Abstract
Colletotrichum higginsianum is an economically important pathogen that causes anthracnose disease in a wide range of cruciferous crops. Understanding the mechanisms of the cruciferous plant–C. higginsianum interactions will be important in facilitating efficient control of anthracnose diseases. The cAMP-PKA signaling pathway plays important roles in diverse physiological processes of multiple pathogens. C. higginsianum contains two genes, ChPKA1 and ChPKA2, that encode the catalytic subunits of cyclic AMP (cAMP)-dependent protein kinase A (PKA). To analyze the role of cAMP signaling pathway in pathogenicity and development in C. higginsianum, we characterized ChPKA1 and ChPKA2 genes, and adenylate cyclase (ChAC) gene. The ChPKA1 and ChAC deletion mutants were unable to cause disease and significantly reduced in hyphal growth, tolerance to cell wall inhibitors, conidiation, and appressorial formation with abnormal germ tubes, but they had an increased tolerance to elevated temperatures and exogenous H2O2. In contrast, the ChPKA2 mutant had no detectable alteration of phenotypes, suggesting that ChPKA1 contributes mainly to PKA activities in C. higginsianum. Moreover, we failed to generate ΔChPKA1ChPKA2 double mutant, indicating that deletion of both PKA catalytic subunits is lethal in C. higginsianum and the two catalytic subunits possibly have overlapping functions. These results indicated that ChPKA1 is the major PKA catalytic subunit in cAMP-PKA signaling pathway and plays significant roles in hyphal growth, pathogenicity, appressorial formation, conidiation, and stress tolerance in C. higginsianum.
Highlights
The hemibiotrophic fungus Colletotrichum higginsianum is an economically important pathogen that causes anthracnose disease on a wide range of cruciferous plants, including Brassica, Raphanus, and Arabidopsis thaliana (Narusaka et al, 2004; Yang et al, 2008; Hyde et al, 2009)
To better understand the cyclic AMP (cAMP)-protein kinase A (PKA) signaling pathway in C. higginsianum, we investigated the functions of PKA catalytic subunits ChPKA1 (CH063_00098) and ChPKA2 (CH063_12956), and adenylate cyclase ChAC (CH063_06008)
The SMART MODE analysis result indicates that both of ChPKA1 and ChPKA2 contain a Serine/Threonine protein kinase catalytic (S_TKc) domain and an Extension to Ser/Thr-type protein kinase (S_TK_X) domain (Supplementary Figure S2A), which plays a key role in catalysis of protein phosphorylation
Summary
The hemibiotrophic fungus Colletotrichum higginsianum is an economically important pathogen that causes anthracnose disease on a wide range of cruciferous plants, including Brassica, Raphanus, and Arabidopsis thaliana (Narusaka et al, 2004; Yang et al, 2008; Hyde et al, 2009). It was reported that cAMP signaling pathway is involved in the regulation of DON biosynthesis by two pathway-specific transcription factors TRI (trichothecene biosynthesis) 6 and TRI10 (Jiang et al, 2016) These findings suggest significant roles for cAMPPKA signaling pathway in multiple physiological processes of different microorganisms, especially during the steps of surface recognition and penetration which are critical in the infection cycle of many plant pathogenic fungi. Many studies have been done to elaborate cAMPPKA signaling pathway in other fungi, the specific roles of cAMP-PKA signaling for infection-related morphogenesis and infectious growth remain largely unknown in C. higginsianum. Our data indicate that cAMP-PKA signaling pathway plays essential roles in hyphal growth, stress tolerance, conidiation, appressorial formation, and pathogenicity in C. higginsianum
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