Abstract
Powdery mildew, caused by the biotrophic fungal pathogen Blumeria graminis f. sp. tritici, is a major limitation for wheat yield. However, the molecular mechanisms underlying wheat resistance against powdery mildew remain largely unclear. In this study, we report the role of JASMONATE-ZIM domain protein TaJAZ1 in regulating bread wheat resistance against powdery mildew. We generated transgenic bread wheat lines over-expressing the truncated TaJAZ1 without the Jas motif, which showed increased TaPR1/2 gene expression and reactive oxygen species accumulation, leading to enhanced resistance against powdery mildew. Simultaneously, we identified a Jasmonic acid (JA)-induced bHLH transcription factor TaMYC4 in bread wheat. We demonstrated that TaJAZ1 directly interacts with TaMYC4 to repress its transcriptional activity. Meanwhile, we show that the ZIM domain of TaJAZ1 interacts with the C terminus of TaNINJA, whereas the N-terminal EAR motif of TaNINJA interacts with the transcriptional co-repressor TaTPL. Collectively, our work pinpoints TaJAZ1 as a favorable gene to enhance bread wheat resistance toward powdery mildew, and provides a molecular framework for JA signaling in bread wheat.
Highlights
Bread wheat (Triticum aestivum; 2n = 42; AABBDD) is a major staple crop worldwide
Major discoveries in the model plant Arabidopsis thaliana have revealed a core Jasmonic acid (JA) signaling framework consisting of an F-box protein CORONATIN INSENSITIVE 1 (COI1), which forms the functional Skp-Cullin-F-box (SCF) E3 ubiquitin ligase complex SCFCOI1 with Cullin[1] and Arabidopsis Skp1-like protein ASK114–16; a basic helix-loop-helix transcription factor (TF) MYC2 that acts as a master regulator in JA signaling pathway[17,18,19]; Jasmonate-ZIM domain (JAZ) proteins directly interact with MYC2 and repress its transcriptional activity[20,21,22]; JAZs that recruit the TOPLESS (TPL) co-repressor, either directly or through the NOVEL INTERACTOR OF JAZ (NINJA) adapter protein, which epigenetically inhibits expression of TF target genes[21]
Wang et al (2017) identified fourteen JAZ genes in wheat based on the wheat genome data, and confirmed that some of these JAZ genes were transcriptionally affected by multifarious abiotic stress treatments and phytohormone[41]
Summary
To improve bread wheat resistance against powdery mildew, it is useful to identify the key regulators for bread wheat defense responses. A previous study reported that simultaneous editing of all three TaMLO homoeologous in bread wheat confers heritable broad-spectrum resistance to powdery mildew[2]. It has been demonstrated that OsMYC2 interacted with some OsJAZ proteins and regulated the expression of early JA-responsive genes to influence the bacterial blight resistance in rice[27]. We demonstrated that the transgenic bread wheat lines over-expressing the truncated TaJAZ1 protein lacking the Jas motif displayed increased TaPR1/2 gene expression and reactive oxygen species (ROS) accumulation, leading to enhanced resistance against powdery mildew. Our work demonstrates that TaJAZ1 positively regulates bread wheat resistance against powdery mildew, and provides a molecular framework for JA signaling in bread wheat
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