Phytochrome-mediated differential gene expression of plant Ran/TC4 small G-proteins

Ran/TC4 is the only known member of the family of small GTP-binding proteins primarily localized inside the nucleus. We cloned a pea Ran gene (PsRan1) and characterized its expression in tissues, and under different light sources. PsRan1 is a member of a highly homologous multigene family, and it encodes a protein containing plant-specific amino acids in its sequence. It is ubiquitously expressed in pea tissues with high expression in radicles. The amount of total mRNA transcripts representing multiple Ran family members increased in response to very low-fluence R, while the amount of mRNA transcript encoding PsRan1 specifically was not affected by various light treatments. In addition, Ran genes in Arabidopsis were also differentially expressed in various mutants defective in phytochromes or the light-responding HY5 protein, such as phyA, phyB, and hy5. AtRan1 and AtRan3 gene expression was significantly reduced in the phyA mutant background compared to that in Ler-0 wild type plants. AtRan1 expression was also decreased in the phyB background. In contrast, the expression of AtRan2 did not vary in the hy5 and phytochrome mutant backgrounds examined. Interestingly, expression of AtRan1 was significantly reduced in hy5 plants, while AtRan3 expression was increased in the same plants. From these results, we conclude that Ran gene expression is differentially regulated by various light sources and phytochrome-mediated signaling pathways.