The Waksman Institute of Microbiology, Rutgers, the State University of New Jersey; Piscataway, New Jersey, United States of America.
Department of Plant Biology, Rutgers, the State University of New Jersey, New Brunswick, New Jersey, United States of America.
PLoS Genet. 2020 Apr 2;16(4):e1008706. doi: 10.1371/journal.pgen.1008706. eCollection 2020 Apr.
Stomata are specialized pores in the epidermis of the aerial parts of a plant, where stomatal guard cells close and open to regulate gas exchange with the atmosphere and restrict excessive water vapor from the plant. The production and patterning of the stomatal lineage cells in higher plants are influenced by the activities of the widely-used mitogen-activated protein kinase (MAPK) signaling components. The phenotype caused by the loss-of-function mutations suggested pivotal roles of the canonical MAPK pathway in the suppression of stomatal formation and regulation of stomatal patterning in Arabidopsis, whilst the cell type-specific manipulation of individual MAPK components revealed the existence of a positive impact on stomatal production. Among a large number of putative MAPK substrates in plants, the nuclear transcription factors SPEECHLESS (SPCH) and SCREAM (SCRM) are targets of MAPK 3 and 6 (MPK3/6) in the inhibition of stomatal formation. The polarity protein BREAKING OF ASYMMETRY IN THE STOMATAL LINEAGE (BASL) is phosphorylated by MPK3/6 for localization and function in driving divisional asymmetries. Here, by functionally characterizing three MAPK SUBSTRATES IN THE STOMATAL LINEAGE (MASS) proteins, we establish that they are plasma membrane-associated, positive regulators of stomatal production. MPK6 can phosphorylate the MASS proteins in vitro and mutating the putative substrate sites interferes the subcellular partition and function of MASS in planta. Our fine-scale domain analyses identify critical subdomains of MASS2 required for specific subcellular localization and biological function, respectively. Furthermore, our data indicate that the MASS proteins may directly interact with the MAPKK Kinase YODA (YDA) at the plasma membrane. Thus, the deeply conserved MASS proteins are tightly connected with MAPK signaling in Arabidopsis to fine-tune stomatal production and patterning, providing a functional divergence of the YDA-MPK3/6 cascade in the regulation of plant developmental processes.
气孔是植物地上部分表皮中的特化孔，气孔保卫细胞通过关闭和开放来调节与大气的气体交换，并限制植物中过多的水蒸气。高等植物中气孔谱系细胞的产生和模式形成受到广泛使用的丝裂原活化蛋白激酶 (MAPK) 信号成分的活性的影响。功能丧失突变引起的表型表明，经典 MAPK 途径在抑制气孔形成和调节拟南芥气孔模式方面起着关键作用，而单个 MAPK 成分的细胞类型特异性操作揭示了其对气孔产生的积极影响。在植物中大量假定的 MAPK 底物中，核转录因子 SPEECHLESS (SPCH) 和 SCREAM (SCRM) 是 MAPK 3 和 6 (MPK3/6) 在抑制气孔形成中的靶标。极性蛋白 BREAKING OF ASYMMETRY IN THE STOMATAL LINEAGE (BASL) 通过 MPK3/6 磷酸化，定位于并驱动分裂不对称性，从而发挥作用。在这里，通过对三个 MAPK SUBSTRATES IN THE STOMATAL LINEAGE (MASS) 蛋白的功能进行表征，我们确定它们是质膜相关的，是气孔产生的正调节剂。MPK6 可以在体外磷酸化 MASS 蛋白，并且突变假定的底物位点会干扰 MASS 在植物体内的亚细胞分区和功能。我们的精细结构域分析确定了 MASS2 所需的关键亚域，分别用于特定的亚细胞定位和生物学功能。此外，我们的数据表明，MASS 蛋白可能直接在质膜上与 MAPKK 激酶 YODA (YDA) 相互作用。因此，在拟南芥中，高度保守的 MASS 蛋白与 MAPK 信号紧密相连，以精细调节气孔的产生和模式形成，为 YDA-MPK3/6 级联在植物发育过程中的调节提供了功能上的差异。
