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

Authors: DHAR, NIKHILESH - University Of California; SHORT, DYLAN - University Of California; MAMO, BULLO - University Of California; CORRION, ALEX - Michigan State University; WAI, CHING - Michigan State University; Anchieta, Amy; VAN BUREN, ROBERT - Michigan State University; DAY, BRAD - Michigan State University; AJWA, HUSEIN - University Of California; SUBBARAO, KRISHNA - University Of California; Klosterman, Steven

Submitted to: Plant Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/9/2019
Publication Date: 4/11/2019
Citation: Dhar, N., Short, D.P., Mamo, B.E., Corrion, A.J., Wai, C.M., Anchieta, A.G., Van Buren, R., Day, B., Ajwa, H., Subbarao, K.V., Klosterman, S.J. 2019. Arabidopsis defense mutant ndr1-1 displays accelerated development and early flowering mediated by the hormone gibberellic acid. Plant Science. 285:200-213. https://doi.org/10.1016/j.plantsci.2019.04.006.
DOI: https://doi.org/10.1016/j.plantsci.2019.04.006

Interpretive Summary: The genetic network that controls plant defense and development is complex. We report that one of the more well-studied genes (NDR1) that has long been known as a key regulator of defense against various microorganisms, is also important in accelerating plant development in the model plant, Arabidopsis thaliana. NDR1 mutant plants showed strong accelerated initial growth as measured by main stem height and early flowering, although eventually the wild type plant height and seed production surpassed that of the NDR1 mutants. This suggests that normally, when NDR1 is not mutated, it acts as a negative regulator of plant growth and flowering. Through the use of the plant hormone gibberellic acid signaling inhibitor and direct exogenous applications of gibberellic acid, we also show that the effect of rapid early stem growth and flowering in the NDR1 mutant plants is clearly dependent upon the plant hormone giberellic acid. NDR1 and gibberellic acid responses are conserved in crop plants as well, but the relationship of NDR1 with defense have not been adequately studied in most of these systems. Future projects that seek to capitalize on development of resistance through manipulation of master regulators of plant defense such as NDR1 should also take into consideration the potential consequences on plant development.

Technical Abstract: NONRACE-SPECIFIC DISEASE RESISTANCE (NDR1) is a widely characterized gene that plays a key role in defense against multiple bacterial, fungal, oomycete and nematode plant pathogens. NDR1 is required for activation of resistance by multiple NB and LRR-containing (NLR) protein immune sensors and contributes to basal defense. The role of NDR1 in positively regulating salicylic acid (SA)-mediated plant defense responses is well documented. However, ndr1-1 plants flower earlier and show accelerated development in comparison to wild type (WT) Arabidopsis plants, indicating that NDR1 is a negative regulator of flowering and growth. Exogenous application of gibberellic acid (GA) further accelerates the early flowering phenotype in ndr1-1 plants, while the GA biosynthesis inhibitor paclobutrazol attenuated the early flowering phenotype of ndr1-1, but not to WT levels, suggesting partial resistance to paclobutrazol and enhanced GA response in ndr1-1 plants. Mass spectroscopy analyses confirmed that ndr1-1 plants have 30-40% higher levels of GA3 and GA4, while expression of various GA metabolic genes and major flowering regulatory genes is also altered in the ndr1-1 mutant. Taken together this study provides evidence of crosstalk between the ndr1-1-mediated defense and GA-regulated developmental programs in plants.