Elicitation of induced systemic resistance of chili pepper by iturin A analogs derived from Bacillus vallismortis EXTN-1

Cyclic lipopeptides (CLPs) derived from plant growth-promoting rhizobacteria (PGPR) are well known as potential antifungal compounds. However, the physiological function of CLPs from Bacillus vallismortis strain EXTN-1 (EXTN-1) is still poorly understood. In this study, we proposed the potential role of iturin A analogs in modulation of induced systemic resistance (ISR) of chili pepper in response to Phytophthora capsici. Seven individual iturin A analogs were identified from EXTN-1, and iturin A analogs pre-treated plants resulted in a significant reduction of disease. However, no iturins directly inhibited growth of P. capsici in vitro antibiosis assay, indicating the existence of other possibilities for suppression of disease. The expression analysis of defense-related marker genes PR1, PR4, PR10, chitinase, peroxidase, and beta-1,3-glucanase revealed that transcript levels of these genes were dramatically up-regulated in iturin A analog treated plants after inoculation of P. capsici, suggesting that iturin-triggered plant systemic defense responses were involved in attenuating the disease symptoms. Collectively, our results clearly suggest that iturin A analogs from EXTN-1 are required for alleviation of P. capsici-mediated disease incidence.