Multifunctionality of AsCFEM6 and AsCFEM12 effectors from the potato early blight pathogen Alternaria solani

Authors: QIU, CHAODONG - Anhui Agricultural University; Halterman, Dennis; ZHANG, HUAJIAN - Anhui Agricultural University; LIU, ZHENYU - Anhui Agricultural University

Submitted to: International Journal of Biological Macromolecules
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/1/2023
Publication Date: 12/2/2023
Citation: Qiu, C., Halterman, D.A., Zhang, H., Liu, Z. 2023. Multifunctionality of AsCFEM6 and AsCFEM12 effectors from the potato early blight pathogen Alternaria solani. International Journal of Biological Macromolecules. 0141-8130/© 2023. https://doi.org/10.1016/j.ijbiomac.2023.128575.
DOI: https://doi.org/10.1016/j.ijbiomac.2023.128575

Interpretive Summary: Fungal plant pathogens secrete proteins that are Common in several Fungal Extracellular Membrane (CFEM) that play a role manipulating plant immunity and contribute to pathogen virulence. Little is known about these proteins and their functions in Alternaria solani, the necrotrophic fungal pathogen causing potato early blight. To identify candidate CFEM genes, we looked at the genome sequences of A. solani. This led to the identification of 12 genes encoding CFEM proteins (termed AsCFEM1-AsCFEM12) and 6 of them were confirmed to be putative secreted proteins. Expression of these genes in plants revealed that AsCFEM6 and AsCFEM12 have are able to activate plant defense responses in different botanical families, some of which are not normally hosts for this pathogen. Targeted gene disruption of AsCFEM6 and AsCFEM12 resulted in a change in the development of spores, a significant reduction of virulence on potato and eggplant, an increase in resistance to fungicide, a variation in iron acquisition and utilization, and in the formation of melanin, which is important in long-term viability of spores. Targeted mutations within the AsCFEM proteins identified specific regions that are important in some of these functions. Knowledge of A. solani genes that are involved in causing disease is very limited. The identification of AsCFEM6 and AsCFEM12 as contributors to disease in potato is an important step towards understanding how this fungus manipulates host metabolism and will impact the identification of plant genes that can counteract their function to increase resistance.

Technical Abstract: Plant pathogens secrete fungal-specific common in several fungal extracellular membrane (CFEM) effectors to manipulate host immunity and contribute to their virulence. Little is known about effectors and their functions in Alternaria solani, the necrotrophic fungal pathogen causing potato early blight. To identify candidate CFEM effector genes, we mined A. solani genome databases. This led to the identification of 12 genes encoding CFEM proteins (termed AsCFEM1-AsCFEM12) and 6 of them were confirmed to be putative secreted effectors. In planta expression revealed that AsCFEM6 and AsCFEM12 have elicitor function that triggers plant defense response including cell death in different botanical families. Targeted gene disruption of AsCFEM6 and AsCFEM12 resulted in a change in spore development, significant reduction of virulence on potato and eggplant susceptible cultivars, increased resistance to fungicide stress, variation in iron acquisition and utilization, and the involvement in 1,8-dihydroxynaphthalene (DHN) melanin biosynthesis pathway. Using maximum likelihood method, we found that positive selection likely caused the polymorphism within AsCFEM6 and AsCFEM12 homologs in different Alternaria spp. Site-directed mutagenesis analysis indicated that positive selection sites within their CFEM domains are required for cell death induction in Nicotiana benthamiana and are critical for response to abiotic stress in yeast. These results demonstrate that AsCFEM effectors possess additional functions beyond their roles in host plant immune response and pathogen virulence.