Poster: Oxidative stress

Abs # 89: Investigating the interplay between Rop, MAPK and ethylene signaling in response to hypoxia in seedlings of Arabidopsis

Presenter:	Chang, Ruth , wandaster@yahoo.com
Authors	Chang, Ruth  (A) (B)  Branco-Price, Cristina  (A) (B)  Baxter-Burrell, Airica  (A) (B)  Bailey-Serres, Julia  (A) (B)
Affiliations:	(A): University of California, Riverside (B): Center for Plant Cell Biology and Department of Botany and Plant Sciences

Modulation of a RHO-like of plant (Rop) rheostat is essential for Arabidopsis thaliana seedling tolerance of oxygen deprivation (hypoxia). Hypoxia increases Rop-GTP levels, which lead to H₂O₂ production requiring a diphenyl iodonium (DPI)-sensitive flavoprotein(s). mRNAs encoding alcohol dehydrogenase (ADH) and a Rop GTPase activating protein (RopGAP4) increase as a consequence of Rop signaling under hypoxia. RopGAP4 negatively regulates Rop, possibly to minimize oxidative damage and carbohydrate consumption. The regulatory components that act downstream of Rop in hypoxic cells are unknown. DNA microarray-based analyses indicated that mRNAs encoding five of the twenty mitogen activated protein kinases (MAPKs) increase in abundance and association with polyribosomes during oxygen deprivation. In yeast and mammals, Rho-related GTPases are involved in networks that activate MAPK cascades. In plants, MAPK signaling is activated by ethylene, which is known to increase in response to hypoxia. In an in-gel kinase assay, a MAPK with electrophoretic mobility of ~49 kDa was activated within 30 minutes of hypoxia; this activation appeared higher in the ropgap4-1 loss-of-function mutant, which super-induces H₂O₂ level and ADH specific activity due to lack of negative feedback inhibition of Rop signaling. Seedlings deprived of oxygen in the presence of the MAPK kinase inhibitor, PD98058, had reduced induction of ADH specific activity. We are investigating whether Rop signaling and/or ethylene perception is responsible for MAPK activation in seedlings under hypoxia, and if MAPK cascades contribute to ADH and RopGAP4 mRNA accumulation and translation during hypoxia. Funded by NSF MCB-131486.