Ectopic expression of Ralstonia solanacearum effector protein PopA early in invasion results in loss of virulence.
Ralstonia solanacearum OE1-1 (OE1-1) is pathogenic to tobacco. The type III-secreted effector protein popA of OE1-1 showed 97.6% identity to popA of R. solanacearum GMI1000, which is not pathogenic to tobacco. Reverse transcription-polymerase chain reaction analysis showed that popA in OE1-1 was expressed at 3 h after inoculation (HAI), but not before, in infiltrated-tobacco leaves. Pathogenicity analysis using a popABC operon-deleted mutant of OE1-1 (deltaABC) showed that popABC is not directly involved in the pathogenicity of OE1-1. When Papa, which constitutively expresses popA, was infiltrated into tobacco leaves, popA was expressed by 0.5 HAI. Papa could no longer multiply or spread in tobacco leaves and was no longer virulent. Moreover, the hypersensitive response (HR) and expression of HR-related genes were not induced in Papa-infiltrated leaves. Papa was also avirulent in a tobacco root-dipping inoculation assay. These results suggest that the expression of popA in Papa immediately after invasion triggers the suppression of bacterial proliferation and movement, resulting in loss of virulence. However, Papa retained its virulence when directly inoculated into xylem vessels. This result suggests that tobacco plants can recognize PopA when it is expressed early in disease development, and respond with an effective defense in the intercellular spaces.
Laboratory of Plant Pathology and Biotechnology, Kochi University, Nankoku, Kochi, 783-8502, Japan.
Ayami
A
Kanda
Masahiko
M
Yasukohchi
Kouhei
K
Ohnishi
Akinori
A
Kiba
Tetsuro
T
Okuno
Yasufumi
Y
Hikichi
D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism; D015964:Gene Expression Regulation, Bacterial; D018506:Gene Expression Regulation, Plant; D016946:Gram-Negative Aerobic Rods and Cocci / Q000235:genetics* / Q000472:pathogenicity; D007113:Immunity, Innate / Q000235:genetics; D008969:Molecular Sequence Data; D010935:Plant Diseases / Q000235:genetics / Q000382:microbiology; D018515:Plant Leaves / Q000235:genetics / Q000382:microbiology; D014026:Nicotiana / Q000235:genetics / Q000382:microbiology*; D014774:Virulence / Q000235:genetics
D001426:Bacterial Proteins; C085878:PopA1 protein, Ralstonia solanacearum