Arabidopsis defense mutant ndr1-1 displays accelerated development and early flowering mediated by the hormone gibberellic acid

Hormone Signaling and Its Interplay With Development and Defense Responses in Verticillium-Plant Interactions

“…SA pathway components are required for resistance against Verticillium spp. in Arabidopsis , tomato, and cotton ( Johansson et al, 2006 ; Fradin et al, 2009 ; Gao et al, 2011 ; Dhar et al, 2019 ). In Arabidopsis-V. longisporum interactions, SA levels have been shown to be augmented in an Arabidopsis genotype-specific manner following inoculations with the pathogen ( Haffner et al, 2014 ).…”

“…The plant nonrace specific disease resistance 1 ( NDR1 ) gene is central to SA-mediated defense responses and is required for resistance against plant pathogenic bacteria, fungi, and nematodes ( Century et al, 1995 ; Gao et al, 2011 ; Dhar et al, 2019 ). NDR1 is required for a reactive oxygen species (ROS)-dependent hypersensitive response (HR) and the accumulation of SA in response to pathogens ( Century et al, 1995 ).…”

“…Challenge by a pathogen results in a “growth versus defense conundrum” in plants ( Chini et al, 2007 ; Huot et al, 2014 ), including in Verticillium -host interactions ( Dhar et al, 2019 ). In Verticillium wilt of oilseed rape, the transition to reproductive stage is critical for the spread of the pathogen and appearance of disease symptoms, while in cotton, the severity of Verticillium wilt increases in the field is concomitant with the transition to flowering ( Li et al, 2014 ).…”

“…The well-characterized Arabidopsis ndr1-1 defense mutant ( Century et al, 1995 ; Aarts et al, 1998 ), which confers increased susceptibility to Verticillium infection, was shown to display early flowering ( Figure 2A top panel) linked to enhanced expression of GA biosynthesis genes, increased bioactive GA in planta as well as a reduction in the levels of DELLA components ( Dhar et al, 2019 ). Because NDR1 is central to SA-mediated defense responses, the establishment of SAR, and the HR response against pathogens ( Century et al, 1995 ; Aarts et al, 1998 ), this new finding raises the exciting possibility that increased susceptibility in ndr1-1 might not only be due to its inability to accumulate SA but also due to the fact that enhanced GA signaling in this mutant might also contribute toward this outcome ( Figure 2B ).…”

“…A similar phenotype occurs in plants grown under the long day conditions (14/10 h light/dark cycle). Reproduced with permission ( Dhar et al, 2019 ). Arabidopsis ndr1-1 mutants are susceptible to Verticillium longisporum ( Vl Bob70) and flower earlier than the corresponding uninfected plants.…”