Genome-wide identification and expression profiling analysis of the SPX gene family in Setaria italica

Abstract Background In plant adaptation to adversity, phosphorus is pivotal and exerts a beneficial influence on both yield and quality formation in foxtail millet. Proteins containing SPX domains are essential for the maintenance of phosphate ion (Pi) balance in plants. However, the mechanisms that control phosphorus deficiency in foxtail millet are not yet fully understood. Results Through genome-wide analysis, we identified 15 members of the millet SPX gene family, which were categorized into four subfamilies (SPX, SPX-MFS, SPX-EXS, and SPX-RING) according to their structural characteristics. The genes encoding proteins with SPX domains were found on six out of the 9 chromosomes. Enrichment for multiple biotic and abiotic stresses, as well as hormone responses, was observed in the promoter regions of SiSPXs. Analysis of transcriptome data (RNA-seq) revealed diverse expression patterns among 15 genes encoding SPX-domain-containing proteins. Under low phosphate (Pi) stress, specific members, such as SiSPX3, and SiSPX9, showed a pronounced response. Conclusions The SPX gene primarily regulates phosphorus homeostasis and transport in foxtail millet by binding to the signal molecule InsP8.This study enhanced the comprehension of the millet SPX gene family, thereby advancing future biological investigations of SiSPX genes in millet. Additionally, it offers a selection of potential candidate genes for functional research on phosphate ion (Pi) nutrition in millet.