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.
粒數(shù)是影響籽粒產(chǎn)量的一個彈性性狀。在水稻中，OsMKKK10-OsMKK4-OsMPK6級聯(lián)受到雙特異性磷酸酶GSN1的負調(diào)控，協(xié)調(diào)粒數(shù)和粒徑大小的平衡。然而，GSN1-MAPK模塊上游和下游調(diào)控每穗穎花數(shù)的具體成分仍然不清楚。在這里，我們報道了ERECTA1（OsER1），一個每穗穎花數(shù)的負調(diào)節(jié)因子，作用于OsMKKK10-OsMKK4-OsMPK6級聯(lián)的上游，并且OsER1-OsMKKK10-OsMKK4-OsMPK6通路是維持細胞分裂素穩(wěn)態(tài)所必需的。OsMPK6直接與鋅指轉(zhuǎn)錄因子DST相互作用并磷酸化，增強其對細胞分裂素氧化酶OsCKX2的轉(zhuǎn)錄激活，表明OsER1-OsMKKK10-OsMKK4-OsMPK6通路通過調(diào)節(jié)細胞分裂素代謝而形成穗部形態(tài)。此外，DST或OsCKX2的過度表達挽救了oser1、osmkkk10、osmkkk4和osmpk6突變體的小穗數(shù)表型，這表明DST-OsCKX2模塊作用于OsER1-OsMKKK10-OsMKK4-OsMPK6途徑下游。這些發(fā)現(xiàn)揭示了MAPK信號通路和細胞分裂素代謝之間的特定串?dāng)_，揭示了發(fā)育信號如何調(diào)節(jié)植物激素內(nèi)穩(wěn)態(tài)來塑造花序。