Abstract
Exogenous ABA application enhances rice susceptibility to M.grisea. We previously reported that ABA suppressed the expression of WRKY45 and OsNPR1, the two key regulatory factors in the rice SA signaling pathway. In this study, we analyzed the influences of reduced ABA levels and ABA signaling to defense responses around the penetration sites during early stages of M. grisea infection using transgenic rice plants that transiently express an ABA catabolic enzyme (OsABA8ox1) or a dominant-negative mutant form of ABA signaling component [OsABI(G-A)] under the control of DEX-inducible promoter.
ABA treatment of rice prior to, but not posterior to, M. grisea inoculation resulted the increase of lesion numbers. Similarly, DEX-induced expression of OsABA8ox1 or OsABI(G-A) prior to M. grisea inoculation reduced the lesion numbers but their expression after fungus inoculation did not. These results suggest that endogenous level of ABA in early stage of infection is important for the induction of defense responses. Microscopic observation revealed the suppression of hyphal invasion into host cells, enhancement of autofluorescence, and reduction of callose deposition at penetration sites.
