tone （cyclic ester） resulting from the secondary oxidation of β-ionone through the intermediate 5,6-epoxy-β-ionone （Havaux, 2014）. Both dhA and o-ionene were detected in plant leaves and fruits （e.g. Del Mar Caja et al., 2009; Ramel et al., 2012）. Interestingly, dhA, but not o-ionene, was reported to accumulate in Arabidopsis leaves under hiclh liclht str     

Cryptochromes,Phytochromes, and COP1 Regulate Light-Controlled Stomatal Development in Arabidopsis

In Arabidopsis thaliana, the cryptochrome (CRY) blue light photoreceptors and the phytochrome (phy) red/far-red light photoreceptors mediate a variety of light responses. COP1, a RING motif–containing E3 ubiquitin ligase, acts as a key repressor of photomorphogenesis. Production of stomata, which mediate gas and water vapor exchange between plants and their environment, is regulated by light and involves phyB and COP1. Here, we show that, in the loss-of-function mutants of CRY and phyB, stomatal development is inhibited under blue and red light, respectively. In the loss-of-function mutant of phyA, stomata are barely developed under far-red light. Strikingly, in the loss-of-function mutant of either COP1 or YDA, a mitogen-activated protein kinase kinase kinase, mature stomata are developed constitutively and produced in clusters in both light and darkness. CRY, phyA, and phyB act additively to promote stomatal development. COP1 acts genetically downstream of CRY, phyA, and phyB and in parallel with the leucine-rich repeat receptor-like protein TOO MANY MOUTHS but upstream of YDA and the three basic helix-loop-helix proteins SPEECHLESS, MUTE, and FAMA, respectively. These findings suggest that light-controlled stomatal development is likely mediated through a crosstalk between the cryptochrome-phytochrome-COP1 signaling system and the mitogen-activated protein kinase signaling pathway.     

气相色谱质谱联用技术对栝楼籽油亚麻酸和亚油酸含量的分析

通过皂化法和尿素包合法对热榨、冷榨栝楼（Trichosanthes kirilowii）籽油进行提取,采用气相色谱-质谱联用（GC-MS）技术检测分析栝楼籽油中亚麻酸、亚油酸成分、含量。结果表明,热榨栝楼籽油中亚麻酸相对含量为4.16%～11.58%,亚油酸相对含量为68.62%～95.84%。冷榨栝楼籽油中不含亚麻酸成分。此方法适用于栝楼籽油的成分分析。     

Overexpression of AHL20 Negatively Regulates Defenses in Arabidopsis

Plants are equipped to recognize invading pathogenic microbes and activate innate immune responses by sensing pathogen-associated molecular patterns (PAMPs). PAMP-triggered immunity (PTI) is critical for plant resistance to potential pathogens. Although the mechanism by which PTI is activated has been intensively studied, exactly how plants prevent unregulated immune responses is less well understood. Here we provide evidence that AHL20, an AT-hook containing DNA-binding protein, negatively regulates PTI. Overexpression of AHL20 as a stable transgene suppressed PAMP-induced NHO1 and FRK1 expression in Arabidopsis plants. Similarly, transient expression of the closely related family members AHL19, AHL15, and AHL27 in protoplasts also blocked PAMP-induced gene expression. The AHL20 overexpression plants displayed greater susceptibility to virulent Pseudomonas syringae bacteria. These results indicate that AHL proteins play an important role in plant immunity.