B[beta]-aminobutyric acid-induced resistance in grapevine against downy mildew (Plasmopara viticola)

Plants respond to pathogen attack by activating signaling networks based on molecules such as salicylic acid (SA) and jasmonic acid (JA) followed by the accumulation of pathogenicity-related proteins, phytoalexins and other defense compounds. We used ß-aminobutyric acid (BABA), a non-protein amino acid to induce resistance in grapevine (Vitis vinifera) against downy mildew (Plasmopara viticola) and investigated the possible mechanisms responsible for the observed protective effect. Sporulation of P. viticola was reduced in BABA-treated seedlings as well as in leaf discs in both a susceptible variety (Chasselas) and a resistant variety (Solaris). Comparing different inducers, the best protection was achieved with BABA followed by JA, while BTH and abscisic acid (ABA) did not significantly increase the resistance. The potentiated accumulation of callose and lignin in BABA-treated plants was decreased by the co-application of DDG (an inhibitor of callose production) and AIP (an inhibitor of phenyl alanin ammonium lyase) respectively. PR-1, a marker gene for the SA pathway was expressed in both water and BABA-treated leaf discs, whereas PR-4 and LOX-9, markers for the JA pathway, showed potentiated expression in BABA-treated plants following P. viticola infection. Expression of PR-4 and LOX-9 in BABA-treated plants was decreased by the co-application of ETYA (a LOX inhibitor). The older, necrotic leaves as well as leaves infected with powdery mildew (Uncinula necator) accumulated defense-related genes in grapevine. Necrosis was observed in BABA-treated plants following infection with P. viticola. Accumulation of different phenolics and stilbenes in BABA-treated plants increased with time following infection. In the inoculation zones of leaf discs, accumulation of trans-resveratrol was much higher in BABA-treated than in control plants following infection. Outside of the inoculation zone accumulation levels of stilbenes were low. In seedlings, however, accumulation of trans-resveratrol was primed in both necrotic and non-necrotic zones, while trans-epsilon-viniferin was only primed in necrotic zones of BABA-treated plants. Furthermore, expression of the stilbene synthase gene (STS-1) was also higher in JA-treated plants than in BTH- and ABA-treated plants. The induction of STS-1 was observed in BABA-treated plants upon infection. Our results suggest that BABA-induced resistance (BABA-IR) involves priming of the JA signal transduction pathway and leads to a potentiated accumulation of callose, lignin, resveratrol and viniferins in grapevine following infection with downy mildew.

Thèse de doctorat : Université de Neuchâtel, 2005 ; 1823