Functional and Promoter Analysis of ChiIV3, a Chitinase of Pepper Plant, in Response to Phytophthora capsici Infection

Abstract

Despite the involvement of many members of the chitinase family in plant immunity, the precise functions of the majority of the members remain poorly understood. Herein, the gene <i>ChiIV3</i> in <i>Capsicum annuum</i> encoding a chitinase protein containing a chitin binding domain and targeting to the plasma membrane was found to be induced by <i>Phytophthora capsici</i> inoculation (PCI) and applied chitin treatment. Besides its direct inhibitory effect on growth of <i>Phytophthora capsici</i> (<i>P. capsici</i>), ChiIV3 was also found by virus-induced gene silencing (VIGS) and transient overexpression (TOE) in pepper plants to act as a positive regulator of plant cell death and in triggering defense signaling and upregulation of <i>PR</i> (pathogenesis related) genes against PCI. A 5' deletion assay revealed that <i>pChiIV3</i>^{-712 to -459 bp} was found to be sufficient for <i>ChiIV3'</i> response to PCI. Furthermore, a mutation assay indicated that W-box^{-466 to -461 bp} in <i>pChiIV3</i>^{-712 to -459 bp} was noted to be the PCI-responsible element. These results collectively suggest that ChiIV3 acts as a likely antifungal protein and as a receptor for unidentified chitin in planta to trigger cell death and defense signaling against PCI.