Environmental and auxin regulation of wood formation involves members of the Aux/IAA gene family in hybrid aspen

Indole acetic acid (IAA/auxin) profoundly affects wood formation but the molecular mechanism of auxin action in this process remains poorly understood. We have cloned cDNAs for eight members of the Aux/IAA gene family from hybrid aspen (Populus tremula L. x Populus tremuloides Michx.) that encode potential mediators of the auxin signal transduction pathway. These genes designated as PttIAA1-PttIAA8 are auxin inducible but differ in their requirement of de novo protein synthesis for auxin induction. The auxin induction of the PttIAA genes is also developmentally controlled as evidenced by the loss of their auxin inducibility during leaf maturation. The PttIAA genes are differentially expressed in the cell types of a developmental gradient comprising the wood-forming tissues. Interestingly, the expression of the PttIAA genes is downregulated during transition of the active cambium into dormancy, a process in which meristematic cells of the cambium lose their sensitivity to auxin. Auxin-regulated developmental reprogramming of wood formation during the induction of tension wood is accompanied by changes in the expression of PttIAA genes. The distinct tissue-specific expression patterns of the auxin inducible PttIAA genes in the cambial region together with the change in expression during dormancy transition and tension wood formation suggest a role for these genes in mediating cambial responses to auxin and xylem development.     

The diageotropica mutation alters auxin induction of a subset of the Aux/IAA gene family in tomato

The diageotropica (dgt) mutation has been proposed to affect either auxin perception or responsiveness in tomato plants. It has previously been demonstrated that the expression of one member of the Aux/IAA family of auxin-regulated genes is reduced in dgt plants. Here, we report the cloning of ten new members of the tomato Aux/IAA family by PCR amplification based on conserved protein domains. All of the gene family members except one (LeIAA7) are expressed in etiolated tomato seedlings, although they demonstrate tissue specificity (e.g. increased expression in hypocotyls vs. roots) within the seedling. The wild-type auxin-response characteristics of the expression of these tomato LeIAA genes are similar to those previously described for Aux/IAA family members in Arabidopsis. In dgt seedlings, auxin stimulation of gene expression was reduced in only a subset of LeIAA genes (LeIAA5, 8, 10, and 11), with the greatest reduction associated with those genes with the strongest wild-type response to auxin. The remaining LeIAA genes tested exhibited essentially the same induction levels in response to the hormone in both dgt and wild-type hypocotyls. These results confirm that dgt plants can perceive auxin and suggest that a specific step in early auxin signal transduction is disrupted by the dgt mutation.     

中国科学家在生长素信号转导领域取得突破性研究进展

生长素(IAA)作为一种重要的植物激素, 参与调节植物生长发育的许多过程, 其作用机理长期以来备受人们的关注。最近, 中国科学家在生长素信号转导的分子机理研究领域取得了突破性进展。     

植物生长素反应因子研究进展

生长素反应因子（ARFs）是植物生长和发育的重要调节因子,在生长素早期反应蛋白（Aux／IAAs）的参与下,通过和生长素反应基因启动子区AuxRE元件的JTGTCTC序列结合,共同调控这些基因的表达。近年来关于生长素反应因子的分子结构和ARF与Aux／IAA的相互作用及其对植物生长和发育的影响、作用的靶基因以及分子机制受到人们的重视,并在这些方面做了大量的研究。     

Production and characterization of auxin-insensitive rice by overexpression of a mutagenized rice IAA protein

Since auxin was first isolated and characterized as a plant hormone, the underlying molecular mechanism of auxin signaling has been elucidated primarily in dicot plants represented by Arabidopsis. In monocot plants, the molecular mechanism of auxin signaling has remained unclear, despite various physiological experiments. To understand the function and mechanism of auxin signaling in rice ( Oryza sativa ), we focused on the IAA gene, a well-studied gene in Arabidopsis that serves as a negative regulator of auxin signaling. We found 24 IAA gene family members in the rice genome. OsIAA3 is one of these family members whose expression is rapidly increased in response to auxin. We produced transgenic rice harboring m OsIAA3 - GR , which can overproduce mutant OsIAA3 protein containing an amino acid change in domain II to cause a gain-of-function phenotype, by treatment with dexamethasone. The transgenic rice was insensitive to auxin and gravitropic stimuli, and exhibited short leaf blades, reduced crown root formation, and abnormal leaf formation. These results suggest that , in rice, auxin is important for development and its signaling is mediated by IAA genes.