Possible Involvement of MYB44-Mediated Stomatal Regulation in Systemic Resistance Induced by Penicillium simplicissimum GP17-2 in Arabidopsis

MYB44 regulates PTI by promoting the expression of EIN2 and MPK3/6 in Arabidopsis

The plant signaling pathway that regulates pathogen-associated molecular pattern (PAMP)-triggered immunity (PTI) involves mitogen-activated protein kinase (MAPK) cascades that comprise sequential activation of several protein kinases and the ensuing phosphorylation of MAPKs, which activate transcription factors (TFs) to promote downstream defense responses. To identify plant TFs that regulate MAPKs, we investigated TF-defective mutants of Arabidopsis thaliana and identified MYB44 as an essential constituent of the PTI pathway. MYB44 confers resistance against the bacterial pathogen Pseudomonas syringae by cooperating with MPK3 and MPK6. Under PAMP treatment, MYB44 binds to the promoters of MPK3 and MPK6 to activate their expression, leading to phosphorylation of MPK3 and MPK6 proteins. In turn, phosphorylated MPK3 and MPK6 phosphorylate MYB44 in a functionally redundant manner, thus enabling MYB44 to activate MPK3 and MPK6 expression and further activate downstream defense responses. Activation of defense responses has also been attributed to activation of EIN2 transcription by MYB44, which has previously been shown to affect PAMP recognition and PTI development. AtMYB44 thus functions as an integral component of the PTI pathway by connecting transcriptional and posttranscriptional regulation of the MPK3/6 cascade.

Alterations in Sucrose and Phenylpropanoid Metabolism Affected by BABA-Primed Defense in Postharvest Grapes and the Associated Transcriptional Mechanism

Defense elicitors can induce fruit disease resistance to control postharvest decay but may incur quality impairment. Our present work aimed to investigate the resistance against Botrytis cinerea induced by the elicitor β-aminobutyric acid (BABA) and to elucidate the specific transcriptional mechanism implicated in defense-related metabolic regulations. The functional dissection results demonstrated that, after inoculation with the fungal necrotroph B. cinerea, a suite of critical genes encoding enzymes related to the sucrose metabolism and phenylpropanoid pathway in priming defense in grapes were transcriptionally induced by treatment with 10 mM BABA. In contrast, more UDP-glucose, a shared precursor of phenylpropanoid and sucrose metabolism, may be redirected to the phenylpropanoid pathway for the synthesis of phytoalexins, including trans-resveratrol and ɛ-viniferin, in 100 mM BABA-treated grapes, resulting in direct resistance but compromised soluble sugar contents. An R2R3-type MYB protein from Vitis vinifera, VvMYB44, was isolated and characterized. VvMYB44 expression was significantly induced upon the grapes expressed defensive reaction. Subcellular localization, yeast two-hybrid, and coimmunoprecipitation assays revealed that the nuclear-localized VvMYB44 physically interacted with the salicylic acid-responsive transcription coactivator NPR1 in vivo for defense expression. In addition, VvMYB44 directly bound to the promoter regions of sucrose and phenylpropanoid metabolism-related genes and transactivated their expression, thus tipping the balance of antifungal compound accumulation and soluble sugar maintenance. Hence, these results suggest that 2R-type VvMYB44 might be a potential positive participant in BABA-induced priming defense in grape berries that contributes to avoiding the excessive consumption of soluble sugars during the postharvest storage.[Formula: see text] Copyright © 2021 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Identification and mapping of CpPM10.1, a major gene involved in powdery mildew (race 2 France of Podosphaera xanthii) resistance in zucchini (Cucurbita pepo L.)

Powdery mildew resistance in zucchini is controlled by one major dominant locus, CpPM10.1. CpPM10.1 was fine mapped. The expression of candidate gene Cp4.1LG10g02780 in resistant individuals was significantly upregulated after inoculation with the powdery mildew. Powdery mildew (PM) is one of the most destructive fungal diseases, reducing the productivity of Cucurbita crops globally. PM influences the photosynthesis, growth and development of infected zucchini and seriously reduces fruit yield and quality. In the present study, the zucchini inbred line 'X10' had highly stable PM resistance, and the inbred line 'Jin234' was highly susceptible to PM in the seedling stage and adult stages. Genetic analysis revealed that PM resistance in 'X10' is controlled by one major dominant locus. Based on the strategy of QTL-seq combined with linkage analysis and developed molecular markers, the major locus was found to be located in a 382.9-kb candidate region on chromosome 10; therefore, the major locus was named CpPM10.1. Using 1,400 F₂ individuals derived from a cross between 'X10' and 'JIN234' and F_2:3 offspring of the recombinants, the CpPM10.1 locus was defined in a region of approximately 20.9 kb that contained 5 coding genes. Among them, Cp4.1LG10g02780 contained a conserved domain (RPW8), which controls resistance to a broad range of PM pathogens. Cp4.1LG10g02780 also had nonsynonymous SNPs between the resistant 'X10' and susceptible 'Jin234.' Furthermore, the expression of Cp4.1LG10g02780 was strongly positively involved in PM resistance in the key period of inoculation. Further allelic diversity analysis in zucchini germplasm resources indicated that PM resistance was associated with two SNPs in the Cp4.1LG10g02780 RPW8 domain. This study not only provides highly stable PM resistance gene resources for cucurbit crops but also lays the foundation for the functional analysis of PM resistance and resistance breeding in zucchini.

Comparative Transcriptomic Analysis of Biological Process and Key Pathway in Three Cotton (Gossypium spp.) Species Under Drought Stress

Drought is one of the most important abiotic stresses that seriously affects cotton growth, development, and production worldwide. However, the molecular mechanism, key pathway, and responsible genes for drought tolerance incotton have not been stated clearly. In this research, high-throughput next generation sequencing technique was utilized to investigate gene expression profiles of three cotton species (Gossypium hirsutum, Gossypium arboreum, and Gossypium barbadense L.) under drought stress. A total of 6968 differentially expressed genes (DEGs) were identified, where 2053, 742, and 4173 genes were tested as statistically significant; 648, 320, and 1998 genes were up-regulated, and 1405, 422, and 2175 were down-regulated in TM-1, Zhongmian-16, and Pima4-S, respectively. Total DEGs were annotated and classified into functional groups under gene ontology analysis. The biological process was present only in tolerant species(TM-1), indicating drought tolerance condition. The Kyoto encyclopedia of genes and genomes showed the involvement of plant hormone signal transduction and metabolic pathways enrichment under drought stress. Several transcription factors associated with ethylene-responsive genes (ICE1, MYB44, FAMA, etc.) were identified as playing key roles in acclimatizing to drought stress. Drought also caused significant changes in the expression of certain functional genes linked to abscisic acid (ABA) responses (NCED, PYL, PP2C, and SRK2E), reactive oxygen species (ROS) related in small heat shock protein and 18.1 kDa I heat shock protein, YLS3, and ODORANT1 genes. These results will provide deeper insights into the molecular mechanisms of drought stress adaptation in cotton.

Engineering d-limonene synthase down-regulation in orange fruit induces resistance against the fungus Phyllosticta citricarpa through enhanced accumulation of monoterpene alcohols and activation of defence

Terpene volatiles play an important role in the interactions between specialized pathogens and fruits. Citrus black spot (CBS), caused by the fungus Phyllosticta citricarpa, is associated with crop losses in different citrus-growing areas worldwide. The pathogen may infect the fruit for 20-24 weeks after petal fall, but the typical hard spot symptoms appear when the fruit have almost reached maturity, caused by fungal colonization and the induction of cell lysis around essential oil cavities. d-Limonene represents approximately 95% of the total oil gland content in mature orange fruit. Herein, we investigated whether orange fruit with reduced d-limonene content in peel oil glands via an antisense (AS) approach may affect fruit interaction with P. citricarpa relative to empty vector (EV) controls. AS fruit showed enhanced resistance to the fungus relative to EV fruit. Because of the reduced d-limonene content, an over-accumulation of linalool and other monoterpene alcohols was found in AS relative to EV fruit. A global gene expression analysis at 2 h and 8 days after inoculation with P. citricarpa revealed the activation of defence responses in AS fruit via the up-regulation of different pathogenesis-related (PR) protein genes, probably as a result of enhanced constitutive accumulation of linalool and other alcohols. When assayed in vitro and in vivo, monoterpene alcohols at the concentrations present in AS fruit showed strong antifungal activity. We show here that terpene engineering in fruit peels could be a promising method for the development of new strategies to obtain resistance to fruit diseases.

The AtMYB44 promoter is accessible to signals that induce different chromatin modifications for gene transcription

AtMYB44 transcripts accumulate non-specifically under diverse stress conditions and with various phytohormone treatments in Arabidopsis thaliana. We investigated the chromatin modifications caused by various signals to uncover the induction mechanism of AtMYB44 transcription. Bisulfite sequencing confirmed a previous database illustrating that the AtMYB44 promoter and gene-body regions are completely DNA methylation-free. Chromatin immunoprecipitation (ChIP) assays revealed that the nucleosome density is remarkably low at the AtMYB44 promoter region. Thus, the promoter region appears to be highly accessible for various trans-acting factors. ChIP assays revealed that osmotic stress (mannitol treatment) lowered the nucleosome density at the gene-body regions, while abscisic acid (ABA) or jasmonic acid (JA) treatment did so at the proximal transcription start site (TSS) region. In response to mannitol treatment, histone H3 lysine 4 trimethylation (H3K4me3) and H3 acetylation (H3ac) levels within the promoter, TSS, and gene-body regions of AtMYB44 were significantly increased. However, occupancy of histone variant H2A.Z was not affected by the mannitol treatment. We previously reported that salt stress triggered a significant decrease in H2A.Z occupation without affecting the H3K4me3 and H3ac levels. In combination, our data suggest that each signal transduced to the highly accessible promoter induces a different chromatin modification for AtMYB44 transcription.

Comparative transcriptome analysis of two citrus germplasms with contrasting susceptibility to Phytophthora nicotianae provides new insights into tolerance mechanisms

Host perception of Phytophthora nicotianae switching to necrotrophy is fundamental for disease tolerance of citrus. It involves an HR-like response, strengthening of the cell wall structure and hormonal signaling. Stem rot caused by P. nicotianae is a worldwide disease of several important crops, including citrus. Given the growing awareness of chemical fungicides drawbacks, genetic improvement of citrus rootstocks remains the best alternative. However, the molecular basis underlying the successful response of resistant and/or tolerant genotypes remains poorly understood. Therefore, we performed a transcriptomic analysis to examine the differential defense response to P. nicotianae of two germplasms-tolerant sour orange (SO, Citrus aurantium) and susceptible Madam Vinous (MV, C. sinensis)-in both the biotrophic and necrotrophic phases of host-pathogen interaction. Our results revealed the necrotrophic phase as a decisive turning point, since it included stronger modulation of a number of genes implicated in pathogen perception, signal transduction, HR-like response, transcriptional reprogramming, hormone signaling, and cell wall modifications. In particular, the pathogen perception category reflected the ability of SO to perceive the pathogen even after its switch to necrotrophy, and thus to cope successfully with the infection, while MV failed. The concomitant changes in genes involved in the remaining functional categories seemed to prevent pathogen spread. This investigation provided further understanding of the successful defense mechanisms of C. aurantium against P. nicotianae, which might be exploited in post-genomic strategies to develop resistant Citrus genotypes.