Differential role for BiP3 in rice immune receptor-mediated resistance

Endoplasmic reticulum-bound chaperone luminal-binding protein 3 (BiP3) has been found to regulate the immunity mediated by the membrane-bound extracellular immune receptors Xa3/Xa26 and Xa21, that encode non-arginine-aspartate (non-RD) kinases, against the bacterial pathogen Xanthomonas oryzae pathovar oryzae (Xoo). In contrast, BiP3 appeared not to regulate the immunity mediated by the intracellular immune receptor Pi5, which encodes a nucleotide-binding domain and leucine-rich repeat (NB-LRR) protein, against the fungal pathogen Magnaporthe oryzae. To further examine this differential role for BiP3 in rice immunity, we generated transgenic rice plants overexpressing BiP3 in the background of the NB-LRR intracellular immune receptor Xa1 that confers resistance to Xoo. Our molecular genetic and phenotype analyses revealed that BiP3 overexpression does not affect Xa1-mediated rice resistance to Xoo. Our current results thus provide evidence that BiP3 regulates membrane-bound non-RD kinase-mediated, but not the intracellular NB-LRR-mediated, rice immune responses and that its function does not depend on the type of pathogen.