| Budget Amount *help |
¥3,600,000 (Direct Cost: ¥3,600,000)
Fiscal Year 2001: ¥1,000,000 (Direct Cost: ¥1,000,000)
Fiscal Year 2000: ¥2,600,000 (Direct Cost: ¥2,600,000)
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| Research Abstract |
Ralstonia solanacearum OE1-1 (OE1-1) is pathogenic to tobacco. A popA-mutant of OE1-1 with Tn4431, 31b, grew in and moved through vascular bundle in tabacco but lost its pathogenicity to the tobacco plants, when inoculated by root dipping and infiltrated into tobacco leaves. However, the mutant showed pathogenicity to the tobacco plants inoculated into vascular bundle through cut stems. The mutated PopA protein of 31b was composed of 319 amino acid residues, and the amino acid sequence of 1-307 residues was identical to that of PopA protein of OE1-1. A popABC operon-deleted mutant of OE1-1, △ABC-OE, showed pathogenicity similarly as the parent strain. On the other hand, a transformant, △OE-p31b, of △ABC-OE with p31b including a mutated popA showed pathogenicity similarly as 31b. The analysis of RT-PCR showed that popA in OE1-1 was expressed 3 hr after infiltration with into tobacco leaves (HIT), and mutated popA in 31b and △OE-p31b was also expressed 3 HIT. When a transformant of OE1-1
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, Papa with pPapa containing popA fused to a constitutively active promoter infiltrated into tobacco leaves, popA was expressed 1 HAI. Papa did not grow in inoculated area and move to periphery, resulting in loss of its pathogenicity to tobacco plants when inoculated using the root dipping and infiltrated into tobacco leaves. However, Papa retained its pathogenicity when directly inoculated into vascular bundle. These results indicate that PopA protein is not directly involved in the bacterial pathogenicity because popA is not expressed until 3 HAI. However, when popA is expressed 1 HAI, PopA can function as a negative effector of the bacterial proliferation in the host plants, resulting in loss of the bacterial pathogenicity. Moreover, C-terminus-mutated PopA protein makes influences on the bacteria-plant interactions from 3 HAI to the bacterial arrival to vascular bundle, resulting in negative regulation on the bacterial pathogenicity. Taken together, the bacterial proliferation and movement into vascular bundle immediately after invasion, which are essential factors of its pathogenicity, depend on interactions between R solariacearum and host plants during 3 hr after the bacterial invasion Moreover, development of wilt symptom depends on the interactions in intercellular spaces of roots and mesophyll until the bacterial infection to vascular bundle. Less
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