JAV1 Controls Jasmonate-Regulated Plant Defense

Abstract

Plants evolve effective mechanisms to protect themselves from environmental stresses and employ jasmonates as vital defense signals to defend against insect attack and pathogen infection. Jasmonates are also recognized as an essential growth regulator by which diverse developmental processes are mediated. Despite substantial research, there are no key signaling components reported yet to control jasmonate-regulated plant defense independent of developmental responses. We identify JAV1, a key gene in the jasmonate pathway, which functions as a negative regulator to control plant defense but does not play a detectable role in plant development. Our results suggest that when encountering insect attack and pathogen infection, plants accumulate jasmonates that trigger JAV1 degradation via the 26S proteasome to activate defensive gene expression and elevate resistances against both insects and pathogens. These findings have provided insight into the molecular mechanism by which plants integrate jasmonate signals to protect themselves from insect attack and pathogen infection.

The VQ Motif-Containing Protein Family of Plant-Specific Transcriptional Regulators

“…A transient expression assay using Arabidopsis mesophyll protoplasts reveals that, except for VQ1, VQ10, VQ22, VQ25, and VQ27, all members of the Arabidopsis VQ family facilitate either transcriptional activation or repression (Li et al, 2014), likely through the binding of specific transcription factors to cis-elements or other coregulators. In agreement with this, genome-wide profiling demonstrated that VQ21 and VQ22 regulate numerous defenseresponsive genes in the SA-and JA-mediated signaling pathway, respectively (Andreasson et al, 2005;Hu et al, 2013a). This notion is further supported by the nuclear localization of some VQ proteins fused with GFP.…”

“…Wounding also triggered the degradation of VQ22 in the wild type but not in coronatine insensitive1 (coi1) mutant plants. These results demonstrate that jasmonate or wounding triggers the degradation of VQ22 via the 26S proteasome pathway in a COI1-dependent manner (Hu et al, 2013a). The degradation of VQ22 upon insect attack or pathogen infection likely releases its inhibitory role on positive effectors of plant defense responses (such as WRKY transcription factors).…”

“…Silencing of VQ22 enhanced resistance to necrotrophic pathogens and herbivorous insects, whereas transgenic lines constitutively expressing VQ22 were highly susceptible to these biotic stresses (Hu et al, 2013a), indicating that VQ22 functions as a negative regulator of JA-mediated plant defense. Therefore, members of the VQ family play either positive or negative roles in SA-and/or JA-mediated plant immune responses, possibly by interacting with different WRKY transcription factors and mediating distinct activities (see below).…”

“…3C; Wang et al, 2010). In addition, VQ22 may interact with WRKY28 and WRKY51 to negatively control JA-mediated defense (Hu et al, 2013a). Two systematic yeast two-hybrid assays showed that a large proportion of VQ proteins associate physically with members of group I or group IIc WRKY transcription factors (Table I; Rushton et al, 2010;Cheng et al, 2012;Pecher et al, 2014).…”

“…For instance, B. cinerea infection and SA treatment rapidly and strongly induce VQ23 and VQ16 transcript levels (Narusaka et al, 2008;Xie et al, 2010;Lai et al, 2011). VQ22 transcript is significantly increased upon JA treatment and quickly accumulates after mechanical wounding (Hu et al, 2013a). Moreover, VQ15 is induced in seedlings exposed to various abiotic stresses, including dehydration, low temperature, or high salinity, while VQ9 expression is increased by NaCl stress treatment (Perruc et al, 2004;Hu et al, 2013b).…”