Institute of Plant Stress Adaptation and Genetic Enhancement, Zhejiang Normal University, Jinhua 321004, China.
Zhejiang Provincial Key Laboratory of Biotechnology on Specialty Economic Plants, Department of Biology, College of Chemistry and Life Sciences, Zhejiang Normal University, Jinhua 321004, China.
Plant Physiol. 2023 Jan 2;191(1):56-69. doi: 10.1093/plphys/kiac401.
Leaf angle is determined by lamina joint inclination and is an important agronomic trait that determines plant architecture, photosynthetic efficiency, and crop yield. Cytokinins (CKs) are phytohormones involved in shaping rice (Oryza sativa L.) architecture, but their role in leaf angle remains unknown. Here, we report that CK accumulation mediated by rice CK OXIDASE/DEHYDROGENASE3 (OsCKX3) controls lamina joint development and negatively regulates leaf angle. Phenotypic analysis showed that rice osckx3 mutants had smaller leaf angles, while the overexpression lines (OsCKX3-OE) had larger leaf angles. Histological sections indicated that the leaf inclination changes in the osckx3 and OsCKX3-OE lines resulted from asymmetric proliferation of the cells and vascular bundles in the lamina joint. Reverse transcription quantitative PCR, promoter-fused β-glucuronidase expression, and subcellular localization assays indicated that OsCKX3 was highly expressed in the lamina joint, and OsCKX3-GFP fusion protein localized to the endoplasmic reticulum. The enzyme assays using recombinant protein OsCKX3 revealed that OsCKX3 prefers trans-zeatin (tZ) and isopentenyladenine (iP). Consistently, tZ and iP levels increased in the osckx3 mutants but decreased in the OsCKX3 overexpression lines. Interestingly, agronomic trait analysis of the rice grown in the paddy field indicated that osckx3 displayed a smaller leaf angle and enhanced primary branch number, grain size, 1,000-grain weight, and flag leaf size. Collectively, our results revealed that enhancing CK levels in the lamina joint by disrupting OsCKX3 negatively regulates leaf angle, highlighting that the CK pathway can be engineered to reduce leaf angle in rice and possibly in other cereals.
叶片角度由叶片与茎之间的夹角决定，是决定植物形态、光合作用效率和作物产量的重要农艺性状。细胞分裂素（CKs）是参与水稻（Oryza sativa L.）形态建成的植物激素，但它们在叶片角度中的作用尚不清楚。在这里，我们报告说，由水稻细胞分裂素氧化酶/脱氢酶 3（OsCKX3）介导的细胞分裂素积累控制叶片与茎之间的夹角，并负调控叶片角度。表型分析表明，水稻 osckx3 突变体的叶片角度较小，而过表达系（OsCKX3-OE）的叶片角度较大。组织学切片表明，osckx3 和 OsCKX3-OE 系中叶片倾斜的变化是由于叶片与茎之间的细胞和维管束的不对称增殖所致。逆转录定量 PCR、启动子融合β-葡萄糖醛酸酶表达和亚细胞定位分析表明，OsCKX3 在叶片与茎之间高度表达，并且 OsCKX3-GFP 融合蛋白定位于内质网。使用重组蛋白 OsCKX3 的酶分析表明，OsCKX3 优先选择反式玉米素（tZ）和异戊烯基腺嘌呤（iP）。一致地，osckx3 突变体中的 tZ 和 iP 水平增加，而 OsCKX3 过表达系中的 tZ 和 iP 水平降低。有趣的是，在稻田中种植的水稻的农艺性状分析表明，osckx3 表现出较小的叶片角度和增强的一级分枝数、粒长、千粒重和旗叶大小。总之，我们的研究结果表明，通过破坏 OsCKX3 使叶片与茎之间的 CK 水平升高，负调控叶片角度，突出了 CK 途径可用于减少水稻和可能的其他谷类作物的叶片角度。
