Mo Tianyu, Wang Tianhao, Sun Yinglu, Kumar Ashmit, Mkumbwa Humphrey, Fang Jingjing, Zhao Jinfeng, Yuan Shoujiang, Li Zichao, Li Xueyong
State Key Laboratory of Crop Gene Resources and Breeding, National Key Facility for Crop Gene Resources and Genetic Improvement, Institute of Crop Sciences, Chinese Academy of Agricultural Sciences, Beijing 100081, China; Beijing Key Laboratory of Crop Genetic Improvement, College of Agronomy and Biotechnology, China Agricultural University, Beijing 100193, China.
State Key Laboratory of Crop Gene Resources and Breeding, National Key Facility for Crop Gene Resources and Genetic Improvement, Institute of Crop Sciences, Chinese Academy of Agricultural Sciences, Beijing 100081, China.
Plant Commun. 2024 Dec 9;5(12):101073. doi: 10.1016/j.xplc.2024.101073. Epub 2024 Aug 28.
As an important yield component, rice tiller number controls panicle number and determines grain yield. Regulation of rice tiller number by chloroplast pentatricopeptide repeat (PPR) proteins has not been reported previously. Here, we report the rice reduced culm number22 (rcn22) mutant, which produces few tillers owing to suppressed tiller bud elongation. Map-based cloning revealed that RCN22 encodes a chloroplast-localized P-type PPR protein. We found that RCN22 specifically binds to the 5' UTR of RbcL mRNA (encoding the large subunit of Rubisco) and enhances its stability. The reduced abundance of RbcL mRNA in rcn22 leads to a lower photosynthetic rate and decreased sugar levels. Consequently, transcript levels of DWARF3 (D3) and TEOSINTE BRANCHED1 (TB1) (which encode negative regulators of tiller bud elongation) are increased, whereas protein levels of the positive regulator DWARF53 (D53) are decreased. Furthermore, high concentrations of sucrose can rescue the tiller bud growth defect of the rcn22 mutant. On the other hand, TB1 directly binds to the RCN22 promoter and downregulates its expression. The tb1/rcn22 double mutant shows a tillering phenotype similar to that of rcn22. Our results suggest that the TB1-RCN22-RbcL module plays a vital role in rice tiller bud elongation by affecting sugar levels.
作为一个重要的产量构成要素，水稻分蘖数控制着穗数并决定籽粒产量。此前尚未有关于叶绿体五肽重复序列（PPR）蛋白对水稻分蘖数调控的报道。在此，我们报道了水稻少茎数22（rcn22）突变体，该突变体由于分蘖芽伸长受抑制而产生的分蘖很少。图位克隆显示，RCN22编码一种定位于叶绿体的P型PPR蛋白。我们发现RCN22特异性结合RbcL mRNA（编码核酮糖-1,5-二磷酸羧化酶/加氧酶的大亚基）的5' UTR并增强其稳定性。rcn22中RbcL mRNA丰度降低导致光合速率降低和糖分水平下降。因此，DWARF3（D3）和玉米分枝素1（TB1）（编码分蘖芽伸长的负调控因子）的转录水平升高，而正调控因子矮化53（D53）的蛋白水平降低。此外，高浓度蔗糖可以挽救rcn22突变体的分蘖芽生长缺陷。另一方面，TB1直接结合RCN22启动子并下调其表达。tb1/rcn22双突变体表现出与rcn22相似的分蘖表型。我们的结果表明，TB1-RCN22-RbcL模块通过影响糖分水平在水稻分蘖芽伸长中起关键作用。
