| Mung bean is a traditional food legume in China,it plays important roles both in agriculture system adjustment and peoples' diets.Mung bean is a major resource of plant protein for poor people too.However,owing to the limited planting area and production,the genetic study on mungbean has been lagged far from those main crops,such as lack of polypmorphic markers and low-density linkage maps,which is a disadvantage for further genetic study.In the present study,we constructed a high SNP map based on a RIL population using genome-resequencing techonology and applied it onto QTL analysis of agronomic traits.The main results are are as follows:1.High-density genetic linkage mapA total of 564449 SNPs was identified between P1 and P2,and 1946 bin markers consisting of 21508 SNPs were finally located onto 11 linkage groups(LGs),and there was a good agreement between the LG and mungbea nchromosomes.The total length of the genetic map was 1060.17 cM with the average distance between adjacent markers at 0.54 cM.The ranks of the length of each LG was LG 9(168.03 cM)> LG 6(127.99 cM)> LG 1(114.27 cM)> LG 5(113.37 cM)> LG 8(112.09 cM)> LG 7(95.76 cM)> LG 10(87.85 cM)> LG 11(85.60 cM)> LG 2(71.90 cM)> LG 3(44.55 cM)> LG 4(38.76 cM).The average genetic distance of each LG was: LG 9(1.02 cM)> LG 11(0.74 cM)> LG 10(0.73 cM)> LG 6(0.56 cM)> LG 1(0.51 cM)> LG 8(0.5 cM)> LG 7(0.48 cM)> LG 3(0.45 cM)> LG 5(0.44 cM)> LG 4(0.4 cM)> LG 2(0.35 cM).There were 18 gaps on the map,distributing in four LG s,namely LG 9(7),LG 1(4),LG 5(4),LG 7(3).The largest gap(19.91 cM)was on LG 9.2.Identification of QTL for the agronomic traitsQTL analysis was performed for 16 agronomic traits,including lobed leaflet,indented leaflet,plant height,number of branch,pod length,pod width,seeds number per pod,seed coat color,seed coat luster,seed distribution density,initial flowering stage,leaf chlorophyll content,100-seed weight,young stem color,pollen viability and seed diameter.A total of 49 QTLs were detected in all 15 traits except for pollen viability,some QTLs are located between the same two markers.The distribution of these QTL mapping intervals on linkage groups was: LG 1(2),LG 2(3),LG 3(12),LG 4(3),LG 5(8),LG 6(3),LG 7(4),LG 10(12),LG 11(2).The number of QTLs(LOD > 3)detected for each trait:the initial flowering stage(7)> seed coat color(6)> lobed leaf Q(5)> lobed leaf R(4)=pod width(4)= seed distribution density(4)> leaf chlorophyll content(3)= pod length(3)= 100-seed weight(3)> plant height(2)= number of seeds per pod(2)= seed coat luster(2)> indent leaf(1)= number of branch(1)= seed diameter(1)= young stem color(1).3.The candidate gene and SNP analysis of leaf shapeWe further investigated the QTL and candidate gene related with leaf shapes in the present study.The indent leaflet was located between Block7460 and Block7463 on LG 10.Gene annotation showed that there were 35 protein-coding genes in the region.Further analysis showed that there were 7 SNPs in the gene,and only one non-synonymous SNP was in protein coding region of the gene,LOC106775793.Indent leaflets were caused by a single point mutation in the gene LOC106775793,which encoded TCP2.The mutation site was at position 16777103(G?A)on chromosome 10,and the codon was changed from encoding tryptophan to a terminator,which hindered the expression of TCP2 and made leaflet being indent.A common QTL was detected both in 2018 and 2019 with two different methods,and this QTL located between Block18747 and Block18748.There were 10 protein-coding genes as annotated,of which 7 genes have non-synonymous mutation SNP sites.LOC106757416 was most likely related to lobed leaves.Because this gene encodes a glycosyltransferase.It has been reported that overexpression of the glycosyltransferase gene in tobacco resulted in irregular leaf vein arrangement. |
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