Publication no. M-2002-1001-01R

The P34 Syringolide Elicitor Receptor Interacts with a Soybean Photorespiration Enzyme, NADH-Dependent Hydroxypyruvate Reductase. Yasushi Okinaka (1), Ching-Hong Yang (1), Eliot Herman (2), Anthony Kinney (3), and Noel T. Keen (1). (1) Department of Plant Pathology and Center for Plant Cell Biology, University of California, Riverside 92521 U.S.A.; (2) Plant Genetics Unit, USDA-ARS Donald Danforth Plant Science Center, 975 N. Warson Rd., St. Louis, MO 63132 U.S.A.; (3) Dupont Experimental Station, Rt. 141 and Henry Clay Road, Wilmington, DE 19880 U.S.A. MPMI 15:1213-1218. Submitted 6 May 2002. Accepted 6 August 2002. Copyright 2002 The American Phytopathological Society.

The syringolide receptor P34 mediates avrD-Rpg4 gene-for-gene complementarity in soybean. However, the mechanism underlying P34 signal transmission after syringolide binding is unknown. In an effort to identify a second messenger for P34, soybean leaf proteins were run though a P34-affinity column. A 42-kDa protein which specifically bound to the column was identified as a putative plant NADH-dependent hydroxypyruvate reductase (HPR) by N-terminal peptide sequencing. HPR is an important enzyme involved in the plant photorespiration system. Screening of a soybean cDNA library yielded two distinct HPR clones that encoded proteins with 97% identity (P42-1 and P42-2). Surprisingly, only P42-2 displayed good binding with P34 in a yeast two-hybrid assay, indicating that P42-2, but not P42-1, is a potential second messenger for P34. Glycerate and its analogs, which are utilized in the photorespiration system, were tested for their inhibitory effect on syringolide-induced hypersensitive response (HR) to evaluate the biological significance of P42-2. Interestingly, the downstream products of HPR (glycerate and 3-phosphoglycerate) inhibited HR but the upstream compounds (hydroxypyruvate or serine) did not have a significant effect on HR. These results suggest that P42-2 is a primary target for a P34/syringolide complex and that P42-2 binding with the complex probably induces HR by inhibiting one or more HPR functions in soybean.