Abstract
Hevea brasiliensis Müll. Arg. is one of the most frequently wounded plants worldwide. Expelling latex upon mechanical injury is a wound response of rubber trees. However, JA-mediated wound responses in rubber trees are not well documented. In this work, three JAZ-interacting MYC transcription factors of H. brasiliensis (termed HbMYC2/3/4) were identified by yeast two-hybrid screening. HbMYC2/3/4 each showed specific interaction profiles with HbJAZs. HbMYC2/3/4 each localized in the nucleus and exhibited strong transcriptional activity. To identify the target genes potentially regulated by HbMYC2/3/4, cis-elements interacting with HbMYC2/3/4 were first screened by yeast one-hybrid assays; the results indicated that HbMYC2/3/4 each could bind G-box elements. Additional analysis confirmed that HbMYC2/3/4 bound the HbPIP2;1 promoter, which contains five G-box cis-elements, and regulated the expression of reporter genes in yeast cells and in planta. HbMYC2/3/4 were induced by exogenous JA treatment but suppressed by ethylene (ET) treatment; in contrast, HbPIP2;1 was positively regulated by ET but negatively regulated by JA treatment. Given that HbPIP2;1 is involved in latex drainage, it could be proposed that HbMYC2/3/4 are involved in the regulation of HbPIP2;1 expression as well as latex drainage, both of which are coordinated by the JA and ET signalling pathways.
Highlights
As the SCFCOI1 complex is highly conserved in plants[13,17,18], the spatially and temporally specific expression and alternative splicing as well as the differing repression of target transcription factors of individual jasmonate ZIM-domain (JAZ) gene members may account for the specific responses of plants to jasmonic acid (JA) signals[17,19]
To screen the JAZ-interacting transcription factors in H. brasiliensis, the full-length ORFs of HbJAZ1 were inserted into pGBKT7 and transformed into a Y2HGold strain to generate a bait reporter strain
Four prey proteins were identified as putative transcription factors, including three basic helix-loop-helix transcription factors and one zinc-finger protein
Summary
Over 2,000 plant species produce rubber (cis-1–4-polyisoprene). Because of its high rubber productivity and rubber quality, Hevea brasiliensis Müll. Previous reports have shown that mechanical wounding induces laticifer differentiation and latex production. The induction of laticifers could serve as an excellent indicator of the wounding response and latex biosynthesis regulated by JA in rubber trees. JAZ proteins function as repressors of JA signalling to interact with JA-responsive transcription factors (e.g., MYC2) and inhibit their transcription[14,16]. After the perception of wounding signals or developmental cues, JA accumulates and is conjugated with isoleucine, which serves as active form to mediate the interaction between COI1 and JAZ repressors, leading to the ubiquitination of JAZ proteins. The key step to reveal the JA signalling pathway in H. brasiliensis is the identification of transcription factors regulated by JAZ proteins. The data provided in this study might fill the gaps of the JA-mediated mechanism of latex biosynthesis and drainage in rubber trees
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