The phytohormone cytokinin (CK) positively regulates the activity and function of the shoot apical meristem (SAM), which is a major parameter determining seed production. The rice (Oryza sativa L.) Gn1a/OsCKX2 (Grain number 1a/Cytokinin oxidase 2) gene, which encodes a cytokinin oxidase, has been identified as a major quantitative trait locus contributing to grain number improvement in rice breeding practice. However, the molecular mechanism of how the expression of OsCKX2 is regulated in planta remains elusive. Here, we report that the zinc finger transcription factor DROUGHT AND SALT TOLERANCE (DST) directly regulates OsCKX2 expression in the reproductive meristem. DST-directed expression of OsCKX2 regulates CK accumulation in the SAM and, therefore, controls the number of the reproductive organs. We identify that DSTreg1, a semidominant allele of the DST gene, perturbs DST-directed regulation of OsCKX2 expression and elevates CK levels in the reproductive SAM, leading to increased meristem activity, enhanced panicle branching, and a consequent increase of grain number. Importantly, the DSTreg1 allele provides an approach to pyramid the Gn1a-dependent and Gn1a-independent effects on grain production. Our study reveals that, as a unique regulator of reproductive meristem activity, DST may be explored to facilitate the genetic enhancement of grain production in rice and other small grain cereals.
植物激素細胞分裂素（CK）的正調(diào)控莖端分生組織（SAM）的活性和功能，這是決定種子產(chǎn)量的主要參數(shù)。水稻Gn1a/OsCKX2（穗粒數(shù)1a/細胞分裂素氧化酶2）基因，編碼細胞分裂素氧化酶，在水稻育種實踐中已被確定為一個能提高籽粒數(shù)的主要數(shù)量性狀基因。然而，我們對植物中OsCKX2表達如何受調(diào)控的分子機制還不是很清楚。本文中，我們報道了鋅指轉(zhuǎn)錄因子“抗旱和耐鹽（DST）蛋白”能在生殖分生組織中直接調(diào)控OsCKX2的表達。DST直接調(diào)控下的OsCKX2表達能調(diào)控CK在SAM（莖端分生組織）區(qū)的積累，因此能控制生殖器官的數(shù)目。DSTreg1是一個半顯性等位基因，它破壞了DST對OsCKX2表達的調(diào)控并提高了CK在生殖期SAM的含量，導(dǎo)致了分生組織活性和穗枝梗數(shù)目的增加，籽粒數(shù)從而隨之增加。重要的是，該DSTreg1等位基因能被利用在依賴Gn1a和不依賴Gn1a增加谷粒產(chǎn)量的聚合育種基因利用中。綜上所述，我們認為DST作為一個獨立的調(diào)控生殖分生組織活性的調(diào)節(jié)因子，它可被開發(fā)利用在水稻和其他谷粒作物上遺傳改良谷粒產(chǎn)量。