气孔在光合作用作为农作物产量形成和在节水抗逆介导农作物稳产的基础生理过程中起重要作用。乙烯促进气孔发育，但是作用机制尚不清楚。本项目前期工作鉴定到一个磷酸酶基因OsSDY1，突变导致气孔密度增高、气孔导度和光合作用降低，造成水稻生长缓慢、开花延迟、稻穗和谷粒短小、结实率和千粒重降低以及黄化苗呈组成性乙烯反应，乙烯合成基因表达上调。我们因此提出假说：OsSDY1基因通过反调节相关激酶的磷酸化作用参与调控乙烯信号途径和气孔的发育，影响水稻生长和产量形成相关性状。本研究将结合全基因组关联分析、细胞生理与遗传分析、基因组编辑、定点突变、酵母双杂交以及磷酸化蛋白质组学等手段，筛选鉴定OsSDY1的作用底物、作用位点及对应的激酶；明确OsSDY1在气孔发育与乙烯信号途径中的位置及其在水稻抗逆反应中的作用；阐明OsSDY1调控气孔密度与乙烯途径的作用机制，为水稻高产、稳产育种奠定基础。

Plants tightly regulate stomatal development to control CO2 uptake and water exit therefore fine tuning the balance between photosynthesis and transpiration. We initiated this project to explore the possibility to breed “climate change ready” rice varieties with improved ecological adaptation and agricultural capacity by targeting stomata. Therefore, a genome-wide association study has been conducted to detect the genetic variants associated with stomatal density in rice. Then by developing and analyzing the genetic modified rice, we have successfully pinned down two genes likely involved in stomatal formation. In this proposal, we will focus on one of the genes which we called OsSDY1 for Oryza sativa Stomatal Density and Yield 1. OsSDY1 is widely expressed throughout the plant, and gel assays using recombinant OsSDY1 detected innate phosphatase activity, as with its counterpart in Arabidopsis, suggesting the involvement of OsSDY1 in phosphorylation-dephosphorylation reactions. OsSDY1 deficiency not only caused an increase in stomatal density, but also compromised several yield-related agronomic traits, including plant height, flowering time, grain size and 1000-grain weight. Intriguingly, dark-grown ossdy1 mutant seedlings showed a strong inhibited root growth but enhanced coleoptile elongation, reminiscent of the particular ethylene “double responses” of rice, suggesting ethylene pathway is over activated by the loss of function of OsSDY1. As a potent modulator of plant development and defense, ethylene has long been documented to be a positive regulator of stomatal formation though the molecular basis has remained largely unknown. Various protein kinases have been reported to play key roles in regulating both stomatal development (e.g. through phosphorylation of SPCH and YDA) and ethylene biosynthesis (e.g. through phosphorylation of ACS2 and ACS6) and signaling (e.g. through phosphorylation of EIN2, EIN3 and ERFs). In contrast, our knowledge of the phosphatases that counter-regulate kinase mediated phosphorylation to ensure fast regulation of signaling is very limited. In this study, we hypothesize that OsSDY1 regulates ethylene pathway, stomatal development and yield related agronomic traits in rice. To define the mechanism of OsSDY1 functions, we propose to combine molecular, biochemical, genetic, physiological and phosphoproteomics approaches to 1. examine the impact of OsSDY1 deficiency on rice responses to various biotic and abiotic factors; 2. identify the substrate, the dephosphorylation sites, and the partner kinase(s) of OsSDY1; 3. determine whether OsSDY1 regulates stomatal density and ethylene signalling pathway independently, or rather OsSDY1 regulates stomatal formation through ethylene action which in turn modulates rice growth and productivity. Knowledge gained during this study will provide essential insights into the regulatory mechanism of stomatal development and ethylene pathway in rice, which is key to breed rice varieties with improved photosynthetic adaptation to environmental change, and therefore to maintain or even enhance rice performance, yield, and productivity under adverse conditions.