Mapping And Verification Of QTL For Grain Protein Content In Brown Rice(Oryza Sativa L.)

Grain protein content?GPC?in rice is a key factor determining nutritional and eating and cooking quality.Clarifying the genetic mechanism underlying GPC is important for improving rice grain qualities.In this study,combining molecular genetic map and two-year data of GPC,quantitative trait locus?QTL?controlling GPC was identified using the Huanghuazhan/Jizi1560?HHZ/JZ1560?recombinant inbred line?RIL?population.Then one stably inherited QTL named as qGPC1-1 was validated using three residual heterozygotes?RH?derived F₂ populations and three advanced backcross BC₃F₃ populations.The main results are summarized as the following:1.GPC of brown rice flour for the 280 RILs and the parents were measured by kjeldahl nitrogen determination?KND?and near infrared reflectance spectroscopy?NIRS?method.Significant positive correlations between the GPC values determined by the two methods or in different years were observed.However,correlation coefficients for GPC measured by KND and NIRS methods as 0.966 in 2016 and0.983 in 2017 were much higher than that of GPC measured with the same method in different years as0.638 for NIRS and 0.631 for KND.This suggested that GPC measured by NIRS was quite consistent with that by the KND method,and GPC was easily influenced by environmental conditions.The GPC of RILs showed a continuous segregation and significant transgressive segregation.Using the high-density genetic map containing 18,194 SNP markers,14 QTLs were detected on the whole genome except for chromosomes 6,9 and 12 with each QTL explaining 0.81%–18.59%of the phenotypic variations.Seven of the 14 QTLs were repeatedly identified across two years.QTL analysis was also performed using a gel-based low-density genetic map containing 208 SSR and InDel markers and a total of fourteen QTLs were detected in the same HHZ/JZ1560 RIL population,but only three QTLs were repeatedly mapped at the same regions for two years.The stably expressed qGPC1-1 was detected on the short arm of chromosome 1 across two years and accounted for 9.14%to 11.85%of the phenotypic variations.The allele from JZ1560 at this locus increased GPC with a relatively large additive effect.The results provided a basis for verification and fine mapping of qGPC1-1.2.Verification of qGPC1-1 was performed.Three RH-derived F₂ populations consisting 180,137and 115 individuals,respectively,named as WB01,WB02 and WB03,were developed from three selfed F₈ RH plants which were selected from one RIL line with the heterozygous genotype covering the target marker interval JD1006-JD1007.QTL analysis was performed after additional InDel markers were developed,and then qGPC1-1 was identified in WB01 and WB02 populations,with the JZ1560 allele increasing GPC,but no QTL for the GPC was detected in the WB03 population.Combined the QTL analysis results,qGPC1-1 was validated and delimited to the interval between JD1006 and JD1075??862 kb?.Furthermore,we constructed three BC₃F₃ populations onsisting 144 individuals,respectively,named as LW01,LW02 and LW03,with HHZ as the recurrent parent to validate the effect of qGPC1-1in different genetic background,and then qGPC1-1 was detected in LW01 and LW02 populations,but no QTL for the GPC was identified in the LW03 population.Combined the QTL analysis results of three BC₃F₃ populations,qGPC1-1 was validated again and delimited to the interval JD1006-JD1071??597kb?.Our results are helpful in dissecting the genetic basis underlying GPC and improving rice grain qualities through molecular assisted selection.The stably inherited qGPC1-1 located on the short arm of chromosome 1 was validated and delimited in a relatively small region,which lay a foundation for fine mapping and cloning of this QTL.