Mutation of the rice XA21 predicted nuclear localization sequence does not affect resistance toXanthomonas oryzaepv.oryzae

BackgroundThe rice receptor kinase XA21 confers robust resistance to the bacterial pathogenXanthomonas oryzaepv.oryzae(Xoo). We previously reported that XA21 is cleaved in transgenic plants overexpressing XA21 with a GFP tag (Ubi-XA21-GFP) and that the released C-terminal domain is localized to the nucleus. XA21 carries a predicted nuclear localization sequence (NLS) that directs the C-terminal domain to the nucleus in transient assays, whereas alanine substitutions in the NLS disrupt the nuclear localization.MethodsTo determine if the predicted NLS is required for XA21-mediated immunityin planta, we generated transgenic plants overexpressing an XA21 variant carrying the NLS with the same alanine substitutions (Ubi-XA21nls-GFP).ResultsUbi-XA21nls-GFP plants displayed slightly longer lesion lengths, higherXoobacterial populations after inoculation and lower levels of reactive oxygen species production compared with theUbi-XA21-GFP control plants. However, theUbi-XA21nls-GFP plants express lower levels of protein than that observed inUbi-XA21-GFP.DiscussionThese results demonstrate that the predicted NLS is not required for XA21-mediated immunity.