Abstract
Grain weight is a major determinant of wheat (Triticum aestivum L.) yield and is controlled by quantitative trait loci (QTLs) derived from natural variations. Here, we report the cloning of a major yield QTL in bread wheat that functions in the chlorophyll biosynthesis pathway. We found that the natural variation of CHELATASE SUBUNIT I-A (CHLI-A), encoding a magnesium chelatase subunit, enhances chlorophyll content and photosynthesis rate, leading to increased leaf area and grain weight. Increasing CHLI-A expression increases grain weight, indicating that photosynthesis is a limiting factor of wheat yield potential. The CHLI-A gene is absent in a portion of elite varieties, suggesting the potential of using this gene to improve grain yield in wheat.