Arabidopsis VQ18 and VQ26 proteins interact with ABI5 transcription factor to negatively modulate ABA response during seed germination

Abstract

Seed germination and early seedling establishment, critical developmental stages in the life cycle of seed plants, are modulated by diverse endogenous hormones and the surrounding environment. Arabidopsis ABSCISIC ACID-INSENSITIVE5 (ABI5) is a central transcription factor of abscisic acid (ABA) signaling that represses those processes. ABI5 is precisely modulated at post-translational level; however, whether it interacts with other crucial transcriptional regulators remains to be investigated. In this study, VQ18 and VQ26, two members of the recently-identified VQ family, were found to interact with ABI5 in vitro and in vivo. Phenotypic analysis showed that VQ18 and VQ26 are responsive to ABA and negatively mediate ABA signaling redundantly during seed germination. Simultaneously decreasing VQ18 and VQ26 expression levels enhanced ABA signaling to suppress seed germination, whereas overexpressing these two VQ genes resulted in the germinated seeds being less ABA-sensitive. Consistently, the expression levels of several ABI5 targets were modulated by VQ18 and VQ26. The increased ABA signaling of plants in which VQ18 and VQ26 were simultaneously suppressed required ABI5. Additionally, VQ18 and VQ26 acted as negative interactors of the ABI5 transcription factor. Our study reveals a previously unidentified regulatory role of VQ proteins, which act antagonistically with ABI5 to maintain the appropriate ABA signaling level to fine-tune seed germination and early seedling establishment.

Molecular Mechanism Underlying the Synergetic Effect of Jasmonate on Abscisic Acid Signaling during Seed Germination in Arabidopsis

“…In a recent study (Pan et al, 2018), two VQ (containing the conserved FxxxVQxxTG motif) proteins, VQ18 and VQ26, were shown to physically associate with ABI5 and interfere with its transcriptional role.…”

“…To generate JAZ-and ABI3-OE transgenic lines, the full-length cDNA of ABI3 was cloned into the binary vector pOCA30 (Pan et al, 2018) in the sense orientation behind the CaMV 35S promoter (Hu et al, 2013).…”

“…The Co-IP assays were performed as described elsewhere (Pan et al, 2018). Briefly, the full-length CDSs of JAZ1 and JAZ5 were separately cloned into a tagging vector with HA-tag in the sense orientation downstream of the CaMV 35S promoter.…”

“…Briefly, the full-length CDSs of JAZ1 and JAZ5 were separately cloned into a tagging vector with HA-tag in the sense orientation downstream of the CaMV 35S promoter. ABI3 was fused to a 3×MYC-tag to form the ABI3-3MYC fusion protein (Pan et al, 2018). The fusion proteins were transiently coexpressed in N. benthamiana leaves.…”

Genome-Wide Identification of the VQ Protein Gene Family of Tobacco (Nicotiana tabacum L.) and Analysis of Its Expression in Response to Phytohormones and Abiotic and Biotic Stresses

“…tomato in transgenic Petunia plants [32][33][34]; jasmonate-associated VQ motif protein 1 (JAV1, also known as AtVQ22) acts as a repressor protein in JA-mediated defense responses against necrotrophic pathogens and herbivorous insects without influencing plant growth and development [35,36]; SIB1/AtVQ23 and SIB2/AtVQ16 function as activators in plant defense against necrotrophic pathogens [37]. Additionally, AtVQ18 and AtVQ26 were found to fine-tune seed germination and seedling establishment [38], while AtVQ29 was reported to interact with Phytochrome-Interacting Factor 1 (PIF1), leading to the repression of seedling de-etiolation [39]. The banana fruit VQ5 acts as a repressor of cold-responsive transcription factor MaWRKY26 involved in activating JA biosynthesis [25].…”