Role of Arabidopsis LOR1 (LURP-one related one) in basal defense against Hyaloperonospora arabidopsidis

LOR1 is a member of a fifteen member gene family in Arabidopsis termed LOR (LURP-one related). Of the LOR gene family members, LOR1 shows strong constitutive expression based on microarray data against Hyaloperonospora arabidopsidis and Pseudomonas Syringe. LURP1 is another member of LOR family and a member of LURP gene cluster that shows an unusually pronounced transcriptional up-regulation in response to Hyaloperonospora arabidopsidis (Hpa). Mutation in LOR1 revealed a highly significant role of this gene in basal defense against Hpa whereas mutations in LURP1 resulted in reduced immunity mediated by the R-gene RPP5 against Hpa. Based on the resemblance of LOR1 protein to human Phospholipid scramlase1 (PLSCR1) stable CaMV35S:GFP-LOR1 and CaMV35S:GFP-LURP1 expression lines were created to analyze the subcellular localization of these proteins. GFP-LOR1 and GFP-LURP1 complemented loss of resistance in their respective mutant backgrounds. Like PLSCR, both GFP-LOR1 and GFP-LURP1 were found localized at the plasma membrane and in the nucleus but unlike PLSCR1 that is predominantly localized to the nucleus after cytokine induction, both GFP-LOR1 and GFP-LURP1 did not change their localization after infection with Hpa. LOR1 and LURP1 used as bait protein in yeast two hybrid system did not result in the identification of any interacting proteins from a screen of 2.3 × 105 cDNA for each from control and disease sampled plants treated with Hpa isolates.