Zhang Ying, Bergmann Dominique C, Dong Juan
Waksman Institute of Microbiology, Rutgers, The State University of New Jersey, Piscataway, NJ 08854, USA.
Department of Biology, 371 Serra Mall, Stanford University, Stanford, CA 94305-5020, USA HHMI, Stanford University, Stanford, CA 94305-5020, USA
J Exp Bot. 2016 Sep;67(17):5093-103. doi: 10.1093/jxb/erw274. Epub 2016 Jul 15.
Cell polarity is a prerequisite for asymmetric cell divisions (ACDs) that generate cell type diversity during development of multicellular organisms. In Arabidopsis, stomatal lineage ACDs are regulated by the plant-specific protein BREAKING OF ASYMMETRY IN THE STOMATAL LINEAGE (BASL). BASL exhibits dynamic subcellular localization, accumulating initially in the nucleus, but then additionally in a highly polarized crescent at the cell cortex before division. BASL polarization requires a phosphorylation-mediated activation process, but how this is achieved remains unknown. In this study, we performed a fine-scale dissection of BASL protein subdomains and elucidated a nuclear localization sequence for nuclear import and a critical FxFP motif for cortical polarity formation, respectively. Artificially tethering BASL subdomains to the plasma membrane suggests that novel protein partner/s might exist and bind to an internal region of BASL. In addition, we suspect the existence of a protein degradation mechanism associated with the amino terminal domain of BASL that accounts for restricting its predominant expression to the stomatal lineage cells of the epidermis. Taken together, our results revealed that BASL, through its distinct subdomains, integrates multiple regulatory inputs to provide a mechanism that promotes difference during stomatal lineage ACDs.
细胞极性是多细胞生物发育过程中产生细胞类型多样性的不对称细胞分裂（ACD）的前提条件。在拟南芥中，气孔谱系ACD受植物特异性蛋白气孔谱系不对称性打破（BASL）调控。BASL表现出动态亚细胞定位，最初在细胞核中积累，随后在分裂前额外在细胞皮层的高度极化新月区积累。BASL极化需要磷酸化介导的激活过程，但具体实现方式尚不清楚。在本研究中，我们对BASL蛋白亚结构域进行了精细剖析，分别阐明了用于核输入的核定位序列和用于皮层极性形成的关键FxFP基序。将BASL亚结构域人工拴系到质膜表明可能存在新的蛋白质伴侣并与BASL的内部区域结合。此外，我们怀疑存在一种与BASL氨基末端结构域相关的蛋白质降解机制，该机制导致其主要在表皮的气孔谱系细胞中表达。综上所述，我们的结果表明，BASL通过其独特的亚结构域整合多种调控输入，提供了一种在气孔谱系ACD过程中促进差异的机制。
