ZfpA-regulated chitin synthesis in Aspergillus fumigatus hyphae determines fungicidal tip lysis by FksA-targeting antifungals

Aspergillus fumigatus poses a serious threat to the health of a growing immunocompromised population. Invasive aspergillosis infections have one of the highest mortality rates of any disease, and treatment options are extremely limited. The β-1,3-glucan synthase-inhibiting echinocandins are one of only three classes of drugs approved to treat these infections. However, their clinical efficacy against Aspergillus is considered fungistatic. Disruption of proper cell wall synthesis at the growing tip of hyphae can result in the lysis of the apical tip compartment. The oxylipin-associated transcription factor ZfpA is known to regulate a growth program in response to echinocandins that blocks the tip lytic action of these drugs. It is known that ZfpA positively regulates hyphal cell wall chitin, which is also found to be upregulated in response to echinocandins. Here, we find that ZfpA is activated broadly by cell wall stress but confers protection against only β-1,3-glucan targeting antifungals including the lipopeptide echinocandins and the novel terpene fungerp enfumafungin. In addition, we show that at least four of the eight chitin synthases in A. fumigatus are important for echinocandin tolerance, contributing to a multifactorial response to tolerate β-1,3-glucan depletion downstream of the transcription factor ZfpA. We find that the enzymes ChsF and ChsG, specifically, play opposing roles in resistance to apical tip lysis due to inhibition of β-1,3-glucan synthase.