Two branching strategies are exhibited in crops: enhanced apical dominance, as in maize, or weak apical dominance, as in rice. However, the underlying mechanism of weak apical dominance remains elusive. OsWUS, an ortholog of Arabidopsis WUSCHEL (WUS) in rice, is required for tiller development. In this study, we identified and functionally characterized a low‐tillering mutant decreased culm number 1 (dc1) that resulted from loss‐of‐function of OsWUS. The dc1 tiller buds are viable but repressed by the main culm apex, leading to stronger apical dominance than that of the wild type. Auxin response is enhanced in the dc1 mutant and knocking out the auxin action‐associated gene ABERRANT SPIKELET AND PANICLE 1 (ASP1) de‐repressed growth of the tiller buds in the dc1 mutant, suggesting that OsWUS and ASP1 are both involved in outgrowth of the rice tiller bud. Decapitation triggers higher contents of cytokinins in the shoot base of the dc1 mutant compared with those in the wild type, and exogenous application of cytokinin is not sufficient for sustained growth of the dc1 tiller bud. Transcriptome analysis indicated that expression levels of transcription factors putatively bound by ORYZA SATIVA HOMEOBOX 1 (OSH1) are changed in response to decapitation and display a greater fold change in the dc1 mutant than that in the wild type. Collectively, these findings reveal an important role of OsWUS in tiller bud growth by influencing apical dominance and provide the basis for an improved understanding of tiller bud development in rice.
自然界中，禾本科作物通常存在兩種分枝策略：單稈或少分蘗的強(qiáng)頂端優(yōu)勢，如玉米、高粱等；主莖與分蘗無顯著差別的弱頂端優(yōu)勢，如小麥、水稻等。兩種分枝類型都是決定作物產(chǎn)量的重要因素。研究表明，TCP轉(zhuǎn)錄因子TB1 (TEOSINTE BRANCHED 1) 是決定栽培玉米強(qiáng)頂端優(yōu)勢的關(guān)鍵因子。然而，決定水稻等弱頂端優(yōu)勢的因子仍未知。
OsWUS在水稻弱頂端優(yōu)勢中發(fā)揮重要功能。OsWUS，也稱MOC3/TAB1/SRT1(MONOCULM3/TILLERS ABSENT1/STERILE AND REDUCED TILLERING1)，是擬南芥分生組織干細(xì)胞維持關(guān)鍵基因WUS(WUSCHEL)在水稻中的同源基因，對水稻分蘗芽的形成和生長起重要作用。OsWUS功能缺失突變體dc1 (decreased culm number 1)，表現(xiàn)出分蘗數(shù)目減少、穗部小花畸形和雌不育的表型。深入研究表明，dc1分蘗芽生長受主莖顯著抑制，表現(xiàn)出生長素響應(yīng)和頂端優(yōu)勢增強(qiáng)的表型；分蘗期去除dc1主莖頂端或敲除生長素作用相關(guān)基因ASP1 (ABERRANT SPIKELET AND PANICLE1) 能夠解除主莖對分蘗芽的抑制，從而促進(jìn)分蘗芽的生長；通過對野生型和dc1去頂前后轉(zhuǎn)錄組比較分析發(fā)現(xiàn)，去頂對dc1突變體轉(zhuǎn)錄調(diào)控的影響顯著高于野生型；進(jìn)一步轉(zhuǎn)錄調(diào)控網(wǎng)絡(luò)預(yù)測發(fā)現(xiàn)，去頂會顯著影響dc1突變體中分生組織關(guān)鍵因子OSH1 (ORYZA SATIVA HOMEOBOX1)下游靶轉(zhuǎn)錄因子的表達(dá)，暗示OsWUS與OSH1轉(zhuǎn)錄調(diào)控網(wǎng)絡(luò)存在未知的分子連接。綜上，本研究揭示了OsWUS通過影響頂端優(yōu)勢促進(jìn)分蘗芽生長的分子機(jī)制，提高了人們對水稻分蘗發(fā)育機(jī)理的認(rèn)識。