Dissection And Verification Of PTGW1-2,A QTL For Grain Weight And Size In Rice

Grain weight and size that are the key traits determining rice quality and yield,are mainly controlled by quantitative trait loci（QTL）.In our previous study,one QTL qTGW1-2 controlling grain length and weight was detected in the marker interval JD1009-JD1019 at the end of long arm of chromosome 1 using the recombinant inbred line（RIL）population constructed by indica-japonica rice cross Huanghuazhan/Jizi1560（HHZ/JZ1560）.Two types of populations derived from the same parents with highly homogeneous genetic background were developed.Among them,one type population was derived from the residual heterozygote（RH）in one RIL,including one sets of near isogenic line（NIL）and 12 NIL-F₂ populations in F₉/F₁₀/F₁₁;the other was developed from one individual in the BC₃F₂population that was a backcross inbred population with HHZ as the recurrent parent,including 2 sets of NILs and 13 NIL-F₂ populations in BC₃F₃/BC₃F₄/BC₃F₅.Based on the genetic analysis of these populations,qTGW1-2 was confirmed to regulate TGW,GL and GW,and was finally dissected into two minor QTLs.1.Verification and dissection of qTGW1-2Firstly,according to the primary mapping of qTGW1-2,three F₉ populations with sequential residual heterozygous regions covering JD1009-RM6840 were developed.The results of QTL analysis confirmed the genetic effects of qTGW1-2 for TGW,GL and GW.However,obvious difference of the additive effects in different populations with different segregating regions was detected,which suggested there might be at least two QTLs controlling grain weight and size in the target region of qTGW1-2.To confirm our conjecture,QTL analysis of seven F₁₀ populations confirmed that there were two QTLs controlling TGW,GL and GW in the target region,named as qTGW1-2a and qTGW1-2b,which were located in the marker intervals of JD1139-JD1062 and JD1052-JD1102,respectively.Secondly,three BC₃F₃ populations carrying different heterozygous regions covering JD1009-RM6840 were also developed.The genetic effects for TGW,GL and GW with the same direction with qTGW1-2 were observed in all three populations,but significant difference of additive effect indicated that there might be two or more QTLs regulating the three grain traits.According to the QTL analysis of four BC₃F₄ populations,qTGW1-2 was also dissected into qTGW1-2a and qTGW1-2b,which were located in JD1008-JD1127 and JD1023-RM6840,respectively.Finally,according to the mapping intervals of qTGW1-2a and qTGW1-2b,two F₁₂and six BC₃F₅populations with smaller segregating regions were developed.QTL analysis of 4 BC₃F₅ populations narrowed down qTGW1-2a into a 930.5-kb region,and QTL analysis of 2 F₁₂ and 2 BC₃F₅populations delimited qTGW1-2b into a 54.8-kb region flanked by JD1121 and JD1102.2.Validation of the genetic effects of qTGW1-2a and qTGW1-2bAccording to the target regions of qTGW1-2a and qTGW1-2b,homozygous non-recombinants in the F₁₁ and BC₃F₄ populations were selected to develop 3 sets of NILs in F_11:12 and BC₃F_4:5.Based on the phenotypic distribution and the results of QTL analysis,significant effects with the enhancing allele from JZ1560 of TGW,GL and GW were detected in both qTGW1-2a and qTGW1-2b region,and the genetic effects of this two QTLs were validated.In this study,based on the two types of genetic populations with highly homogeneous genetic background,qTGW1-2 was successfully validated to control TGW,GL and GW with the enhancing allele derived from JZ1560.Furthermore,qTGW1-2 was further dissected into two QTLs,qTGW1-2a and qTGW1-2b,which were respectively narrowed down to 930.5-kb and 54.8-kb regions.These results supplied important basis for further map-based cloning and molecular design breeding in rice,and enriched the understanding of minor QTLs.