Graduate School of Life Sciences, Tohoku University, Sendai 980-8577, Japan.
College of Agriculture, Nanjing Agricultural University, Nanjing 210095, China.
Plant Physiol. 2022 Aug 1;189(4):2210-2226. doi: 10.1093/plphys/kiac216.
At the transition from vegetative to reproductive growth in rice (Oryza sativa), a developmental program change occurs, resulting in panicle (rice inflorescence) formation. The initial event of the transition is the change of the shoot apical meristem to an inflorescence meristem (IM), accompanied by a rapid increase in the meristem size. Suppression of leaf growth also occurs, resulting in the formation of bracts. The IM generates branch meristems (BMs), indeterminate meristems that reiteratively generate next-order meristems. All meristems eventually acquire a determinate spikelet meristem identity and terminate after producing a floret. ABERRANT PANICLE ORGANIZATION2 (APO2) is the rice ortholog of Arabidopsis (Arabidopsis thaliana) LEAFY (LFY), a plant-specific transcription factor (TF). APO2 is a positive regulator of panicle branch formation. Here, we show that APO2 is also required to increase the meristem size of the IM and suppress bract outgrowth. We identified genes directly and indirectly regulated by APO2 and identified APO2-binding sites. These analyses showed that APO2 directly controls known regulators of panicle development, including SQUAMOSA PROMOTER BINDING PROTEIN LIKE14 and NECK LEAF1. Furthermore, we revealed that a set of genes act as downstream regulators of APO2 in controlling meristem cell proliferation during reproductive transition, bract suppression, and panicle branch formation. Our findings indicate that APO2 acts as a master regulator of rice panicle development by regulating multiple steps in the reproductive transition through directly controlling a set of genes.
在水稻（Oryza sativa）从营养生长向生殖生长的转变过程中，发生了发育程序的改变，导致了穗（水稻花序）的形成。转变的初始事件是茎尖分生组织转变为花序分生组织（IM），同时分生组织的大小迅速增加。叶片生长也受到抑制，导致苞片的形成。IM 产生分枝分生组织（BMs），不定分生组织反复产生下一阶的分生组织。所有的分生组织最终获得一个有定数的小穗分生组织身份，并在产生一个小花后终止。异常穗器官组织 2（APO2）是水稻的拟南芥（Arabidopsis thaliana）LFY 的同源物，LFY 是一种植物特有的转录因子（TF）。APO2 是穗分枝形成的正调控因子。在这里，我们表明 APO2 也需要增加 IM 的分生组织大小并抑制苞片的生长。我们鉴定了直接和间接受 APO2 调控的基因，并鉴定了 APO2 结合位点。这些分析表明，APO2 直接控制已知的花序发育调节剂，包括 SQUAMOSA PROMOTER BINDING PROTEIN LIKE14 和 NECK LEAF1。此外，我们揭示了一组基因作为 APO2 的下游调节剂，在生殖转变过程中控制分生组织细胞增殖、苞片抑制和穗分枝形成。我们的研究结果表明，APO2 通过直接控制一组基因，在生殖转变过程中调节多个步骤，作为水稻穗发育的主调控因子。
