A Maize Jasmonate Zim-Domain Protein, ZmJAZ14, Associates with the JA, ABA, and GA Signaling Pathways in Transgenic Arabidopsis

March A Maize Jasmonate Zim-Domain Protein, ZmJAZ14, Associates with the JA, ABA, and GA Signaling Pathways in Transgenic Arabidopsis Xiaojin Zhou 0 1 Shengwei Yan 0 1 Cheng Sun 0 1 Suzhen Li 0 1 Jie Li 0 1 Miaoyun Xu 0 1 Xiaoqing Liu 0 1 Shaojun Zhang 0 1 Qianqian Zhao 0 1 Ye Li 0 1 Yunliu Fan 0 1 Rumei Chen 0 1 Lei Wang 0 1 0 1 Department of Crop Genomics & Genetic Improvement, Biotechnology Research Institute, Chinese Academy of Agricultural Sciences , Beijing , China , 2 National Key Facility for Crop Gene Resources and Genetic Improvement , Beijing , China , 3 Department of Agronomy, Agricultural University of Hebei/Hebei Sub-center of Chinese National Maize Improvement Center , Baoding , China , 4 College of Life Sciences, Beijing Normal University , Beijing , China 1 Academic Editor: Girdhar K. Pandey, University of Delhi South Campus , INDIA Jasmonate (JA) is an important signaling molecule involved in the regulation of many physiological and stress-related processes in plants. Jasmonate ZIM-domain (JAZ) proteins have been implicated in regulating JA signaling pathways and the cross talk between various phytohormones. Maize is not only an important cereal crop, but also a model plant for monocotyledon studies. Although many JAZ proteins have been characterized in Arabidopsis and rice, few reports have examined the function of JAZ proteins in maize. In this report, we examined the phylogenetic relationship and expression pattern of JAZ family genes in maize. In addition, a tassel and endosperm-specific JAZ gene, ZmJAZ14, was identified using microarray data analysis and real-time RT-PCR, and its expression was induced by polyethylene glycol (PEG), jasmonate (JA), abscisic acid (ABA), and gibberellins (GAs). ZmJAZ14 was shown to be localized in the nucleus and possessed no transcriptional activating activity, suggesting that it functions as a transcriptional regulator. We found that overexpression of ZmJAZ14 in Arabidopsis enhanced plant tolerance to JA and ABA treatment, as well as PEG stress, while it promoted growth under GA stimulus. Moreover, ZmJAZ14 interacted with a subset of transcription factors in Arabidopsis, and the accumulation of several marker genes involved in JA, ABA, and GA signaling pathways were altered in the overexpression lines. These results suggest that ZmJAZ14 may serve as a hub for the cross talk among the JA, ABA, and GA signaling pathways. Our results can be used to further characterize the function of JAZ family proteins in maize, and the gene cloned in this study may serve as a candidate for drought tolerance and growth promotion regulation in maize. - Funding: This work was supported by the National High-Tech R&D Program (grant number 2012AA10A306), the National Key Basic Research Program (Grant No. 2014CB138200) and the National Special Program for Transgenic Research (2014ZX08003-002). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. Plant hormones are implicated in many aspects of plant growth and development, as well as in the response to environmental cues. Both positive and negative regulators are involved in hormonal signal-transduction pathways to mediate various pathways in response to the same stimulus. Therefore, cross talk between various signaling pathways is essential to balance developmental and stress responses. Jasmonates (JAs), a class of fatty acid-derived hormone molecules, are important signaling molecules involved in the regulation of many physiological and stress-related processes in plants, including root growth, senescence, fruit ripening, wounding, water deficit, and pathogen attack [18]. Recently, the underlying mechanism of JA signaling networks during stress responses and development including cooperation between various hormone responses were addressed [9]. Jasmonate ZIM-domain (JAZ) proteins and their interacting partners play essential roles in orchestrating the cross talk between JA and other hormone signaling pathways including gibberellins (GAs), salicylic acid (SA), abscisic acid (ABA), auxin, and ethylene (ET) [7,10,11]. JAZ proteins belong to the TIFY family, which constitutes several plant-specific groups of proteins with various functions [12]. The TIFY family consists of four subgroups including ZML, TIFY, PPD, and JAZ proteins [13]. In the absence of bioactive JA, JAZ proteins repressed the downstream gene expression by physically interacting with members of the R/B-like basic helix-loop-helix (bHLH) transcription factors (TFs), including MYC2, MYC3, and MCY4 [14 16]. In response to stress, such as insect feeding or pathogen infection, the level of bioactive JA increases. An F-box protein CORONATINE INSENSITIVE1 (COI1) perceives JA signals and recruits JAZ proteins for ubiquitin-mediated protein degradation. As a result, R/B-like bHLH TFs are released from JAZ proteins, and the downstream genes required for JA-mediated responses are activated [17,18]. Furthermore, the function of several co-regulators of JAZ proteins were identified, such as Novel Interactor of JAZ (NINJA), TOPLESS proteins (TPL), ethylene-stabilized TFs (EIN3/EIL1), R2R3-MYB TFs (MYB21/MYB24), and DELLA proteins [19]. The NINJA protein was identified using a tandem affinity purification method, and NINJA was co-purified with TPL and the related protein TPR, which has been implicated in the regulation of auxin signaling pathways [20,21]. EIN3 and EIL1 are TFs that respond to ethylene and activate a subset of genes involved in pathogen defense and developmental regulation [22]. The activity of EIN3 and EIL1 can be regulated by JA through binding with JAZ proteins [23], indicating that JAZ degradation by JA signaling is required for full activation of these TFs. The R2R3 MYB-type TFs, MYB21 and MYB24, have also been identified as JAZ-interacting proteins [24]. The myb21 mutant showed reduced fertility, and myb24 exacerbated this phenotype, while overexpression of MYB21 partially restores the sterility phenotype of coi1 [24,25]. These results suggested that MYB21 and MYB24 may be implicated in JA-mediated male fertility. DELLA proteins function as essential regulators of GA signaling, and they are responsible for repressing the expression of GA-induced genes in the absence of hormone [26]. Repressor of gal-3 (RGA), a DELLA protein, was identified as a JAZ1 binding protein, and further analysis revealed that RGA and MYC2 compete for binding to JAZ1, indicating that DELLA may diminish the interaction between JAZ and MYC2 and thus relieve JAZ repression of JA-inducible genes [27]. These studies indicate that JAZ proteins may serve as transcriptional repressors in JA signaling pathways and act as hubs in an extensive signaling network, influencing various hormone pathways and aspects of plant growth. Characterizing hormonal cross talk is essential to understand how (...truncated)