Auxin up-regulates sulfur deficiency-responsive gene expressions

Abstract

Under sulfur deficiency, plants induce expressions of a set of genes (-S_up genes) to enhance sulfate uptake, distribution and assimilation. To identify a factor(s) regulating -S_up gene expression, we isolated nbm2 mutants using a chimeric sulfur deficiency-responsive promoter containing βSR fragment (Ohkama et al., 2002) as an indicator of -S_up gene expression. In nbm2-1 mutant, expression of -S_up genes were induced under normal culture condition. nbm2 mutants have mutations in the BIG gene and this lesion is the cause of up-regulation of -S_up genes. Auxin transport is inhibited in reported big mutants. βSR promoter activity was induced by treatment with polar auxin transport inhibitor. This effect was prominent in nbm2-1. Indole-3-acetic acid (IAA) content in leaves of nbm2-1 was about 10% higher than wild-type. IAA application induced -S_up gene expressions. Possible roles of IAA in -S_up gene expressions will be discussed.