Cs02526 effector: A double-edged sword in mulberry–pathogen interactions

For millions of years, there has been a subtle yet intense competition between pathogens and plants.Phytopathogens proliferate by usurping nutrients from plant tissues while host plants deploy diverse defense mechanisms to impede pathogen proliferation.Plants defend themselves using pattern recognition receptors (PRRs) to recognize pathogen-associated molecular patterns (PAMP), initiating PAMP-triggered immunity (PTI) to restrict pathogen growth.As a counterresponse, phytopathogens translocate effector proteins into plant cells to sabotage the host cellular machinery and promote infection (Khan, 2018).However, these effectors can be recognized by host cytosolic NOD-like receptors (NLRs), activating effector-triggered immunity (ETI) (Jones and Dangl, 2006; Cui et al., 2015).Extensive studies have highlighted the crucial role of phytopathogen effectors in plant infestation, as these effectors target various host macromolecules and manipulate them through diverse enzymatic activities.Thus, understanding the effector function is crucial for developing novel strategies to manage plant diseases.Mulberry (Morus spp.) trees are economically important, particularly in the silkworm (sericulture) industry, and their fruits are rich in nutrients and anthocyanins (Li et al., 2020).However, mulberry sclerotinia disease, primarily caused by the necrotrophic fungus Ciboria shiraiana, poses a significant threat, leading to substantial annual losses in mulberry fruit yield (Zhang et al., 2021; Zhu et al., 2021).In the current issue of Plant Physiology, Zhang et al.(2024) shed light on potential solutions by identifying key effectors in C. shiraiana and investigating their impact on plant immune responses.The authors initially identified potential effectors in C. shiraiana by analyzing its genome followed by transiently expressing some of these effectors in Nicotiana benthamiana plants.One of these effectors, Cs02526, induced cell death in N. benthamiana.To further validate this cell death response, Zhang and coworkers assessed electrolyte leakage and the expression levels of hypersensitive response (HR)-specific marker genes in N. benthamiana leaves agroinfiltrated with the Cs02526 construct.The findings revealed a significant increase in electrolyte leakage and the expression of the HR-marker genes in the Cs02526 agroinfiltrated leaves compared to the control, indicating that Cs02526 can induce cell death in N. benthamiana.Further, investigations demonstrated that Cs02526 could also induce cell death in various plant species, including tobacco, tomato, strawberry, and mulberry leaves, suggesting its broad activity across different plants.