QTL Mapping Of Tillering In Foxtail Millet Under Different Planting Densities

As the dominant coarse cereals in Shanxi province,foxtail millet has the advantages of short growth time,drought tolerance,storage tolerance,be barren,C₄photosynthetic characteristic,adaptability wide and so on.Tillering is one of the important agricultural traits t,which directly influences plant architecture and yield,however,the regulatory mechanism for tilleting is largely unknown in foxtail millet.In this study,the RIL population containing 122 lines was constructed from the cross Heizhigu（tillering）and Changnong 35（non-tillering）,a high-density genetic map was constructed by resequencing technology,and the tiller number QTLs were located in combination with the tiller number phenotype under three planting density conditions in two years,and molecular markers closely linked to tiller number were further developed.At the same time,the remaining heterozygous individual of the dominant QTL q TN5-6 were selected by molecular marker combined with and the phenotype,which laid the foundation for fine localization in the later period,and the candidate genes of q TN5-6 were predicted and analyzed.The results are shown as follows:（1）A high density genetic map containing 3795 Bin markers was constructed.The average sequencing depth of female,male and RIL populations were 39.28×,33.36×and 12.65×,respectively,and the coverage ratio reached 88.19%,92.25%and 56.17%,respectively.A total of 7,693,246 SNPs and 1,875,887 In Del were detected in parents and RIL population..A high-density genetic map containing72,241 SNP and 3,795 Bin and spanning 3164.7 c M was constructed,and the average genetic distance between adjacent SNP was 0.88 c M.（2）In the six environmental conditions,a total of 11 QTL for tiller number related were deteted,and these QTL,distributed on Chr.1,2,4,5 and 9,respectively,the largest number were located on Chr.5.the genetic effects of these QTLs were all derived from the female parent,and q TN5-6 was co-located in four environments,with the PVE ranges from 8.87 to 19.5%.（3）The tightest linked marker of the major effect QTL q TN5-6 was developed.Five polymorphic markers,MRITN1,MRITN2,MRITN4,MRITN5 and MRITN17were developed in the overlap interval（Chr.5 410,436,30-41,653,372bp）of q TN5-6,correlation analysis showed that the markers were significantly correlated with tillering phenotypes,and MRITN1 was the most closely linked marker.（4）The remaining heterozygote single lines that could be used for fine localization of q TN5-6 were screened.Use the developed molecular marker,the remaining heterozygote single plants whose q TN5-6 location interval was heterozygote were screened in RIL population,the results showed that mainly concentrated in RIL3-10,RIL3-154 and RIL3-221,which laid an important foundation for the fine mapping and candidate gene cloning of q TN5-6.（5）Candidate genes for q TN5-6 were preliminarily predicted.The physical interval size of q TN5-6 was 610 kb,containing 91 genes.According to gene annotation and resequencing data,Seita.5G376000,encoded an F-box protein,was predicted as a key candidate gene.Previous studies have shown that F-box protein involved in the regulation of tiller and branch formation in Arabidopsis thaliana and rice,and it is speculated that this gene may be related to tillering traits of foxtail millet,as one of the important candidate genes for q TN5-6.By comparing Seita.5g376000sequence in the parents,we found that Changnong 35 had a 12bp insertion in exon 1.The FPKM value of MDSi database showed that Seita.5G376000 was the highest expression in immature spikelets S2,but the expression level was low in other tissues and organs.There are several cis-acting elements involved in hormone regulation and meristem correlation in the promoter region of this gene.QRT-PCR exhibited expression of this gene was up-regulated after GR24 hormone treatment,but down-regulated after GA3,ABA,IAA,Me JA hormone and 4℃,PEG abiotic stress.