AUTHOR=Adachi Shunsuke , Yoshikawa Kazuaki , Yamanouchi Utako , Tanabata Takanari , Sun Jian , Ookawa Taiichiro , Yamamoto Toshio , Sage Rowan F. , Hirasawa Tadashi , Yonemaru Junichi 

TITLE=Fine Mapping of Carbon Assimilation Rate 8, a Quantitative Trait Locus for Flag Leaf Nitrogen Content, Stomatal Conductance and Photosynthesis in Rice

JOURNAL=Frontiers in Plant Science

VOLUME=8

YEAR=2017

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2017.00060

DOI=10.3389/fpls.2017.00060

ISSN=1664-462X

ABSTRACT=<p>Increasing the rate of leaf photosynthesis is one important approach for increasing grain yield in rice (<italic>Oryza sativa</italic>). Exploiting the natural variation in CO<sub>2</sub> assimilation rate (<italic>A</italic>) 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 <italic>Carbon Assimilation Rate 8</italic> (<italic>CAR8</italic>) by crossing a high-yielding <italic>indica</italic> cultivar with a Japanese commercial cultivar. Fine mapping suggested that <italic>CAR8</italic> encodes a putative Heme Activator Protein 3 (OsHAP3) subunit of a CCAAT-box-binding transcription factor called OsHAP3H. Sequencing analysis revealed that the <italic>indica</italic> allele of <italic>CAR8</italic> has a 1-bp deletion at 322 bp from the start codon, resulting in a truncated protein of 125 amino acids. In addition, <italic>CAR8</italic> is identical to <italic>DTH8/Ghd8/LHD1</italic>, which was reported to control rice flowering date. The increase of <italic>A</italic> 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 <italic>A</italic>. This allele also increases hydraulic conductivity, which would promote higher stomatal conductance. This indicates that <italic>CAR8</italic> affects multiple physiological aspects relating to photosynthesis. The detailed analysis of molecular functions of <italic>CAR8</italic> 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.</p>