Switching the direction of stem gravitropism by altering two amino acids in AtLAZY1

First author: Takeshi Yoshihara; Affiliations: University of Wisconsin (威斯康星大学): Madison, US

Corresponding author: Edgar P. Spalding

From germination to flowering, gravity influences plant growth and development. A rice (Oryza sativa) mutant with a distinctly prostrate growth habit led to the discovery of a gene category that participates in the shaping of plant form by gravity. Each so-called LAZY gene includes five short regions of conserved sequence. The importance of each of these regions in the LAZY1 gene of Arabidopsis thaliana (AtLAZY1) was tested by mutating each region and measuring how well transgenic expression of the resulting protein variant rescued the large inflorescence branch angle of an atlazy1 mutant. The effect of each alteration on subcellular localization was also determined. Region I was required for AtLAZY1 to reside at the plasma membrane, which is necessary for its function. Mutating region V severely disrupted function without affecting subcellular localization. Regions III and IV could be mutated without large impacts on function or localization. Altering region II with two conservative amino acid substitutions (L92A/I94A) had the profound effect of switching shoot gravity responses from negative (upward bending) to positive (downward bending), resulting in a 'weeping' inflorescence phenotype. Mechanical weakness of the stem was ruled out as an explanation for the downward bending. Instead, experiments demonstrated that the L92A/I94A change to AtLAZY1 reversed the auxin gradient normally established across stems by the gravity-sensing mechanism. This discovery opens up new avenues for studying how auxin gradients form across organs and new approaches for engineering plant architecture for agronomic and other practical purposes.

从发芽到开花，重力影响着植物生长和发育的方方面面。一个具有明显伏倒生长习性的水稻突变体导致了一类基因的发现，这类基因参与重力对于植物形态的塑造。这类基因叫做LAZY基因，包含5个保守的短序列。作者通过分别突变每一个短序列测试了拟南芥LAZY1基因中这5段序列的重要性，并将每一个突变转入到atlazy1突变体中，测量了其对于该突变体主花序分枝角度缺陷的拯救情况。作者确定了每一个序列区域对于该蛋白的亚细胞定位的影响。区域I对于AtLAZY1定位于质膜上是必要的，从而对于其正常发挥功能也是必要的。而突变区域V能够在不影响亚细胞定位的情况下严重扰乱其蛋白功能。区域III和IV的突变对于该蛋白的亚细胞定位和功能都没有太大的影响。而将区域II两个保守位置上的氨基酸突变掉（L92A/I94A）能够将茎的重力响应从负向（向上弯曲）转变为正向（向下弯曲），导致一个“下垂”的花序表型。作者通过试验排除了花序茎杆的机械缺陷导致花序向下弯曲的可能性。相反，进一步的试验显示AtLAZY1蛋白上L92A/I94A的氨基酸替换反转了茎中由重力感应机制建立的生长素梯度。这项研究的发现为研究跨器官的生长素梯度如何形成开辟了新途径，并为以农艺和其他实际应用为目的的植物结构遗传改造提供了新的方法。

通讯：Edgar P. Spalding (https://botany.wisc.edu/staff/spalding-edgar-p/)

个人简介：1990年，宾夕法尼亚州立大学，博士。

研究方向：光、重力、温度和其他变量对于种子休眠胚成功发芽的作用。

doi: https://doi.org/10.1104/pp.19.01144

Journal: Plant Physiology

First Published: December 09, 2019