Poster: Oxidative stress

Abs # 78: Distinctions in flooding-induced activation of Rop GTPase signaling in submergence tolerant and intolerant genotypes of rice.

Presenter:	Fukao, Takeshi , fukao@ucr.edu
Authors	Fukao, Takeshi  (A)   Bailey-Serres, Julia  (A)
Affiliations:	(A): The Center for Plant Cell Biology, Department of Botany and Plant Sciences, University of California, Riverside

Promotion of anaerobic respiration is a common response to oxygen deprivation in many plants. However, prolonged induction of anaerobic metabolism may result in carbohydrate starvation. Rho-like GTPase of plants (Rop) is a monomeric G-protein that regulates various physiological and morphological traits including flooding tolerance. In Arabidopsis, oxygen deprivation activates Rop signaling which promotes hydrogen peroxide production. This signaling is controlled by negative feedback induction of a Rop GTPase activating protein (RopGAP). Thus, paradoxically oxidative stress can contribute to intolerance to oxygen deprivation. We investigated the role of Rop signaling in the low-oxygen stress response in japonica rice (M202). Rop-GTP levels increased transiently in roots during 48h of oxygen deficiency. Of the seven known RopGAP genes only one, located on chromosome 1 (RopGAP1), displayed increased transcript accumulation during the stress. Consistent with findings in Arabidopsis, alcohol dehydrogenase activity and hydrogen peroxide levels increased under oxygen deprivation, but these responses were inhibited by diphenylene iodonium (DPI), an inhibitor of flavin-binding oxidases including NAD(P)H oxidases. Examination of Rop-signaling in submergence tolerant near isogenic line (Sub1; M202 background) and intolerant inbred line (sub1; M202) revealed distinctions in the transient increase in Rop-GTP and transcripts encoding proteins involved in anaerobic metabolism. The accumulation of RopGAP1 was also genotype-specific and correlated with the transient elevation of Rop-GTP in each line. These results indicate that distinctions in the timing and level of Rop signaling underlie genetic variation in submergence tolerance in rice. Funded by USDA-NRI (2002-35100-13359).