Abstract
Little is known about the genetic basis of leaf and canopy photosynthesis. Here we aimed to detect novel quantitative trait loci (QTL) controlling photosynthesis by increasing leaf nitrogen content (LNC) per leaf area and analysed its effect on leaf and canopy photosynthesis. To identify QTL that increase photosynthetic rate in leaves, we screened chromosome segment substitution lines (CSSLs) of Oryza sativa ssp. japonica cultivar Koshihikari and O. sativa ssp. indica cultivar Nona Bokra using LNC per leaf area as the phenotype indicator. Locus leaf nitrogen content on chromosome four (qLNC4) is associated with increased LNC and photosynthetic rate per leaf area. Moreover, a non-synonymous amino acid substitution was identified in the NARROW LEAF 1 (NAL1) gene located in the qLNC4 region. This NAL1 allele increases LNC and photosynthetic rate per leaf area in flag leaves but does not increase whole-leaf photosynthesis. This NAL1 allele also increases light capture and whole-leaf nitrogen content of the lower leaves and is associated with slower senescence in flag leaves. These results suggest that this NAL1 allele does not increase whole-leaf photosynthesis but plays a role in regulating spatial and temporal trade-offs among traits at the whole-plant level.
Highlights
Improving photosynthesis is important to increase biomass and crop yield in plant breeding
Log of odds ratio (LOD) scores were calculated with a threshold of 2.198 (α = 0.01), and the qLNC4 locus was restricted to a 286-kb region between markers S1704 and S292-1 (Fig. 2)
We identified the Quantitative trait loci (QTL) that increased leaf nitrogen content (LNC) in the indica cultivar Nona Bokra allele (Fig. 1 and Supplementary Fig. S1)
Summary
Improving photosynthesis is important to increase biomass and crop yield in plant breeding. The uppermost, fully expanded leaf displays the maximum rate of photosynthesis in a plant, a target for increasing yield potential through increasing photosynthetic rate per leaf area. To improve whole-plant photosynthesis, it is important to increase both the Pn in uppermost leaves and canopy photosynthesis. Takai et al.[19] reported that a partial loss-of-function by amino acid substitution in the NARROW LEAF 1 (NAL1) gene, or a decreased NAL1 protein level due to the indica Takanari allele, contributed to increase LNC, leaf Rubisco contents, and Pn. NAL1 encodes a protein that might be involved in polar auxin transport and is known to control vein patterning and leaf blade morphology[20]. In order to improve photosynthetic productivity, canopy photosynthesis needs to be taken into consideration
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