Fine Mapping of , a Quantitative Trait Locus for Flag Leaf Nitrogen Content, Stomatal Conductance and Photosynthesis in Rice.

Increasing the rate of leaf photosynthesis is one important approach for increasing grain yield in rice (). Exploiting the natural variation in CO assimilation rate () between rice cultivars using quantitative genetics is one promising means to identify genes contributing to higher photosynthesis. In this study, we determined precise location of () by crossing a high-yielding cultivar with a Japanese commercial cultivar. Fine mapping suggested that encodes a putative Heme Activator Protein 3 (OsHAP3) subunit of a CCAAT-box-binding transcription factor called OsHAP3H. Sequencing analysis revealed that the allele of has a 1-bp deletion at 322 bp from the start codon, resulting in a truncated protein of 125 amino acids. In addition, is identical to , which was reported to control rice flowering date. The increase of is largely due to an increase of RuBP regeneration rate via increased leaf nitrogen content, and partially explained by reduced stomatal limitation via increased stomatal conductance relative to . This allele also increases hydraulic conductivity, which would promote higher stomatal conductance. This indicates that affects multiple physiological aspects relating to photosynthesis. The detailed analysis of molecular functions of would help to understand the association between photosynthesis and flowering and demonstrate specific genetic mechanisms that can be exploited to improve photosynthesis in rice and potentially other crops.