Rice Root-knot Nematode Down Regulates GA-Gene to Establish Infection

Abstract

Experiments were conducted to observe the role of gibberellin (GA) in the response of rice to infection by rice root-knot nematode, Meloidogyne graminicola. Gibberellin might have a negative effect on defence in Nipponbare against M. graminicola. On the other hand, an inhibitory effect to M. graminicola in Taichung 65 (wild type) was found when GA was applied exogenously. Galling was significantly and reproducibly lower in mutants, whether it was GA insensitive or GA deficient, than in Taichung 65. There were even significantly lower galls in these GA deficient mutants after GA treatment than in non-treated mutant plants. The expression of GA signaling gene Osgid1-7 was significantly higher only in whole root at 2 dpi (days post inoculation) but not in leaves or root tips. Even this gene was not differentially expressed in root and leaf tissues at later stage (6 dpi days post inoculation) of infection. The nematode inhibited biosynthesis of OsGA20ox in leaves at 2 dpi and, in both of leaves and roots at 6 dpi. The GA response gene AK073385 was also less expressed in root tip at 6 dpi (days post inoculation). These might help M. graminicola to continue their infection in Taichung 65.