IRE1-dependent signaling arm of the unfolded protein response balances bifurcating influences on potexvirus replication/gene expression and virus cell-to-cell movement.

Our study delves deep into the interactions between Plantago asiatica mosaic virus and Arabidopsis's endoplasmic reticulum (ER) stress machinery.  The inositol-requiring enzyme 1 (IRE1) is a key sensor of stress and errors in protein folding in the ER.  While there are three isoforms of IRE1, only two are recognized as ER stress sensors, however, all three have ribonuclease activities attaching a range of RNA substrates for degradation (RIDD) and for specific splicing of the bZIP60 mRNA to produce a functional transcription factor names bZIP60S.  The full-length bZIP60U is a membrane-bound protein whose function is largely unknown. This study was undertaken to elucidate the distinct roles of the IRE1A, B, and C as well as bZIP60 in constraining PlAMV accumulation, cell-to-cell and vascular movement.  Using KO mutant Arabidopsis lines we show that these 4 factors limit host susceptibility to infection by reducing the ability to establish infection foci.  The bZIP60 factor plays a unique role in restricting virus cell-to-cell and systemic movement, which may be controlled by both the bZIP60S and bIZP60U factors.  We will present evidence that bZIP60U interacts with the potexvirus TGB3, that IRE1A, B, and C have overlapping abilities to influence virus infection.   We also present evidence that a potato bZIP60 can complement the loss of function defects in Arabidopsis.  These data led to a new and unique model for the roles of the IRE1-led arm of the UPR in potexvirus infection.