Ku Su-Jin, Park Jin-Young, Ha Suk-Bong, Kim Jungmook
Department of Plant Biotechnology, Agricultural Plant Stress Research Center and Biotechnology Research Institute, Chonnam National University, Puk-Gu, Gwangju, Republic of Korea.
J Plant Physiol. 2009 Mar 15;166(5):548-53. doi: 10.1016/j.jplph.2008.07.006. Epub 2008 Sep 3.
The auxin/indoleacetic acid (Aux/IAA) proteins are negative regulators of the auxin response factors (ARFs) that regulate expression of auxin-responsive genes. The Aux/IAA proteins have four conserved domains. Domain II is responsible for the rapid degradation of these proteins. Degradation of the Aux/IAA proteins, mediated by a SCF(TIR1) E3 ubiquitin protein ligase complex, is critical for auxin-regulated gene expression. Using a steroid-hormone-inducible system, we had previously shown that a protein-stability-enhancing mutation in domain II of IAA1 (iaa1) impaired diverse auxin responses. Inhibition of hypocotyl elongation, leaf expansion, and stem elongation by overexpression of iaa1 suggested that cell enlargement and/or cell division might be affected. We here examined the effects of the domain II mutation on cellular anatomy using light microscopy. Our results show that overexpression of iaa1 in Arabidopsis significantly reduced cell length and cell number and affected cell shape in inflorescences and leaves in a dexamethasone (DEX)-dependent manner. These results suggest that IAA1 might be involved in cell elongation as well as in cell division in the aerial parts of Arabidopsis plants. In addition, the formation of both phloem and xylem in leaves and stems was also impaired in a DEX-dependent manner, indicating a potential involvement of IAA1 in vascular development.
生长素/吲哚乙酸（Aux/IAA）蛋白是生长素响应因子（ARF）的负调控因子，而ARF可调控生长素响应基因的表达。Aux/IAA蛋白有四个保守结构域。结构域II负责这些蛋白的快速降解。由SCF(TIR1) E3泛素蛋白连接酶复合体介导的Aux/IAA蛋白降解，对于生长素调控的基因表达至关重要。利用类固醇激素诱导系统，我们之前已表明IAA1（iaa1）结构域II中的一个增强蛋白稳定性的突变会损害多种生长素响应。iaa1过表达对下胚轴伸长、叶片扩展和茎伸长的抑制表明，细胞增大和/或细胞分裂可能受到影响。我们在此使用光学显微镜检查了结构域II突变对细胞解剖结构的影响。我们的结果表明，拟南芥中iaa1的过表达以地塞米松（DEX）依赖的方式显著降低了花序和叶片中的细胞长度和细胞数量，并影响了细胞形状。这些结果表明，IAA1可能参与拟南芥地上部分的细胞伸长以及细胞分裂。此外，叶片和茎中韧皮部和木质部的形成也以DEX依赖的方式受损，表明IAA1可能参与维管发育。
