A recessive mutation in the Arabidopsis SSI2 gene confers SA- and NPR1-independent expression of PR genes and resistance against bacterial and oomycete pathogens.
The Arabidopsis thaliana NPR1 gene is required for salicylic acid (SA)-induced expression of pathogenesis-related (PR) genes and systemic acquired resistance. However, loss-of-function mutations in NPR1 do not confer complete loss of PR gene expression or disease resistance. Thus these responses also can be activated via an NPR1-independent pathway that currently remain to be elucidated. The ssi2-1 mutant, identified in a genetic screen for suppressors of npr1-5, affects signaling through the NPR1-independent defense pathway(s). In comparison with the wild-type (SSI2 NPR1) plants and the npr1-5 mutant (SSI2 npr1-5), the ssi2-1 npr1-5 double mutant and the ssi2-1 NPR1 single mutant constitutively express PR genes [PR-1, BGL2 (PR-2) and PR-5]; accumulate elevated levels of SA; spontaneously develop lesions; and possess enhanced resistance to a virulent strain of Peronospora parasitica. The ssi2-1 mutation also confers enhanced resistance to Pseudomonas syringae pv. tomato (Pst); however, this is accomplished primarily via an NPR1-dependent pathway. Analysis of ssi2-1 NPR1 nahG and ssi2-1 npr1-5 nahG plants revealed that elevated SA levels were not essential for the ssi2-1-conferred phenotypes. However, expression of the nahG transgene did reduce the intensity of some ssi2-1-conferred phenotypes, including PR-1 expression, and disease resistance. Based on these results, SSI2 or an SSI2-generated signal appears to modulate signaling of an SA-dependent, NPR1-independent defense pathway, or an SA- and NPR1-independent defense pathway.
Shah
J
J
Waksman Institute and Department of Molecular Biology and Biochemistry, Rutgers, The State University of New Jersey, 190 Frelinghuysen Road, Piscataway, NJ 08855-8020, USA. shah@ksu.edu
Kachroo
P
P
Nandi
A
A
Klessig
D F
DF
D017360:Arabidopsis / Q000235:genetics* / Q000382:microbiology; D029681:Arabidopsis Proteins; D015152:Blotting, Northern; D018506:Gene Expression Regulation, Plant; D007113:Immunity, Innate / Q000235:genetics; D009154:Mutation; D009868:Oomycetes / Q000472:pathogenicity*; D010641:Phenotype; D010935:Plant Diseases / Q000235:genetics*; D010940:Plant Proteins / Q000235:genetics* / Q000378:metabolism; D011549:Pseudomonas / Q000472:pathogenicity*; D018749:RNA, Plant / Q000032:analysis; D020156:Salicylic Acid / Q000378:metabolism*; D014774:Virulence
D029681:Arabidopsis Proteins; C105496:NPR1 protein, Arabidopsis; D010940:Plant Proteins; D018749:RNA, Plant; D020156:Salicylic Acid