Modulation of fungal virulence through CRZ1 regulated F-BAR-dependent actin remodeling and endocytosis in chickpea infecting phytopathogen Ascochyta rabiei

Abstract

Polarized hyphal growth of filamentous pathogenic fungi is an essential event for host penetration and colonization. The long-range early endosomal trafficking during the hyphal growth is crucial for nutrient uptake, sensing of host-specific cues, and regulation of effector production. Bin1/Amphiphysin/Rvs167 (BAR) domain-containing proteins mediate fundamental cellular processes, including membrane remodeling and endocytosis. Here, we identified an F-BAR domain protein (ArF-BAR) in the necrotrophic fungus Ascochyta rabiei and demonstrate its involvement in endosome-dependent fungal virulence on the host plant, Cicer arietinum. We show that ArF-BAR regulates endocytosis at the hyphal tip, localizes to the early endosomes, and is involved in actin dynamics. Functional studies involving gene knockout and complementation experiments reveal that ArF-BAR is essential for virulence. The loss-of-function of ArF-BAR results in delayed formation of first septa from the hyphal tip, crucial for host penetration and proliferation. ArF-BAR was induced in response to oxidative stress and infection and localized to endocytic vesicles within the fungal hyphae. We also show that ArF-BAR is able to tubulate synthetic liposomes, suggesting the functional role of F-BAR domain in membrane tubule formation in vivo. Further, our studies identified a stress-induced transcription factor, ArCRZ1 (Calcineurin-responsive zinc finger 1) as key regulator for transcriptional reprogramming of ArF-BAR. We propose a model in which ArCRZ1 functions upstream of ArF-BAR to regulate fungal pathogenesis through a mechanism that involves membrane remodeling and actin cytoskeleton regulation. Author summaryBAR-domain superfamily is known to mold amorphous lipid bilayer into defined tubular shapes and critical for endosome formation and trafficking. Although these processes are studied earlier in the context of their structural and biochemical properties, there is limited evidence on the direct role of F-BAR domain proteins in the pathophysiological development of other economically important fungi. Our study assumes functional significance for plant infection as we identified an F-BAR domain-containing protein that is regulated by a distinct transcriptional network. We characterized F-BAR in a necrotrophic fungal pathogen, Ascochyta rabiei that causes the Ascochyta blight (AB) disease in chickpea plants. Additionally, we have also identified a calcium-regulated CRZ1 transcription factor that regulates the transcription of ArF-BAR. Our study will help to understand the complex interplay underlying the endosome formation required for fungal virulence.