Abstract
JASMONATE ZIM-DOMAIN (JAZ) proteins are primary transcriptional repressors in the jasmonate (JA) signaling pathway that regulate a broad range of JA-dependent responses. A mechanistic mode of action is well established, but what are the biological roles of individual JAZs, and how do they contribute to the specification of JA signaling outputs? Two recent articles in Journal of Experimental Botany reveal roles of JAZ7 in regulating dark-induced senescence and susceptibility to fungal pathogens. Jasmonates (JAs) regulate a broad range of processes, from growth and development to biotic and abiotic stress responses. JASMONATE ZIM-DOMAIN (JAZ) proteins are key regulators in controlling JA signaling outputs. Since the discovery of JAZs in 2007, over 100 research articles have been published on the characterization of JAZ functions, genomic or transcriptomic analyses of JAZs, or the identification of down-stream transcription factors in the JA signaling pathway through yeast two-hybrid screens using JAZs as bait (reviewed in Pauwels and Goossens, 2011; Shyu and Brutnell, 2015). Biochemical and molecular functions of JAZ proteins have been extensively studied, but surprisingly little is known about the biological role of JAZs and how they contribute to specific JA signaling outputs.
Highlights
JASMONATE ZIM-DOMAIN (JAZ) were identified in 2007 as the missing link between the F-box protein CORONATINE INSENSITIVE 1 (COI1) and the transcription factor MYC2, which mediates JA responses (Chini et al, 2007; Thines et al, 2007; Yan et al, 2007)
JAZ proteins function as transcriptional repressors that repress gene expression by bridging co-repressors NOVEL INTERACTOR OF JAZ (NINJA)/TOPLESS and transcription factors to repress JA-responsive gene expression
In Yu et al (2016), it is shown that jaz7 has a loss-of-function phenotype – something that has only been detected with jaz9 and jaz10 loss-of-function alleles and not with the other 10 JAZ genes to date (Cerrudo et al, 2012; Demianski et al, 2012; Yang et al, 2012; Leone et al, 2014; Yu et al, 2016)
Summary
JASMONATE ZIM-DOMAIN (JAZ) proteins are primary transcriptional repressors in the jasmonate (JA) signaling pathway that regulate a broad range of JA-dependent responses. Upon accumulation of bioactive JA, JAZs form a co-receptor complex with COI1 to perceive JA This interaction leads to ubiquitination and degradation of JAZ proteins, resulting in activation of JAZ-interacting transcription factors and JA-responsive gene expression (reviewed in Pauwels and Goossens, 2011). Screening of multiple jaz T-DNA insertion lines demonstrated that the loss-of-function jaz allele was more sensitive to dark-induced senescence, with enhanced leaf yellowing and reduced chlorophyll content compared to wild type. This phenotype was complemented by 35S::JAZ7 in the jaz background. Overexpression of JAZ7 in the wildtype background showed no significant senescence phenotype, but had reduced H2O2 content compared to wild-type plants These results collectively suggest that JAZ7 plays a role in inhibiting dark-induced senescence. The authors concluded that JAZ7 plays a role in inhibiting dark-induced senescence by controlling senescence, cell death, and defense-responsive gene expression
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