Extreme resistance to Cowpea mosaic virus: molecular forms of the virus-encoded elicitors
G. BRUENING (1), J. Gao (1), Q. Fan (2) (1) Plant Pathology, University of California at Davis, U.S.A.; (2) Huazhong Agricultural University, China

Cowpea (Vigna unguiculata) is an important food legume in sub-Saharan Africa, valued for drought tolerance. The cowpea dominant locus we have designated as Cpa confers dominant extreme resistance against CPMV. 1 μg/mL of CPMV uniformly infects cowpea seedlings of susceptible (cpa/cpa) lines, but in lines with the Cpa locus, neither symptoms nor virions are observed, even at 10,000 μg/mL CPMV inoculum. The larger of two CPMV genomic RNAs, RNA1, encodes genes for replication designated, in 5’-3’ order, 32K, 60K, VPg, 24KPro, and 87KPol. VPg is part of the primer for genomic RNA synthesis. 24KPro is the protease of the virus. We reported previously that subclones of RNA1 encoding enzymically active 24KPro induced Cpa-dependent necrosis when expressed in cowpea leaves. Fusion protein VPg-24KPro and 24KPro were transiently expressed in cowpea seedling opposite half leaves. At 72 hr post inoculation, the opposite half-leaf necrotic areas were similar. At about 57 hr post inoculation, the VPg-24KPro necrotic area was several times the 24KPro necrotic area. Mutant VPg’s were prepared based on sequences from viruses not affected by Cpa. In transient expression experiments, VPg(V23N)-24KPro and 24KPro induced the same necrosis development at 57, and at 72 hr, indicating that a single VPg amino acid substitution was sufficient to erase the enhanced necrosis development characteristic of wildtype VPg-24KPro. These results suggest that VPg-24KPro is a more potent elicitor than 24KPro.

Abstract Number: P17-501
Session Type: Poster