Oleic acid-dependent modulation of Nitric oxide associated 1 protein levels regulates nitric oxide-mediated defense signaling in Arabidopsis

Authors: MANDAL, MIHIR - University Of Kentucky; CHANDRA-SHEKARA, AC - University Of Kentucky; JEONG, RAE-DONG - University Of Kentucky; YU, KESHUN - University Of Kentucky; ZHU, SHIFENG - University Of Kentucky; CHANDA, BIDISHA - University Of Kentucky; Navarre, Duroy - Roy; KACHROO, AARDRA - University Of Kentucky; KACHROO, PRADEEP - University Of Kentucky

Submitted to: The Plant Cell
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/17/2012
Publication Date: 4/6/2012
Citation: Mandal, M., Chandra-Shekara, A., Jeong, R., Yu, K., Zhu, S., Chanda, B., Navarre, D.A., Kachroo, A., Kachroo, P. 2012. Oleic acid-dependent modulation of Nitric oxide associated 1 protein levels regulates nitric oxide-mediated defense signaling in Arabidopsis. The Plant Cell. 24:1654-1674.

Interpretive Summary: This work identifies a novel mechanism that regulates plant defense signaling. A fatty acid (oleic acid) is a key regulator of disease physiologies in plants and other organisms. This fatty acid was now found to regulate plant nitric oxide synthesis, and thus nitric oxide signaling. These key insights provide further knowledge of how plants resist disease and ultimately can lead to crops with superior disease resistance, that protect yields and reduce reliance on pesticides.

Technical Abstract: The conserved cellular metabolites nitric oxide (NO) and oleic acid (18:1) are well-known regulators of disease physiologies in diverse organism. We show that NO production in plants is regulated via 18:1. Reduction in 18:1 levels, via a genetic mutation in the 18:1-synthesizing gene SUPPRESSOR OF SA INSENSITIVITY OF npr1-5 (SSI2) or exogenous application of glycerol, induced NO accumulation. Furthermore, both NO application and reduction in 18:1 induced the expression of similar sets of nuclear genes. The altered defense signaling in the ssi2 mutant was partially restored by a mutation in NITRIC OXIDE ASSOCIATED1 (NOA1) and completely restored by double mutations in NOA1 and either of the nitrate reductases. Biochemical studies showed that 18:1 physically bound NOA1, in turn leading to its degradation in a protease-dependent manner. In concurrence, overexpression of NOA1 did not promote NO-derived defense signaling in wild-type plants unless 18:1 levels were lowered. Subcellular localization showed that NOA1 and the 18:1 synthesizing SSI2 proteins were present in close proximity within the nucleoids of chloroplasts. Indeed, pathogen-induced or low-18:1-induced accumulation of NO was primarily detected in the chloroplasts and their nucleoids. Together, these data suggest that 18:1 levels regulate NO synthesis, and, thereby, NO-mediated signaling, by regulating NOA1 levels