Rice Plant Architecture: Molecular Basis and Application in Breeding

Shoot architecture in rice is determined by the number of leaves, stems, and panicles and by their size, shape, and position on the plant. These factors determine the effectiveness of light interception, the degree of competition between neighboring plants, and ultimately the number and mass of grains produced. Plant hormones including auxin, cytokinins, gibberellins, strigolactones, and brassinosteroids play key roles in regulating shoot development and architecture. The SEMI-DWARF1 (SD1) gene has contributed greatly to rice yields by redirecting resources from elongation growth to panicle development, providing resistance to lodging and increased harvest index. The mechanism of control of tillering by strigolactone signaling has been determined in recent years providing valuable information to help understand the timing and number of tillers produced. Genes that have been selected for increased yield have now been identified at the molecular level such as IDEAL PLANT ARCHITECTURE1 (IPA1), Grain size 3 (GS3), and GRAIN NUMBER, PLANT HEIGHT, AND HEADING DATE 7 (GHD7). The function of these genes in controlling gene transcription and shoot development is helping us to understand the molecular basis of plant architecture. The future offers great potential for the rational design of plant architecture using molecular breeding techniques.