| The application of semi-dwarf genes such as sdl and rhtl in rice and wheat has activated the first"green revolution" in the 60s in the last century.However such semi-dwarf gene that can efficiently reduce plant stature and has few negative yield traits has not been yet identified in maize.In this study,the short and tall inbred lines 52220 and Mo18W were crossed to construct F2 and F3:4 populations for the identification of such favor alleles of plant height in maize.The main results are as following:1?QTL mapping in the F2 population revealed one major QTL for plant height on maize chromosome 1 in the location from 80cM to 110cM,which could account for 26%of the total phenotypic variations.This major QTL of plant height was finally delimited in the segment between the markers V2 and V4,which contained 354kb sequences on maize chromosome 1.2.Annotation analysis revealed about 8 genes located in this 354kb fragment,which contained the Br2 gene encoding P-glycoprotein controlling the polar transport of auxin,and belonging to Protein family MDR/PGP.Sequence analysis of Br2 gene was performed.The Br2 gene contained a 6,655-bp fragment comprising 5exons and 4 introns in the tall parent line Mo18W.While the br2 gene in the short parent line 52220 contained a 241bp-deletion in the fifth exon from 6376bp to 6617bp and led to the loss of a part of the second P-loop NTPase domain in translation.However,the 241bp-deletion was only detected in 52220 in the scanning of 311 maize accessions including 76 landraces and 235 inbred lines,signified the deletion had not yet been used in maize breeding.Therefore,this 241 bp-deletion of br2 was designated as super allele of br22(subr2).3?To estimate the potential to apply maize br2 gene with 241 bp-deletion in maize breeding,we performed large phenotypic measurements for four sets of NIL-like lines from F4 population,each of which contained normal Br2 and unnormal br2 with 241 bp-deletion.Plant height,ear height,plant height without tassel and the relative ear height(ear height/plant height)were fairly significantly decreased in the br2 lines,compared to the Br2 lines in these four families.While leaf length,leaf angle,leaf number above ear and tassel length showed smaller values in br2 lines from all four families.No significantly reduced trait was present in tassel primary branch number,husk leaf number,ear length,ear row number,kernel number per row,ear diameter in br2 lines,compared with Br2 lines from all four families.4?To ask how Br2 gene controls plant height,comparative RNA-seq analysis between maize and sorghum was then conducted from the stalks of both NIL-like plants with normal Br2 and unnormal br2 gene at the early and middle jointing stages.Finally we found the number of differentially co-expressed gene was 42 in the early stage and this number increased to 99 in the middle stage of jointing between maize and sorghum.The results indicated that Br2 gene may positively control the cellulose synthesis gene Csldl and negatively regulate the gene D3 and BAK1 involved in biosynthesis of GA and BR respectively and negatively regulate the gene Actin?controlled the auxin efflux regulator as well.All above results revealed that a rare allele of Br2 gene in the short inbred line 52220 named subr2 was involved in many phytohormone metabolism pathways during plant height development and the rare allele subr2 has a good potential to modify plant architecture including plant height in maize. |
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