The Expression And Functional Study Of AtSPX3 Gene In Arabidopsis Thaliana

The proteins with conserved SPX domain in yeast (Saccharomyces cerevisiae) are involved in phosphorus signal system, including phosphate level sensor PHO81. The function of most genes in eukaryotic organisms with SPX domain is still unknown. Therefore, Investigation of SPX domain genes will provide an insight into the phosphate signaling networks.One gene with SPX domain in Arabidopsis, At2g45130, named as AtSPX3, was investigated in this study. The expression patterns of AtSPX3 revealed by RT-PCR showed that: AtSPX3 was strongly induced after Pi-starvation for 5 days in both roots and shoots. This induction was rapidly reduced by supplement of Pi, indicating that AtSPX3 is specially responsive to Pi-signaling. The expression of AtSPX3 gene was induced by Pi-starvation. Analysis of the activity of the promoter of AtSPX3 gene using promoter-β-glucuronidase fusion revealed a predominant expression in the vascular tissues of roots, leaves, and also in the mature microspore. The RT-PCR results are consistent with that revealed by GUS expression. AtSPX3-GFP protein was localized to chloroplast and proplastid. Under Pi-starvation, GUS expression was obviously depressed in AtSPX3 promotor-driven GUS transgenic phr1 mutant lines. Moreover, RT-PCR results revealed that the expression of AtSPX3 in phrl was reduced, suggesting PHR1 may function at the upstream of AtSPX3. Transgenic lines with RNAi of AtSPX3 showed supersensitive to Pi-starvation compared with Col. The expression of several Pi-starvation responsive marker genes in RNAi transgenic lines showed different patterns in shoots and roots. Our results indicate that AtSPX3 may function at the downstream of PHR1, and play an important and positive role in plant adaptation to Pi-starvation.