The expression of the genes involved in redox metabolism and hydrogen peroxide balance is associated with the resistance of cowpea [Vigna unguiculata (L.) Walp.] to the hemibiotrophic fungus Colletotrichum gloeosporioides.

Correlations between the transcriptional responses of genes that encode superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), and peroxiredoxin (Prx) enzymes and Colletotrichum gloeosporioides development in cowpea leaves were assessed. Each of these genes is involved in the redox metabolism and hydrogen peroxide balance. Although electron microscopy revealed that conidia adhered to and germinated on the leaf cuticle, the inoculated cowpea leaves did not show any characteristic anthracnose symptoms. The adhered and germinated conidia showed irregular surfaces and did not develop further. This was apparently due to increased leaf HO levels in response to inoculation with C. gloeosporioides. During the early stages post inoculation, cowpea leaves elevated the HO content and modulated the defense gene expression, as well as associated pathways. During the later stages, the increased expression of the CuZnSODI and CuZnSODII genes suggested an active superoxide dismutation to further elevate HO levels, which indicated that higher HO content may function as a toxic agent that kills the fungus. The second increase in HO production above the threshold level was correlated with the expression of the APXI, CATI, CATII, PrxIIBCD, and PrxIIE genes, which resulted in a coordinated pattern to establish an appropriate balance between HO generation and scavenging. Therefore, appropriate HO content in cowpea leaves inhibited C. gloeosporioides development and maintained intracellular redox homeostasis to avoid uncontrolled programmed cell death and necrosis in cowpea leaves.