| As one of the important plant hormones, jasmonates can regulate plant growth and development in normal conditions; furthermore, as one of the most predominant defense hormones, it is more likely involved in plant defense against pathogen attack, wounding, drought tolerance and other stresses. JASMONATE ZIM-DOMAIN (JAZ) proteins have recently been characterized as repressors in jasmonate signaling, which connect the receptor complex SCFCOIl and the transcriptional factor MYC2. In Arabidopsis thaliana,12JAZ protein encoding genes were identified, but only a few were studied in detail. It’s not clear that how these proteins or genes are involved in JA signaling and its downstream regulation. In this study, we focused on characterizing the molecular networks involving JAZ2and JAZ7. We have isolated T-DNA mutants of JAZ2and JAZ7, jaz2-1and jaz7. With the mutants, we observed their growth phenotypes in the presence or absence of methyl jasmonate (MeJA). To understand the phenotypes and elucidate the regulatory functions of JAZ2and JAZ7, shoot and root tissues from wild type (WT),jaz2and jaz7were harvested for RNA sequencing and metabolomic analysis. In addition, crosstalk between JA and other phytohormones were also discussed. At last, whether overexpression of JAZ7can regulate JA-mediated plant growth and defense were investigated. The results are as follows:1. We studied the gene expression pattern and their phenotypes in the mutants. We found that T-DNA were inserted in the4th intron of JAZ2in jaz2-1with lower expression level and T-DNA were inserted in the promoter region of JAZ7in jaz7, causing the overexpression pattern. MeJA can remarkably inhibit root growth in mutant and WT in a dose-and-time course manner. Under MeJA treatment, there were significant differences in root length as well as fresh weight among genotypes. Specifically, jaz7exhibited shorter root length while jaz2-l has longer root compared to WT. It suggested that JAZ2and JAZ7were positively involved in JA-dependent root length inhibition. Finally, shoot and root tissues were separately harvested for further analysis with10μM Me JA treatment for3weeks.2. Profiles and levels of glucosinolates (GSLs) and mysionase activity were investigated in different tissues among genotypes with or without MeJA. It found out that MeJA can significantly enhance total GSL and aliphatic GSL levels in jaz2-1and WT root tissues. The predominant fold change of GSL was 4-methylsulfinylbutyl GSL (4MSOB). jaz7showed the highest level and4MSOB in jaz2-1was the lowest. In addition, MeJA can induce the production of1-methoxy-3-indolylmethyl GSL (1M0I3M) in jaz2-1and jaz7. Myrosinase activity was remarkably increased in shoot tissues in jaz2-1and WT under MeJA treatment while it was reduced in root tissues; there was no significant change in jaz7.3. Effects of MeJA on transcript reprogramming in Arabidopsis were conducted. With MeJA, the number of transcripts with different expression was most in jaz7, while the number was least in jaz2-1. Moreover, up-regulated transcripts were much more than down-regulated ones. More transcripts with different expression were observed in roots, which even showed significance in jaz7and WT. Among all JAZ genes, except JAZ11and JAZ12, other8genes were up-regulated in all genotypes with MeJA. Expression level of JAZ9was extraordinarily high in all mutants and genotypes after treatment. The fold change of JAZ9expression level was highest in jaz7, and least in jaz2-1. Almost all the genes encoding enzymes in JA biosynthesis were up regulated. In addition, transcription levels of MYC2and JA responsive genes including plant defense genes (PDF1.2, PR3, PR4) and wound responsive genes (VSP, LOX2,Thi2.1) were highly up regulated in all three genotypes. Compared to jaz2-1and WT, more genes involving in metabolic pathways were down regulated in jaz7shoot tissues. Especially, transcripts with different expression levels in shoot were most involved in stress response, small molecular synthesis and secondary metabolism. Down regulated genes with the highest fold change were involved in light stimuli response and photosynthesis. All of the JA-related TFs showed up regulation. jaz7had most these TFs, which mainly took part in stress responses.4. Effects of MeJA on metabolites reprogramming in Arabidopsis were studied. With MeJA, more metabolites were up-regulated in all metabolites with different expression levels, especially in jaz7. Notably,16uniquely induced or suppressed metabolites are diverse in functions, such as antioxidation, defense and protection against cell damage. Among all genotypes, Nδ-acetylornithine showed the highest regulation by MeJA and the level was induced by233.73times in jaz7. Together with transcript changes, both metabolites and genes involved in phenylpropanoid metabolism showed up-regulation. Besides, both structural genes and TFs in glucosinolate metabolism, especially in aliphatic GSL were up-regulated by MeJA.5. Effects of different exogenous hormones on jaz mutants were studied. Only with ABA, jaz7exhibited root inhibition rather than other two genotypes. For hormone determination, the level of auxins, jasmonates as well as GA3were significantly higher with MeJA than those in control. The level fold change of GA3was predominant. It increased by48.83times in jaz7root tissues, which was the most. Genes related to auxins with up regulation were only observed in shoot tissues while genes related to GA3with up regulation were specifically observed in root tissues, which suggested that this pattern related to tissue morphogenesis.6. Plant growth and development, as well as its tolerance to environmental stress were investigated in overexpressed JAZ7plants. In Arabidopsis, jaz7showed less resistance to Sclerotinia sclerotiorum (Lib.) de Bary than WT. However, it exhibited much higher tolerance to drought stress in comparison with WT. Tomato plants with JAZ7overexpression were smaller than WT with curly stems and young leaves. Besides, fruit development was slower in transgenic plants than WT. |
PDF Full Text Request