SsPtc3 Modulating SsSmk1-MAPK and Autophagy to Facilitate Growth and Pathogenicity in Sclerotinia sclerotiorum.

The compound appressoria of Sclerotinia sclerotiorum can produce cell wall-degrading enzymes, effectors and toxins, which promote penetration and the death of host cells. Subsequently, invasive hyphae (IH) branch rapidly as necrotrophic growth and disease symptoms are observed. S. sclerotiorum can respond to complex stresses and regulate its metabolism to adapt to the external environment. Here we demonstrated that type 2C Ser/Thr phosphatase (PP2C) SsPtc3 responds to nutritional, osmotic, cell wall and oxidative stresses. Loss of function ΔSsptc3 mutants displayed defects in mycelial growth, sclerotia formation and reduced virulence. Phosphoproteomic analyses revealed that SsPtc3 is involved in autophagy and MAPK signalling pathways. We obtained evidence that SsPtc3 negatively modulates the phosphorylation of SsSmk1. SsSmk1 is essential for mycelial growth, compound appressorium formation and pathogenicity, SsPtc3 modulated phosphorylation homeostasis of SsSmk1 to maintain hyphal growth. SsPtc3 interacted with SsAtg1 to influence autophagic flux under starvation. Taken together, these results reveal that SsPtc3 responds to various stresses that modulate autophagy and phosphorylation of SsSmk1-MAPK, which facilitates the growth and virulence of S. sclerotiorum.