Auxin is one of the major endogenous hormones that regulate the spike morphology in crops.In order to explore the auxin pathway genes involving spike type in wheat,the line SY95-71 with spindle spike and line CH7034 with compacted spike were se-lected to detect the endogenous auxin content in their young spikes.The results showed that the tryptophan content in SY95-71,s young spikes was significantly higher than that in CH7034.RNA-seq results showed that four specific auxin-related GO items were enriched in SY95-71 young spikes within the high confidence interval(P＜0.01),and the relative expression levels of Tryptophan Decarboxylase genes(responsible for transforming tryptophan into tryptamine)and Auxin Response Factor genes(ARFs)in SY95-71 were significantly higher than those in CH7034.Further analysis of two highly expressed ARF genes(TraesCS7A02G475600 and TraesCS7A02G475700)in SY95-71 revealed that they were a pair of tandem repeat genes located on the long arm of chromosome 7A and named TaARF23-A1 and TaARF23-A2 based on the IDs of ARF family member in wheat,respectively.The qRT-PCR results confirmed that the relative expression levels of TaARF23-A1 and TaARF23-A2 in SY95-71 young spikes were significantly higher than those in CH7034.The sequencing results showed that the exon of TaARF23-A had two SNPs and one InDel site between SY95-71 and CH7034.A molecular marker was developed based on the InDel site and then used to associated with the spike pheno-types of the recombinant inbred lines population derived by the cross of SY95-71 and CH7034 in six field environments.The results showed that TaARF23-A was significant correlation with spikelet number(P＜0.0001),and its CH7034 allele increased by 1.67 spikelets compared with the SY95-71 allele.The results of this study provide the reference for the understanding of the development mechanism of spikelet and molecular marker for the improvement of ideal spike type in wheat.
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