QTL Analysis For Photosynthesis Related Traits In Rice (Oryza Sativa L.)

Photosynthetic traits especially nitrogen content(TNC), net photosynthetic rate(NPR),transpiration rate(TR) and intercellular CO₂ concentration(CI) in flag leaf are consideredimportant index related to the leaf photosynthetic ability. In our study, different populationswere put into quantitative trait loci (QTLs) analysis and genetic dissection forphotosynthetic traits. Meanwhile, a secondary F₂ populations, which derived from the crossbetween target CSSLs and genetic background parent were conducted for QTL mapping ofphotosynthetic traits. The main conclusions are as follows:1,In this study, a BIL(backcross inbred lines) population derived from a cross ofNipponbare/Kasalath//Nipponbare was employed to detect quantitative trait loci (QTLs)underlying the TNC, NPR and TR which were measured on the 7th day after heading in2005 and 2006, respectively. As a result, five QTLs (qTNC-1, qTNC-3a, qTNC-3b, qTNC-9and qTNC-12) controlling TNC were detected on chromosomes 1, 3, 9 and 12 with LODscores ranging from 2.07 to 19.07 and percentages of variance explained (PVE) from3.51% to 18.7%, respectively. Among the QTLs reported in this study, qTNC-3a, qTNC-9,qTNC-12 are newly detected. One QTL qNPR-6 controlling NPR was detected onchromosome 6, with LOD score of 3.06 and PVE of 4.73% and QTL for TR, namelyqTR-10, was detected with LOD score of 6.59 and PVE of 7.45%. Meanwhile, complicatedinteractions among the QTLs were detected, thus a corresponding population ofchromosome segment substitution lines (CSSLs) in Nipponbare genetic background wasused in 2006 to further dissect the effect of single QTL. It is noteworthy that the QTLscontrolling TNC namely qTNC-3a, qTNC-9 and qNPR-6 were detected repeatedly indifferent environments.2,In the present study, the total nitrogen content in flag leaf of AIS54 showed significantlyhigher than cultivar Asominori using IR24 chromosome segment substitution lines(CSSLs)in Asominori genetic background. The repeat results obtained in the following yearindicated that the IR24 segment on chromosome 7 of AIS54 may harboring QTL namelyqTNC-7 associated with high total nitrogen content in rice. Consequently, mapping fortarget QTL was conducted in 2005 based on the F₂ populations that derived from the cross of AIS54 and Asominori and 31 individuals with high and low nitrogen content selectedfrom F₂ population and corresponding F₃ population. A genetic linkage map wasconstructed and the existence of qTNC-7 was confirmed empolying the phenotypic valuesand SSR marker data of the selective 31 individuals by the composite interval mapping.Then, qTNC-7 was further mapped between RM3691 and RM21690 on chromosome 7 andshowed minor effect with LOD score of 3.2 and PVE of 4.0% using the 614 F2 plants andSSR markers. The results indicated that the QTLs interaction may existed between andbeyond the region of substitution segment on chromosome 7 and experimental errors mayalso influence the genetic effect of qTNC-7. These results provide an important case forQTL mapping for high nitrogen content in rice and should be useful for high photosyntheticefficiency MAS breeding in rice and map-based cloning of target QTLs, although the minoreffect of qTNC-7 make it impossible to further proceed the fine mapping of target QTL.