NtGRAS1, a novel stress-induced member of the GRAS family in tobacco, localizes to the nucleus

Abstract

We report the isolation and initial characterization of a new member of the GRAS gene family from tobacco, NtGRAS1. Analysis of the predicted amino acid sequence shows that NtGRAS1 shares the highly conserved carboxy-terminal motifs common to all members of the GRAS family. NtGRAS1 expression was strongly induced in tobacco (BY-2) suspension cells by antimycin A, H(2)O(2), salicylic acid, and L-cysteine which were all found to raise intracellular reactive oxygen levels. An increase in NtGRAS1 expression was also triggered by treating cells with the nitric oxide donor sodium nitroprusside. By employing inhibitors of protein kinase and phosphatase action, we show that reversible phosphorylation is required for the stress-induced induction of NtGRAS1 and that reactive oxygen as well as NO-dependent signaling pathways probably share key intracellular components. Interestingly, in soil-grown plants, high constitutive expression of NtGRAS1 was found only in roots while expression was strongly induced in leaf tissue upon antimycin A treatment or following Pseudomonas syringae infection. Many members of the GRAS family are implicated in regulating transcription and this function for NtGRAS1 is supported by our finding that an NtGRAS1-GFP fusion protein localizes to the nucleus of onion epidermal cells. Our data suggest that NtGRAS1 may represent an important transcriptional regulator involved in the plant stress response.