水稻籽粒数是一个对粮食产量有很大贡献的农艺性状。 在水稻(Oryza Sativa)中，OsMKKK10-OsMKK4-OsMPK6级联反应受双特异性磷酸酶GSN1负调控，协调籽粒数和籽粒大小之间的权衡。 然而，GSN1-MAPK模块上下游调节每穗粒数的具体成分仍然不清楚。
在这里，我们报道了ERECTA1(OsER1)，每穗粒数的负调控因子，作用于OsMKKK10-OsMKK4-OsMPK6级联的上游，并且OsER1-OsMKKK10-OsMKK4-OsMPK6途径是维持细胞分裂素稳态所必需的。
OsMPK6直接与锌指转录因子DST相互作用并磷酸化，增强其对细胞分裂素OXIDASE2(OsCKX2)的转录激活，表明OsER1-OsMKKK10-OsMKK4-OsMPK6途径通过调节细胞分裂素代谢而形成穗部形态。
此外，DST或OsCKX2的过表达挽救了oser1、osmkk10、osmkk4和osmpk6突变体的小穗数表型，表明DST-OsCKX2模块位于OsER1-OsMKKK10-OsMKK4-OsMPK6遗传通路的下游。
这些发现揭示了MAPK信号通路和细胞分裂素代谢之间的特定crosstalk，揭示了发育信号如何调节植物激素稳态来塑造花序。
Abstract:
Grain number is a flexible trait that strongly contributes to grain yield. In rice (Oryza sativa), the OsMKKK10-OsMKK4-OsMPK6 cascade, which is negatively regulated by the dual-specificity phosphatase GSN1, coordinates the trade-off between grain number and grain size. However, the specific components upstream and downstream of the GSN1-MAPK module that regulate spikelet number per panicle remain obscure. Here, we report that ERECTA1 (OsER1), a negative regulator of spikelet number per panicle, acts upstream of the OsMKKK10-OsMKK4-OsMPK6 cascade and that the OsER1-OsMKKK10-OsMKK4-OsMPK6 pathway is required to maintain cytokinin homeostasis. OsMPK6 directly interacts with and phosphorylates the zinc finger transcription factor DST to enhance its transcriptional activation of CYTOKININ OXIDASE2 (OsCKX2), indicating that the OsER1-OsMKKK10-OsMKK4-OsMPK6 pathway shapes panicle morphology by regulating cytokinin metabolism. Furthermore, overexpression of either DST or OsCKX2 rescued the spikelet number phenotype of the oser1, osmkkk10, osmkk4, and osmpk6 mutants, suggesting that the DST-OsCKX2 module genetically functions downstream of the OsER1-OsMKKK10-OsMKK4-OsMPK6 pathway. These findings reveal specific crosstalk between a MAPK signaling pathway and cytokinin metabolism, shedding light on how developmental signals modulate phytohormone homeostasis to shape the inflorescence.
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