A plant virus uses plant metacaspase for its own benefit

A recent study by Pi et al. decoded previously unknown mechanism through which a virus manipulates the plant defense pathway for successful infection. Focusing on the interaction between barley and the devastating barley stripe mosaic virus (BSMV), researchers identified a critical regulatory hub centered on the cleavage of a specific RNA binding protein. In an uninfected plant, a plant metacaspase, MC4, which can cleave a nucleus-localized protein La1, remains in an inactive form. During virus infection, MC4 is activated and translocates to the nucleus where it cleaves La1. The cleaved La1 now translocates to the cytoplasm where it interacts with the purine-rich R-motif found on some defense RNAs, and this interaction leads to cap-independent translation of host defense mRNAs and antiviral immunity. This specialized translational pathway is crucial because it allows the plant to rapidly synthesize essential defense proteins, bypassing the standard cap-dependent machinery that viruses often manipulate for their own replication. However, BSMV employs a counter defense mechanism in which the γb protein of the BSMV bind to MC4 and keeps it in inactivated state. Thus the cleavage of La1 is hampered and the cap-independent translation of host defense mRNA also hampered. These insights open new avenues for engineering durable viral resistance in crop species. (Summary by Ved Prakash @vedjiwan) Science Advances 10.1126/sciadv.adv0819