The immune repressor BIR1 contributes to antiviral defense and undergoes transcriptional and post-transcriptional regulation during viral infections

Abstract

BIR1 is a receptor-like kinase that functions as a negative regulator of basal immunity and cell death in Arabidopsis. ? Using Arabidopsis thaliana and Tobacco rattle virus (TRV), we investigate the antiviral role of BIR1, the molecular mechanisms of BIR1 gene expression regulation during viral infections, and the effects of BIR1 overexpression on plant immunity and development. ? We found that SA acts as a signal molecule for BIR1 activation during infection. Inactivating mutations of BIR1 cause strong antiviral resistance that is not due to constitutive cell death or SA defense priming in the bir1-1 mutant. RNA-directed DNA methylation (RdDM) and posttranscriptional silencing are both required to negatively regulate BIR1 expression upon viral induction. BIR1 overexpression causes severe developmental defects, cell death and premature death that correlate with the constitutive activation of plant immune responses.