A novel regulatory network controlling immune repression during viral infections, and its impact on plant homeostasis and fitness

The group of Gene regulation and stress led by Dr. César Llave at the Center for Biological Research of the CSIC has recently shown that the BIR1 immune repressor is a negative regulator of the plant's defenses against viral infections. These results have been published in the journal New Phytologist and researchers from the University of Málaga and the University of Michigan (USA) are collaborators.

In the absence of pathogens, the immune response is under a strict negative control since the constitutive activation of the defenses has deleterious effects on plant fitness and development. The membrane protein BIR1 is a receptor-like kinase that plays a key role in this process by blocking the function of several ligand-binding immune receptors, thus preventing the activation of multiple immune signaling cascades. The study by Irene Guzmán-Benito and collaborators demonstrates that both the loss of BIR1 function and its overexpression are associated with the appearance of severe developmental defects, cell death and premature wilt that in turn correlate with the constitutive activation of defenses. These findings indicate that the expression of BIR1 must be regulated within optimal functional thresholds that guarantee an appropriate control of the immune response. In this regard, this work reveals a complex regulatory network that involves both the salicylic acid-dependent transcriptional activation of BIR1, and its repression by epigenetic silencing and post-transcriptional mRNA cleavage.

These findings demonstrate that beyond being an effective defensive barrier against extracellular pathogenic microorganisms such as fungi, bacteria and oomycetes, basal innate immunity also plays a relevant role in resistance to intracellular parasites such as viruses. In addition, they show that the regulation of BIR1 during infections is essential to ensure the correct development of the plant and to preserve plant fitness. This work provides novel mechanistic insights into the regulation of BIR1 homeostasis that may be common for other plant immune components.

Referencia: The immune repressor BIR1 contributes to antiviral defense and undergoes transcriptional and post-transcriptional regulation during viral infections. Guzmán-Benito I, Donaire L, Amorim-Silva V, Vallarino JG, Esteban A, Wierzbicki AT, Ruiz-Ferrer V, Llave C. New Phytologist (2019) May 20. https://doi.org/10.1111/nph.15931