植物体内生长素合成的研究进展

植物体内生长素合成的研究进展 生长素的种类、作用、合成途径,生长素早在1880年达尔文通过胚芽鞘实验就被发现,也是最早被发现的一种植物激素。1930年鉴定是吲哚乙酸(IAA)。,生长素的发现,生长素的作用,生长素作为植物体内最重要的激素 ,调控着植物生长和发育等重要过程 ,如影响细胞的伸长、分裂和分化 ,促进根茎叶的生长、维管组织分化、顶端优势和向地性以及向光反应等； 生长素对生长的促进作用主要是促进细胞的生长，特别是细胞的伸长，对细胞分裂没有影响。,生长素在体内的分布和运输,1.分布：不同植物、不同器官生长素的分布不同 植物体内常见的生长素类似物： IAA 、NAA 、吲哚乙腈、IBA 2.运输：Polar Auxin Transport(PAT)极性运输 形态学上端（apical side）形态学下端（basal side） 韧皮部运输 （运输需要载体和ATP） 3.IAA抑制物：缺氧、2,3，5-三碘苯甲酸 4.IAA运输的载体 influx carriers : Aux1，PGD4 efflix carriers : PINS， PGP1， PGP19,生长素的合成途径,(2) 吲哚-3-乙醛肟（IAOx） 途径：在拟南芥中已确定CYP79B2/CYP79B3基因编码的细胞色素P450酶，将色氨酸转化为吲哚-3-乙醛肟（IAOx），但拟南芥以外的十字花科中不存在。 IAOx被转换吲哚-3-乙腈（IAN）的途径是未知的，IAN由腈水解酶转换到IAA。编码腈水解酶的基因已经在玉米和拟南芥中被确定。然而，由于缺乏CYP79B2/ 3的同源基因和缺乏可检测到的IAOx水平。有人质疑在玉米这一途径的存在。,（3）色胺（TAM）途径：将Trp转化为TAM的酶是不知道的，但是在拟南芥中的YUCCA（YUC）编码的酶催化TAM转化为N羟色胺（HTAM）是被报道过的，YUC在发育的各个方面发挥着重要的作用，然而，YUC生化功能，特别是HTAM的作用最近受到质疑，需要进一步研究。 在玉米，稀疏基因（SPI1）是单子叶特定基因YUC家族的成员，表明TAM这个途径在玉米花序发展也很重要。该基因的另一位家庭成员（ZM-YUC1，这是更类似于AT-YUC10和AT-YUC11）是专门在胚乳表达，说明了这个基因家族的组织特异性调控。,（4）吲哚-3-丙酮酸（IPA）途径：在拟南芥中，通过色氨酸转氨酶（TAA1）和相关蛋白TAR1和TAR2，将Trp被转换为IPA，不知道IPA是如何转换为吲哚-3-乙醛（IAAId），但在玉米和拟南芥中已确定，醛氧化酶催化IAAId转化为生长素的。 这里我们将鉴定vt2，它是是玉米中TAA1/TAR1/TAR2的同源基因。,vanishing tassel2 Encodes a Grass-Specific Tryptophan Aminotransferase Required for Vegetative and Reproductive Development in Maize,The Plant Cell, Vol. 23: 550566, February 2011 Kimberly A. Phillips, Andrea L. Skirpan,Main content,Abstract Introduction Results Discussion Methods Summary,Abstract,we report the positional cloning and characterization of the vanishing tassel2 (vt2) gene of maize. Phylogenetic analyses indicate that vt2 is a co-ortholog of TAA1, which converts Trp to indole-3-pyruvic（丙酮） acid（IPA） in one of four hypothesized Trp-dependent auxin biosynthesis pathways.,vt2 mutants have dramatic effects on vegetative and reproductive development. vt2 mutants share many similarities with sparse inflorescence1 (spi1) mutants in maize. Both spi1 and vt2 function in auxin biosynthesis in maize, possibly in the same pathway rather than independently as previously proposed.,Introduction,Auxin has been shown to play a critical role in all stages of plant development. Auxin transport is crucial for providing the source of auxin required for organogenesis. In plants, there are hypothesized to be four Trp-dependent and one Trp-independent pathway for the biosynthesis of auxin in its most common form, indole-3-acetic acid (IAA).,Here, we identify vanishing tassel2 (vt2), a maize co-ortholog of TAA1/TAR1/TAR2.,Both the TAA1 and YUC gene families exhibit genetic redundancy and function in auxin biosynthesis, which raises the question of why neither pathway can compensate for the other.,1. vt2 Functions in Vegetative Development，Inflorescence Development， Axillary（腋窝） Meristem Formation during Inflorescence Development 2. vt2 Does Not Functionin Axillary Meristem Formation during Vegetative Development 3. Positional Cloning of vt2 4. vt2 Is Co-Orthologous to Trp Aminotransferases from Arabidopsis 5. vt2 Is Expressed in the Epidermis and Vasculature ,Results,1.vt2 Functions in Vegetative Development,As there is no difference in the timing of the juvenile-to-adult transition in vt2 mutants, this indicates that the later-formed adult leaves are those that are missing in vt2 mutants.,2. vt2 Functions in Inflorescence Development (1)vt2 mutants showed severe defects in the inflorescence,To test whether the reduction in tassel length in vt2 was caused by a reduction in cell size, the length of cells in the epidermis of the mature tassel was measured. vt2 mutants exhibited a 63% reduction in epidermal cell length compared with normal siblings. Therefore, the reduced tassel length in vt2 mutants is likely due to reduced cell elongation.,(2) vt2 mutants showed severe defects in the female inflorescence,3.vt2 Functions in Axillary Meristem Formation during Inflorescence Development,SPM：spikelet pair meristems BMs：branch meristems SMs ：two spikelet meristems,In vt2 mutant tassels grown under typical warm maize greenhouse growing conditions, we observed a very weak phenotype.,In wild-type greenhouse-grown plants, SPMs on the branches and main spike gave rise to two spikelet meristems (SMs).,vt2 mutant tassel F:greenhouse-grown GHI:cooler greenhouse,4. vt2Does Not FunctioninAxillary MeristemFormationduring Vegetative Development,5. Positional Cloning of vt2,6. vt2 Is Co-Orthologous to Trp Aminotransferases from Arabidopsis,7. vt2 Is Expressed in the Epidermis and Vasculature,spm，spikelet（副穗） pair meristems Bars = 50 mm im，inflorescence meristem v，vasculature（维管束）,spm，spikelet（副穗） pair meristems g, glume（花颖）Bars = 50 mm,8. vt2 spi1 Double Mutants Have a Slightly More Severe Phenotype Than vt2 Single Mutants,9. Auxin Levels in Single and Double Mutants,spi1 and vt2 mutants had an average 82%and 34% of normal IAA levels,10. vt2 and bif2 Exhibit a Synergistic Interaction,11. vt2 Is Epistatic to ba1,Quantification revealed that there was no statistically significant reduction in plant height or leaf number in vt2 ba1 double mutants compared with vt2 alone. ba1 mutants produce tassel inflorescences similar to those of vt2 mutants, ba1 tassels produce suppressed bract primordia（包原基） in regular rows along the rachis of the tassel. These bumps indicate pools of auxin that are produced and transported normally to the inflorescence but cannot be used to produce spikelets due to the absence of ba1 gene function.,Finally, ba1 mutants never produce ears since they lack the ability to initiate ear axillary meristems, and vt2 ba1 double mutants similarly never produced an ear shoot. These results illustrate that vt2 is completely epistatic to ba1 during both vegetative and tassel inflorescence development. As ba1 mutants do not produce ear shoots, ba1 is epistatic to vt2 during the production of the ear.,Discussion,Here, we show that the vt2 plays a significant role in axillary meristem formation during inflorescence development in maize. vt2 encodes an enzyme with similarity to TAA1, which has been demonstrated to convert Trp to IPA in Arabidopsis The IPA pathway for Trp-dependent auxin biosynthesis contributes significantly to vegetative and reproductive development in maize.,1.Auxin Biosynthesis Pathways in Maize and Arabidopsis,In Arabidopsis, the similarity of phenotype of yuc and taa multiple mutant combinations has been used as an argument to suggest that these two genes act in the same pathway for the production of auxin rather than being separate independent pathways vt2 spi1double mutants have a slightly more severe phenotype than the vt2single mutant does.vt2 spi1two genes may act in the same pathway.,2.The Role of Temperature in Auxin Biosynthesis,Maize vt2 mutants have a weaker inflorescence phenotype at high temperature,whereas some defects in Arabidopsis taa1 mutants can be detected only at high temperature. 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