Abscisic Acid–Responsive 18 (CaABR18) Protein from Chickpea Inhibits the Growth of the Wilt-Causing Fusarium oxysporum f. sp. ciceri Race1

Abstract

Multigene family pathogenesis-related-10 (PR-10) proteins are indispensable for initiation of plant defense reactions upon pathogen attack. Here, we report the isolation and differential induction of Cicer arietinum L. ABR18 (CaABR18) gene in susceptible and resistant chickpea upon exposure to Fusarium oxysporum f. sp. ciceri Race1 (Foc1). Further, sequence analysis and structural studies confirmed that CaABR18 protein possesses conserved glycine-rich P-loop motif and Betv 1 domain, which are common to many PR-10 family proteins. CaABR18 gene was found to be expressed in all the developing organs, with higher abundance in the mature leaves. Foc1 inoculation resulted in higher expression of CaABR18 gene in the resistant chickpea compared with susceptible one. CaABR18 protein induction was also observed by salicylic acid (SA) or abscisic acid (ABA) treatment. Biochemical analysis was performed using in vitro purified histidine-tagged recombinant ABR18 protein. Purified recombinant protein exhibits in vitro RNase and DNase activities. Application of recombinant ABR18 protein increases PI/SYTOX green uptake and nuclear disintegration and suppresses the growth of Foc1 hyphae in vitro. Agrobacterium-mediated transient expression of ABR18-YFP triggers reactive oxygen species (ROS) formation and cell death in Nicotiana benthamiana leaves. The fusion protein is shown to be targeted to the host nucleus. Taken together, our results revealed that CaABR18 imparts Fusarium resistance in chickpea by RNA/DNA degradation within host cells leading to programmed cell death (PCD) and also shows antifungal activity through its proper internalization, increasing membrane permeability and nuclear disintegration of Foc1.