Light regulation of nitrate reductase gene expression in maize involves a G-protein

Abstract

This paper reports three lines of evidence to demonstrate the presence of heterotrimeric G-proteins in maize and their involvement in the regulation of nitrate reductase gene expression by light: (1) Southern blot analysis of maize genomic DNA using a human Ha-ras cDNA probe revealed specific bands indicating the presence of G-protein (α subunit) gene(s) in maize. Northern blot analysis of maize total RNA using the same probe revealed that the putative Ga gene(s) is transcriptionally active. (2) Western blots containing purified plasma membrane proteins from maize leaves showed specific binding of γ[³⁵S]-labeled GTP in a red light-dependent manner, indicating the involvement of G-proteins in mediating the light signal. The size of the putative Ga gene product (~45 kDa) indicates that it may be a heterotrimeric G-protein. (3) Cholera toxin mimicked the effect of red light to enhance the transcript levels of nitrate reductase (NR), indicating that G-proteins may mediate light regulation of NR gene expression.