Phospholipase C From Alternaria alternata Is Induced by Physiochemical Cues on the Pear Fruit Surface That Dictate Infection Structure Differentiation and Pathogenicity

Abstract

To investigate the mechanisms of phospholipase C (PLC)-mediated calcium (Ca²⁺) signaling in <i>Alternaria alternata</i>, the regulatory roles of PLC were elucidated using neomycin, a specific inhibitor of PLC activity. Three isotypes of PLC designated <i>AaPLC1</i>, <i>AaPLC2</i>, and <i>AaPLC3</i> were identified in <i>A. alternata</i> through genome sequencing. qRT-PCR analysis showed that fruit wax extracts significantly upregulated the expression of all three PLC genes <i>in vitro</i>. Pharmacological experiments showed that neomycin treatment led to a dose-dependent reduction in spore germination and appressorium formation in <i>A. alternata</i>. Appressorium formation was stimulated on hydrophobic and pear wax-coated surfaces but was significantly inhibited by neomycin treatment. The appressorium formation rates of neomycin treated <i>A. alternata</i> on hydrophobic and wax-coated surfaces decreased by 86.6 and 47.4%, respectively. After 4 h of treatment, exogenous CaCl₂ could partially reverse the effects of neomycin treatment. Neomycin also affected mycotoxin production in alternariol (AOH), alternariol monomethyl ether (AME), altenuene (ALT), and tentoxin (TEN), with exogenous Ca²⁺ partially reversing these effects. These results suggest that PLC is required for the growth, infection structure differentiation, and secondary metabolism of <i>A. alternata</i> in response to physiochemical signals on the pear fruit surface.