| The grain numbers per spike is one of the important factors determining yield,The development of young spikes of wheat is very important to the number of grains per spike.It is important to excavate the genes involved in spike development.A new recessive natural mutant,Sterile and malformed spike 1(sms1),was characterized with reduced spikelet number and dysfunction in both male and female.The sms1 was located between SSR178 and SSR231,with a genetic distance of 0.22 c M and a physical distance of about 3.4 Mb.In this study,The agronomic traits of mutants and wild type were compared by means of near-isogenic lines,and the genes were further fine mapping.We further analyzed the sequence and gene expression of candidate genes,and constructed wheat genetic transformation vector.Combining the above work with transcriptome analysis,we preliminarily understand the genetic mechanism of sms1,which lays a foundation for elucidating the regulatory mechanism of sms1.The main results of this study are as follows:1.In order to evaluate the effect of sms1 on important agronomic traits,the main agronomic traits of wild type and mutant in two near-isogenic lines were compared.There were significant differences between mutant and wild type in grain numbers per spike,spikelet number and spikelet density.Compared with wild type,the mutants were mostly not fruitful,the spikelets per spike decreased by 4.13-6.59,and the spikelet density decreased by 0.27-0.61/cm.2.The transcriptome analysis showed that the differentially expressed genes between wild type and mutant were mainly at down-regulated level.GO enrichment analysis showed that the differentially expressed genes were highly enriched in“translation”,“peptide biosynthesis”,“peptide metabolism”,“ribosome” and “enzyme activity”.Differential gene KEGG analysis showed that the most abundant genes were involved in metabolism,biosynthesis,hormones,RNA biological processes.These results suggest that the changes of spike development in mutant may be due to the changes of basic metabolic components in mutant.Pathway enrichment analysis provides important information for predicting the function of candidate genes and explaining the mechanism of candidate genes.3.The sms1 was fine-mapped to a 0.048 c M genetic interval with a ~860 Kb physical interval on chromosome 6B.In the ~ 860 Kb sms1 physical regions defined by SSR178 and SSR277,only three genes,Traes CS6B01G354700,Traes CS6B01G354800 and Traes CS6B01G354900,were annotated Traes CS6B01G354700 encodes a protein homolog with Arabidopsis X-ray induced 1(XRI1),required for male and female meiosis.Traes CS6B01G354800 is a nuclear RNAi defective-2(NRDE-2)homolog necessary for RNA interference,and Traes CS6B01G354900 encodes a protein belonging to Homeobox-leucine zipper family.4.Three candidate genes were sequenced and analyzed.A G/A SNP was found in the promoter region of Traes CS6B01G354700.A G/A SNP and a fifth intron base were found in the promoter region of Traes CS6B01G354900,but no polymorphism was detected in Traes CS6B01G354800.Expression analysis of the 3 candidate genes in sms1 region show that Traes CS6B01G354700 and Traes CS6B01G354900 have low expression levels in other tissues and high expression in spikes.During spikelet development,the expression level of Traes CS6B01G354700 peaked at AM and then decreased gradually.The expression of Traes CS6B01G354900 decreased at the beginning but increased at FM stage.The expression of Traes CS6B01G354800 had no obvious tissue specificity and during spikelet development.the amount of expression is very low.The expression levels of three candidate genes in mutants were lower than those in wild-type.The expression of Traes CS6B01G354700 and Traes CS6B01G354900 in the mutant was significantly lower than that in the wild type,but the expression of Traes CS6B01G354800 in the mutant was not significantly decreased.Traes CS6B01G354700 showed a significant and strong correlation with the trait of spikelet number per spike,floret number per spike and seed number per spike,while other two genes showed no significant correlations with any trait.5.At present,wheat transgene vectors have been constructed for three candidate genes.Transgenic plants are growing.The next step is to further study the mechanism of the target genes. |
