Han Yun

The growth of young roots is crucial for the development and yield of rice. However, the molecular mechanisms underlying young rice root development remain unclear. Our research indicates that the rice B-type cytokinin response regulator factor ORR3 negatively regulates the development of young rice roots. ORR3 is highly expressed in the root meristematic zone of young rice roots. In transgenic lines overexpressing ORR3, the lengths of primary roots and adventitious roots, as well as the corresponding root meristematic zone lengths, are significantly reduced. This is due to a decrease in both the number and size of longitudinal cells in the root meristematic zone. On the one hand, ORR3 can inhibit root apical cell division and reduce the number of longitudinal cells in the root meristematic zone by affecting the auxin synthesis and transport pathways. On the other hand, ORR3 may directly activate the transcription of cell wall metabolism-related genes, thereby restricting the size of cells in the root meristematic zone. In summary, ORR3 negatively regulates rice young root growth by responding to cytokinin signals to influence auxin signal transduction and cell wall metabolism pathways, thereby negatively regulating the number and size of cells in the root meristematic zone.

Analysis of growth and yield characteristics of rice with different yield levels is very important for the breeding of high-yield rice cultivators. To investigate the yield components’ variation, morphological characteristics of the panicles, leaves, and stems of rice varieties under different yield levels, a two-year field experiment was conducted in Chongqing China. The 20 mid-season Indica hybrid rice varieties were classified into three groups based on yield, comprising high-yield group (HG), mid-yield group (MG), and low-yield group (LG). The main reason for the superior yield of HG is that the varieties of this group had a significantly higher number of effective panicles per unit area than the MG and LG. In plant type factors, the leaf type factors were the most important reason causing yield difference of HG, MG, and LG. The average leaf roll index, average leaf length to width ratio, average leaf base angle, average leaf droop angle, and average leaf pillow distance of the upper three leaves were significantly or significantly negatively correlated with the yield, while the average leaf width, average leaf area, and the average distance of leaf edge were significantly or significantly positively correlated with yield, and the leaf droop angle was the most important plant type factor affecting the yield. Based on these results, we further quantified the plant type factors of HG and constructed an ideal plant type model for high-yield hybrid mid-season rice. Theoretical and practical basis could be provided for breeding mid-season Indica hybrid rice with super-high yield in the future to ensure food security.