Identification of QTL for kernel number-related traits in a rice chromosome segment substitution line and fine mapping of qSP1

A chromosome segment substitution line (CSSL) is a powerful tool for combining quantitative trait locus (QTL) mapping with the pyramiding of desirable alleles. The rice CSSL Z1364 with increased kernel number was identified in a BC3F8 population derived from a cross of Nipponbare as the recipient with Xihui 18 as the donor parent. Z1364 carried three substitution segments distributed on chromosomes 1, 6, and 8. The mean substitution length was 1.19 Mb. Of 17 QTL identified on the substitution segments, qSP1 for spikelets per panicle, qSSD1 for seed-set density, and qNSB1 for number of secondary branches explained respectively 57.34%, 87.7%, and 49.44% of the corresponding phenotypic variance and were all linked to RM6777. Chi-square analysis showed that the increased kernel number in Z1364 was inherited recessively by a single gene. By fine mapping, qSP1 was delimited to a 50-kb region on the short arm of chromosome 1. Based on DNA sequence, a previously uncharacterized rice homolog of Arabidopsis thaliana AT4G32551 was identified as a candidate gene for qSP1 in which mutation increases the number of spikelets and kernels in Z1364. qSP1 was expressed in all tissues, but particularly in 1-cm panicles. The expression levels of OsMADS22, GN1A, and DST were upregulated and those of LAX2, GNP1, and GHD7 were downregulated in Nipponbare. These results provide a foundation for functional research on qSP1.

Morphological and physiological analysis of narrow and striped leaf 1(nsl1) mutant of rice(Oryza sativa L.) and the gene mapping

The shape and color of rice leaves are important agronomic traits that directly influence the proportion of sunlight energy utilization and ultimately affect the yield and quality.A new mutant exhibiting stable inheritance was identified as derived from ethyl methane sulfonate(EMS)-treated restorer Jinhui 10,tentatively named as narrow and striped leaf 1(nsl1).The nsl1 displayed pale white leaves at the seeding stage and then white striped leaves in parallel to the main vein at the jointing stage.Meanwhile,its leaf blades are significantly narrower than the control group of Jinhui 10.The chloroplast structures of cells in the white striped area of the nsl1 mutant break down,and the photosynthetic pigments are significantly lower than that of the wild type.Moreover,fluorescence parameters,such as F0,F v/F m,U psII,qp,and ETR,in the nsl1 mutant are significantly lower than those of the wild type,and the photosynthetic efficiency is also significantly decreased.These changes in leaf color and shape,together with physiological changes in the nsl1,result in smaller plant height and a decrease in the most important agronomic traits,such as the number of grains per panicle,grain weight,etc.Genetic analysis shows that the narrow and striped traits of the nsl1 mutant are controlled by a single recessive nuclear gene,which is located between InDel 16and InDel 12 in chromosome 3.The physical distance is204 kb.So far,no similar genes of such leaf color and shape in this area have been reported.This study has laid a solid foundation for the gene cloning and function analysis of NSL1.