拟南芥ABA不敏感型突变体及其ABA结合特性

拟南芥的脱落醚（ABA）不敏感型突变体abi2,在对ABA的敏感性、气孔开度及种子休眠方面,与野生型有明显差异。通过3H－ABA与野生型对的亚细胞组分的结合分析,表明38000×g组分特异结合活性最高,结合最适温度为20℃,最适保温时间：20℃时为70min;0℃时为90min。由饱和曲线的Scatchard分析表明：abi2存在一种ABA结合位点,野生型有两种ABA结合位点。对3H－ABA结合的38000×g组分的SDS－PAGE电泳分析表明：野生型有3个结合活性峰,而abi2只有1个结合活性峰。     

ABA调控种子发育的研究进展

种子发育是一个复杂的生物学过程，受各种遗传和外界因素的调节，显著影响农作物特别是禾谷类作物的种子活力和产量与质量。脱落酸(ABA)是调控种子发育和萌发最重要的植物激素之一，其活性水平、信号转导及其LAFL网络在种子发育包括胚胎发生和成熟过程的调控中起关键作用。该文主要综述了近年来ABA调控种子发育的研究取得的重要进展，包括ABA代谢和信号转导对种子发育的调控，ABA与种子成熟转录因子(AFL-B3、FUS3、ABI3、LEC2等)的作用，以及ABA在种子发育中的作用机制，并提出了需要进一步研究的科学问题，为深入理解种子发育的分子机制提供参考，从而提高种子的活力、产量和质量。     

Farnesol kinase is involved in farnesol metabolism, ABA signaling and flower development in Arabidopsis

Farnesol, which is toxic to plant cells at high concentrations, is sequentially phosphorylated to farnesyl phosphate and farnesyl diphosphate. However, the genes responsible for the sequential phosphorylation of farnesol have not been identified and the physiological role of farnesol phosphorylation has not been fully elucidated. To address these questions, we confirmed the presence of farnesol kinase activity in Arabidopsis (Arabidopsis thaliana) membranes and identified the corresponding gene (At5g58560, FOLK). Heterologous expression in recombinant yeast cells established farnesol as the preferred substrate of the FOLK-encoded kinase. Moreover, loss-of-function mutations in the FOLK gene abolished farnesol kinase activity, caused an abscisic acid-hypersensitive phenotype and promoted the development of supernumerary carpels under water-stress conditions. In wild-type plants, exogenous abscisic acid repressed FOLK gene expression. These observations demonstrate a role for farnesol kinase in negative regulation of abscisic acid signaling, and provide molecular evidence for a link between farnesol metabolism, abiotic stress signaling and flower development.     

Separating parental environment from seed size effects on next generation growth and development in Arabidopsis

Plant growth and development is profoundly influenced by environmental conditions that laboratory experimentation typically attempts to control. However, growth conditions are not uniform between or even within laboratories and the extent to which these differences influence plant growth and development is unknown. Experiments with wild-type Arabidopsis thaliana were designed to quantify the influences of parental environment and seed size on growth and development in the next generation. A single lot of seed was planted in six environmental chambers and grown to maturity. The seed produced was mechanically sieved into small and large size classes then grown in a common environment and subjected to a set of assays spanning the life cycle. Analysis of variance demonstrated that seed size effects were particularly significant early in development, affecting primary root growth and gravitropism, but also flowering time. Parental environment affected progeny germination time, flowering and weight of seed the progeny produced. In some cases, the parental environment affected the magnitude of (interacted with) the observed seed size effects. These data indicate that life history circumstances of the parental generation can affect growth and development throughout the life cycle of the next generation to an extent that should be considered when performing genetic studies.     

Effect of abscisic acid on stomatal opening in isolated epidermal strips of abi mutants of Arabidopsis thaliana

Abscisic acid-insensitive mutants of Arabidopsis thaliana L. var. Landsberg erecta were selected for their decreased sensitivity to ABA during germination. Two of these mutants, abi-1 and abi-2 , display a wilty phenotype as adult plants, indicating disturbed water relations. Experiments were undertaken to find out if this results from insensitivity of mutant stomates to ABA.
Growth conditions and methods to isolate epidermal strips were optimized to study stomatal movement. Wild type stomates required external ionic conditions comparable to those found for other species such as Commelina communis . The largest light-induced opening of A. thaliana stomates was found at an external KCl concentration of 50 m M . Stomatal apertures were increased by lowering external Ca²⁺ to 0.05 m M . The apertures of stomates incubated with 10 μ M ABA were not altered by changes in Ca²⁺ from 0.05 to 1.0 m M .
Stomates of all abi mutants showed a light-stimulated stomatal opening. The opening of wild type and abi-3 stomates was inhibited by ABA, while stomates of abi-1 and abi-2 did not respond to ABA. The insensitivity of abi-1 and abi-2 stomates to ABA may thus explain the observed disturbed water relations.     

Disruptions in valine degradation affect seed development and germination in Arabidopsis

We have functionally characterized the role of two putative mitochondrial enzymes in valine degradation using insertional mutants. Prior to this study, the relationship between branched‐chain amino acid degradation (named for leucine, valine and isoleucine) and seed development was limited to leucine catabolism. Using a reverse genetics approach, we show that disruptions in the mitochondrial valine degradation pathway affect seed development and germination in Arabidopsis thaliana. A null mutant of 3‐hydroxyisobutyryl‐CoA hydrolase (CHY4, At4g31810) resulted in an embryo lethal phenotype, while a null mutant of methylmalonate semialdehyde dehydrogenase (MMSD, At2g14170) resulted in seeds with wrinkled coats, decreased storage reserves, elevated valine and leucine, and reduced germination rates. These data highlight the unique contributions CHY4 and MMSD make to the overall growth and viability of plants. It also increases our knowledge of the role branched‐chain amino acid catabolism plays in seed development and amino acid homeostasis.     

MiR397b regulates both lignin content and seed number in Arabidopsis via modulating a laccase involved in lignin biosynthesis

Plant laccase (LAC) enzymes belong to the blue copper oxidase family and polymerize monolignols into lignin. Recent studies have established the involvement of microRNAs in this process; however, physiological functions and regulation of plant laccases remain poorly understood. Here, we show that a laccase gene, LAC4, regulated by a microRNA, miR397b, controls both lignin biosynthesis and seed yield in Arabidopsis. In transgenic plants, overexpression of miR397b (OXmiR397b) reduced lignin deposition. The secondary wall thickness of vessels and the fibres was reduced in the OXmiR397b line, and both syringyl and guaiacyl subunits are decreased, leading to weakening of vascular tissues. In contrast, overexpression of miR397b‐resistant laccase mRNA results in an opposite phenotype. Plants overexpressing miR397b develop more than two inflorescence shoots and have an increased silique number and silique length, resulting in higher seed numbers. In addition, enlarged seeds and more seeds are formed in these miR397b overexpression plants. The study suggests that miR397‐mediated development via regulating laccase genes might be a common mechanism in flowering plants and that the modulation of laccase by miR397 may be potential for engineering plant biomass production with less lignin.     

A comparative study of seed yield parameters in Arabidopsis thaliana mutants and transgenics

Because seed yield is the major factor determining the commercial success of grain crop cultivars, there is a large interest to obtain more understanding of the genetic factors underlying this trait. Despite many studies, mainly in the model plant Arabidopsis thaliana, have reported transgenes and mutants with effects on seed number and/or seed size, knowledge about seed yield parameters remains fragmented. This study investigated the effect of 46 genes, either in gain- and/or loss-of-function situations, with a total of 64 Arabidopsis lines being examined for seed phenotypes such as seed size, seed number per silique, number of inflorescences, number of branches on the main inflorescence and number of siliques. Sixteen of the 46 genes, examined in 14 Arabidopsis lines, were reported earlier to directly affect in seed size and/or seed number or to indirectly affect seed yield by their involvement in biomass production. Other genes involved in vegetative growth, flower or inflorescence development or cell division were hypothesized to potentially affect the final seed size and seed number. Analysis of this comprehensive data set shows that of the 14 lines previously described to be affected in seed size or seed number, only nine showed a comparable effect. Overall, this study provides the community with a useful resource for identifying genes with effects on seed yield and candidate genes underlying seed QTL. In addition, this study highlights the need for more thorough analysis of genes affecting seed yield.     

The phs1-3 mutation in a putative dual-specificity protein tyrosine phosphatase gene provokes hypersensitive responses to abscisic acid in Arabidopsis thaliana

The plant hormone abscisic acid (ABA) controls numerous physiological traits: dormancy and germination of seeds, senescence and resistance to abiotic stresses. In order to get more insight into the role of protein tyrosine phosphatase (PTP) in ABA signalling, we obtained eight homozygous T-DNA insertion lines in Arabidopsis thaliana PTP genes. One mutant, named phs1-3, exhibited a strong ABA-induced inhibition of germination as only 26% of its seeds germinated after 3 days instead of 92% for the Columbia (Col-0) line. Genetic and molecular analyses of phs1-3 showed that it bears a unique T-DNA insertion in the promoter of the gene and that the mutation is recessive. PHS1 expression in the mutant is about half that of the Col-0 line. The upregulation of two ABA-induced genes (At5g06760, RAB18) and the downregulation of two ABA-repressed genes (AtCLC-A, ACL) are enhanced in the phs1-3 mutant compared with the wild-type. The 'in planta' aperture of phs1-3 stomata is reduced and the inhibition of the light-induced opening of stomata by ABA is stronger in phs1-3 leaves than in Col-0 leaves. Finally, PHS1 expression is upregulated in the presence of ABA in both phs1-3 and Col-0 but more intensively in the mutant. Thus, phs1-3 is hypersensitive to ABA. Taken together, these results show that PHS1, which encodes a dual-specificity PTP, is a negative regulator of ABA signalling.     

Control of seed development in Arabidopsis thaliana by atmospheric oxygen

Seed development is known to be inhibited completely when plants are grown in oxygen concentrations below 5·1 kPa, but apart from reports of decreased seed weight little is known about embryogenesis at subambient oxygen concentrations above this critical level. Arabidopsis thaliana (L.) Heynh. plants were grown full term under continuous light in premixed atmospheres with oxygen partial pressures of 2·5, 5·1, 10·1, 16·2 and 21·3 kPa O₂, 0·035 kPa CO₂ and the balance nitrogen. Seeds were harvested for germination tests and microscopy when siliques had yellowed. Seed germination was depressed in O₂ treatments below 16·2 kPa, and seeds from plants grown in 2·5 kPa O₂ did not germinate at all. Fewer than 25% of the seeds from plants grown in 5·1 kPa oxygen germinated and most of the seedlings appeared abnormal. Light and scanning electron microscopic observation of non-germinated seeds showed that these embryos had stopped growing at different developmental stages depending upon the prevailing oxygen level. Embryos stopped growing at the heart-shaped to linear cotyledon stage in 5·1 kPa O₂, at around the curled cotyledon stage in 10·1 kPa O₂, and at the premature stage in 16·2 kPa O₂. Globular and heart-shaped embryos were observed in sectioned seeds from plants grown in 2·5 kPa O₂. Tissue degeneration caused by cell autolysis and changes in cell structure were observed in cotyledons and radicles. Transmission electron microscopy of mature seeds showed that storage substances, such as protein bodies, were reduced in subambient oxygen treatments. The results demonstrate control of embryo development by oxygen in Arabidopsis .