As a multigenic trait, rice tillering can optimize plant architecture for the maximum agronomic yield. SQUAMOSA PROMOTER BINDING PROTEIN-LIKE14 (OsSPL14) has been demonstrated to be necessary and sufficient to inhibit rice branching, but the underlying mechanism remains largely unclear. Here, we demonstrated that OsSPL14, which is cleaved by miR529 and miR156, inhibits tillering by fine-tuning auxin transport in rice. RNA interference of OsSPL14 or miR529 and miR156 overexpression significantly increased the tiller number, whereas OsSPL14 overexpression decreased the tiller number. Histological analysis revealed that the OsSPL14-overexpressing line had normal initiation of axillary buds but inhibited outgrowth of tillers. Moreover, OsSPL14 was found to be responsive to indole-acetic acid and 1-naphthylphthalamic acid, and RNA interference of OsSPL14 reduced polar auxin transport and increased 1-naphthylphthalamic acid sensitivity of rice plants. Further analysis revealed that OsSPL14 directly binds to the promoter of PIN-FORMED 1b (OsPIN1b) and PIN-LIKE6b (PILS6b) to regulate their expression positively. OsPIN1b and PILS6b were highly expressed in axillary buds and proved involved in bud outgrowth. Loss of function of OsPIN1b or PILS6b increased the tiller number of rice. Taken together, our findings suggested that OsSPL14 could control axillary bud outgrowth and tiller number by activating the expression of OsPIN1b and PILS6b to fine-tune auxin transport in rice.
水稻株型決定了水稻的產(chǎn)量、抗倒伏性等重要的農(nóng)藝性狀。培育具備適度分蘗、抗倒伏、營養(yǎng)高效的水稻品種是育種家的目標。OsSPL14編碼一個典型的含SBP-box域的轉(zhuǎn)錄因子，是近年來發(fā)現(xiàn)的具有理想株型形成潛力的重要控制基因。然而，其調(diào)控水稻株型的分子機理仍有待深入解析。袁文雅教授團隊通過分析OsSPL14基因干擾突變體和過表達植株的分蘗表型，結(jié)合側(cè)生分生組織的石蠟切片結(jié)果，證實受miR529和miR156調(diào)控的OsSPL14基因可通過抑制水稻分蘗芽的伸長，從而負調(diào)控水稻的分蘗數(shù)。體外激素施加實驗證實OsSPL14受到生長素的誘導，暗示其可能參與生長素信號相關的調(diào)控路徑。后續(xù)通過酵母單雜交、熒光素酶激活，凝膠阻滯及染色質(zhì)免疫共沉淀實驗，共同證實OsSPL14可結(jié)合在生長素運輸基因OsPIN1b和PILS6b的啟動子區(qū)域的GTAC順式作用元件上，激活其表達。研究進一步發(fā)現(xiàn)，OsSPL14基因可通過影響水稻地上部分的生長素極性運輸，從而影響水稻側(cè)生分生組織中的生長素分布，最終調(diào)節(jié)水稻分蘗芽的生長。該項發(fā)現(xiàn)提高了對miR529/156-OsSPL14模塊參與水稻激素間平衡，激素信號傳導和植物株型形態(tài)建成的理解。有助于解析產(chǎn)量相關基因OsSPL14復雜的調(diào)控網(wǎng)絡，為培育水稻理想株型品種奠定理論和應用基礎。