AaPKAc Regulates Differentiation of Infection Structures Induced by Physicochemical Signals From Pear Fruit Cuticular Wax, Secondary Metabolism, and Pathogenicity of Alternaria alternata

Abstract

Alternaria alternata, the casual agent of black rot of pear fruit, can sense and respond to the physicochemical cues from the host surface and form infection structures during infection. To evaluate the role of cyclic AMP-dependent protein kinase (cAMP-PKA) signaling in surface sensing of A. alternata, we isolated and functionally characterized the cyclic adenosine monophosphate-dependent protein kinase A catalytic subunit gene (AaPKAc). Gene expression results showed that AaPKAc was strongly expressed during the early stages of appressorium formation on hydrophobic surfaces. Knockout mutants ΔAaPKAc were generated by replacing the target genes via homologous recombination events. We found that intracellular cAMP content increased but PKA content decreased in ΔAaPKAc mutant strain. Appressorium formation and infection hyphae were reduced in the ΔAaPKAc mutant strain, and the ability of the ΔAaPKAc mutant strain to recognize and respond to high hydrophobicity surfaces and different surface waxes was lower than in the wild type (WT) strain. In comparison with the WT strain, the appressorium formation rate of the ΔAaPKAc mutant strain on high hydrophobicity and fruit wax extract surface was reduced by 31.6 and 49.3% 4 h after incubation, respectively. In addition, AaPKAc is required for the hypha growth, biomass, pathogenicity, and toxin production of A. alternata. However, AaPKAc negatively regulated conidia formation, melanin production, and osmotic stress resistance. Collectively, AaPKAc is required for pre-penetration, developmental, physiological, and pathological processes in A. alternata.

Peel Diffusion and Antifungal Efficacy of Different Fungicides in Pear Fruit: Structure-Diffusion-Activity Relationships

“…It was indicated that the pear mesocarp was especially susceptible to Botrytis cinerea while the pear was immature [ 12 ]. The hydrophobicity of pear fruit cuticular wax is essential in facilitating fungal invasion by regulating the growth and differentiation of A. alternata [ 13 , 14 , 15 ]. Thus, the diffusion capacity of fungicides from peel to the external part of the pear mesocarp may play an important role in their control efficacy.…”

Antibacterial insights into alternariol and its derivative alternariol monomethyl ether produced by a marine fungus

“…To delete the omtI gene from the genome of A. alternata FB1, a homologous recombination method was employed ( 66 ). Due to the fact that the wild-type A. alternata FB1 is sensitive to 100 µg/mL hygromycin, we could therefore operate gene knockout in the medium containing hygromycin.…”

AaCaMKs Positively Regulate Development, Infection Structure Differentiation and Pathogenicity in Alternaria alternata, Causal Agent of Pear Black Spot

“…A. alternata growth and conidiation were detected as previously described [ 10 ]. Precisely, the PDA medium was inoculated with 2 µL spore suspensions (1 × 10 5 spores mL −1 ) of WT A. alternata , ΔAaCaMKs and ΔAaCaMKs -C strains and incubated at 28 °C.…”

“…In addition, the hydrophobic and pear wax substrates stimulate the differentiation of the A. alternata infection structure [ 9 ]. At the same time, AaPKAc and AaPDEL/AaPDEH in cAMP/PKA pathway [ 10 , 11 ], AaPLCs in Ca 2+ signaling pathway [ 12 ], AaHog1 in the MAPK cascades pathway [ 13 ], and transmembrane protein AaSho1 [ 14 ] are involved in the differentiation of A. alternata infection structure under hydrophobic and pear wax substrates. However, how the pathogen responds to host epidermal signals until the initiation of the infection needs to be elucidated further.…”