12.根こぶ病罹病カブのオーキシン生合成とホルモンクロストークにおけるニトリラーゼの役割(口頭発表)

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Plasmodiophora brassicae parasitizes cruciferous plant roots and manipulates indole-3-acetic acid (IAA) biosynthesis system of host plants to induce hypertrophy, called clubroot. We isolated three cDNAs encoding nitrilase from Brassica rapa (turnip), i.e. BrNIT-T1, BrNIT-T2 and BrNIT-T4. Enzyme analysis of recombinant proteins showed that BrNIT-T1 and BrNIT-T2 possess IAA synthetic activity, but BrNIT-T4 is involved in the plant cyanide detoxification pathway downstream of ethylene production. Realtime PCR analysis revealed specific involvement of BrNIT-T1 in clubroot initiation phase: in early-growing clubroot, BrNIT-T1 was strongly up-regulated but BrNIT-T2 and BrNIT-T4 were down-regulated. In maturing clubroot, not only BrNIT-T1 but also BrNIT-T2 and BrNIT-T4 were up-regulated. Free IAA level was transiently elevated at the early and later phases, despite a high IAA conjugation activity throughout disease development. Ethylene-forming activity was reduced during clubroot formation but subsequently increased, just like BrNIT-T4 expression. These results indicate a close relationship of the nitrilases to auxin and ethylene biosynthesis. Treatment of roots with cytokinin or jasmonic acid activated BrNIT-T1 or BrNIT-T2 expression, respectively. Thus, the two phytohormones may trigger IAA production in clubroot. Based on these observations, we propose a scheme regarding individual roles of the nitrilases in hormone crosstalk during clubroot initiation and maturation in turnip.
植物化学調節学会の論文
2007-10-05

12.根こぶ病罹病カブのオーキシン生合成とホルモンクロストークにおけるニトリラーゼの役割(口頭発表)

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