The ANGUSTIFOLIA gene of Arabidopsis, a plant CtBP gene, regulates leaf-cell expansion, the arrangement of cortical microtubules in leaf cells and expression of a gene involved in cell-wall formation

We previously showed that the ANGUSTIFOLIA (AN) gene regulates the width of leaves of Arabidopsis thaliana, by controlling the polar elongation of leaf cells. In the present study, we found that the abnormal arrangement of cortical microtubules (MTs) in an leaf cells appeared to account entirely for the abnormal shape of the cells. It suggested that the AN gene might regulate the polarity of cell growth by controlling the arrangement of cortical MTs. We cloned the AN gene using a map-based strategy and identified it as the first member of the CtBP family to be found in plants. Wild-type AN cDNA reversed the narrow-leaved phenotype and the abnormal arrangement of cortical MTs of the an-1 mutation. In the animal kingdom, CtBPs self-associate and act as co-repressors of transcription. The AN protein can also self-associate in the yeast two-hybrid system. Furthermore, microarray analysis suggested that the AN gene might regulate the expression of certain genes, e.g. the gene involved in formation of cell walls, MERI5. A discussion of the molecular mechanisms involved in the leaf shape regulation is presented based on our observations.

本团队此前已证实，ANGUSTIFOLIA（AN）基因可通过调控拟南芥（Arabidopsis thaliana）叶片细胞的极性伸长，进而控制其叶宽。在本研究中，我们发现an突变体叶片细胞内的皮层微管（cortical microtubules, MTs）排列异常，这似乎完全解释了细胞形态异常的成因。上述结果表明，AN基因或可通过调控皮层微管的排列，控制细胞生长的极性。我们采用图位克隆策略分离得到AN基因，并证实其为植物中首个被发现的CtBP家族成员。野生型AN互补DNA（cDNA）可恢复an-1突变体的窄叶表型以及皮层微管排列异常的缺陷。在动物界中，CtBP蛋白可发生自身缔合，并作为转录共抑制因子发挥功能。酵母双杂交系统实验证实，AN蛋白同样可发生自身缔合。此外，微阵列（microarray）分析结果显示，AN基因或可调控部分基因的表达，例如参与细胞壁形成的MERI5基因。本研究基于上述观测结果，对叶形调控涉及的分子机制展开了讨论。