microRNA166 monitors SPOROCYTELESS/NOZZLE (SPL/NZZ) for building of the anther internal boundary

First author: Xiaorong Li; Affiliations: CAS Shanghai Institute of Plant Physiology and Ecology (中科院上海植物生理生态研究所): Shanghai, China

Corresponding author: Yuke He

The internal boundary between inner and outer microsporangia (小孢子囊) within anthers is essential for male fertility of vascular plants. Dehiscence zones embedded in the boundary release pollen for fertilization. However, the molecular mechanism underlying boundary formation in anthers remains poorly understood. Here, we report that microRNA166 (miR166) and its target PHABULOSA (PHB) regulate SPOROCYTELESS/NOZZLE (SPL/NZZ), which controls microsporogenesis. In developing anthers of Arabidopsis (Arabidopsis thaliana), the expression domains of miR165/6 and SPL/NZZ are overlapped and rearranged synchronously. Dominant mutation of PHB suppresses SPL/NZZ expression in the adaxial sides of stamens, resulting in a thickened boundary whereas activation of MIR166g upregulates SPL/NZZ expression, leading to ectopic microsporogenesis in the boundary. PHB limits the expression domains of SPL/NZZ to facilitate construction of the boundary while miR166 preserves the expression domains of SPL/NZZ by inhibiting PHB to allow the inner microsporangia to take shape. Subsequently, PHB activates key stem cell maintainer WUSCHEL (WUS) in anthers to restrict the stomium cells to the boundary so that dehiscence zones develop and release pollens properly. These findings link adaxial/abaxial polarity to microsporogenesis in building of the internal boundary of anthers, and thus advance the concepts underlying establishment of internal structure of male organs.

花药中小孢子囊内部和外部界限对于维管植物的雄性育性至关重要。边界区的开裂能够释放花粉，用于植物受精作用。然而，目前我们对于花药中边界形成的分子机制还不够了解。本文中，作者报道了miR166及其靶基因PHB调控SPL/NZZ，从而调控小孢子发生。在拟南芥正在发育中的花粉中，miR165/6和SPL/NZZ的表达区域重叠，并且同步改变。PHB的显性突变会抑制SPL/NZZ在雄蕊近轴处的表达，导致边界加厚；而MIR166g的激活会导致SPL/NZZ的上调表达，导致边界处的异位小孢子发生。PHB限制SPL/NZZ的表达从而加速边界的构建，而miR166通过抑制PHB保证SPL/NZZ的表达区域使得内层的小孢子囊能够发育成形。随后，PHB激活花药中关键干细胞维持基因WUS的表达，从而将花药裂口细胞局限在边界区，从而保证开裂区的正常发育以及后期花粉的正确释放。本文的发现将近轴/远轴极性与小孢子发生联系到一起，共建花药的内部边界，揭示了植物雄性器官内部结构建立的潜在分子机制。

通讯：何玉科 (http://www.sippe.ac.cn/sourcedb_sippe/zw/zjrc/201812/t20181219_5218253.html)

个人简介：1981年，西北农业大学，学士；1984年，西北农业大学，硕士；1986-1988年，荷兰园艺植物育种研究所，进修；1991年，兰州大学，博士；1991-1993年，中科院上海植物生理研究所，博士后。

研究方向：研究双链RNA结合蛋白基因HYL1和BcpLH控制下miRNA的合成及其基因沉默机理，microRNA指导下植物极性基因、生长素响应因子和细胞分裂基因调节叶片卷曲和花序变态的分子机理，解析大白菜和甘蓝等芸薹属植物叶卷曲和花序变态的遗传机制。

doi: https://doi.org/10.1104/pp.19.00336

Journal: Plant Physiology

First Published: June 27, 2019