AtMYB44 regulates resistance to the green peach aphid and diamondback moth by activating EIN2-affected defences in Arabidopsis

Appropriate induction of TOC1 ensures optimal MYB44 expression in ABA signaling and stress response in Arabidopsis

Plants possess the remarkable ability to integrate the circadian clock with various signalling pathways, enabling them to quickly detect and react to both external and internal stress signals. However, the interplay between the circadian clock and biological processes in orchestrating responses to environmental stresses remains poorly understood. TOC1, a core component of the plant circadian clock, plays a vital role in maintaining circadian rhythmicity and participating in plant defences. Here, our study reveals a direct interaction between TOC1 and the promoter region of MYB44, a key gene involved in plant defence. TOC1 rhythmically represses MYB44 expression, thereby ensuring elevated MYB44 expression at dawn to help the plant in coping with lowest temperatures during diurnal cycles. Additionally, both TOC1 and MYB44 can be induced by cold stress in an Abscisic acid (ABA)-dependent and independent manner. TOC1 demonstrates a rapid induction in response to lower temperatures compared to ABA treatment, suggesting timely flexible regulation of TOC1-MYB44 regulatory module by the circadian clock in ensuring a proper response to diverse stresses and maintaining a balance between normal physiological processes and energy-consuming stress responses. Our study elucidates the role of TOC1 in effectively modulating expression of MYB44, providing insights into the regulatory network connecting the circadian clock, ABA signalling, and stress-responsive genes.

Transcriptome analysis reveals the potential mechanism of the response to scale insects in Camellia sasanqua Thunb

BACKGROUND

Camellia sasanqua Thunb. is an essential woody ornamental plant. Our continuous observation found that scale insects often infest C. sasanqua all year round in Kunming, China, resulting in poor growth. Scientifically preventing and controlling the infestation of scale insects should be paid attention to, and the mechanism of scale insects influencing C. sasanqua should be used as the research basis.

RESULTS

The scale insect was identified as Pseudaulacaspis sasakawai Takagi. We analyzed transcriptome sequencing data from leaves of C. sasanqua infested with scale insects. A total of 1320 genes were either up-regulated or down-regulated and differed significantly in response to scale insects. GO (Gene Ontology) annotation analysis showed that the pathway of catalytic activity, binding, membrane part, cell part, and cellular process were affected. KEGG (Kyoto Encyclopedia of Genes and Genomes) pathway analysis showed that most DEGs (differentially expressed genes) involved in plant hormone signal transduction, MAPK signaling pathway, flavonoid biosynthesis, tropane, piperidine and pyridine alkaloid biosynthesis. We also observed that the expression of galactose metabolism and carotenoid biosynthesis were significantly influenced. In addition, qRT-PCR (quantitative real-time PCR) validated the expression patterns of DEGs, which showed an excellent agreement with the transcriptome sequencing.

CONCLUSIONS

Our transcriptomic analysis revealed that the C. sasanqua had an intricate resistance strategy to cope with scale insect attacks. After sensing the attack signal of scale insects, C. sasanqua activated the early signal MAPK (mitogen-activated protein kinase) to activate further transcription factors and Auxin, ET, JA, ABA, and other plant hormone signaling pathways, ultimately leading to the accumulation of lignin, scopolin, flavonoids and other secondary metabolites, produces direct and indirect resistance to scale insects. Our results suggested that it provided some potential resources of defense genes that would benefit the following resistance breeding in C. sasanqua to scale insects.

Genome-Wide Analysis of MYB Genes in Primulina eburnea (Hance) and Identification of Members in Response to Drought Stress

Due to periodic water deficiency in karst environments, Primulina eburnea experiences sporadic drought stress in its habitat. Despite being one of the largest gene families and functionally diverse in terms of plant growth and development, MYB transcription factors in P. eburnea have not been studied. Here, a total of 230 MYB genes were identified in P. eburnea, including 67 1R-MYB, 155 R2R3-MYB, six 3R-MYB, and two 4R-MYB genes. The R2R3-type PebMYB genes could be classified into 16 subgroups, while the remaining PebMYB genes (1R-MYB, 3R-MYB, and 4R-MYB genes) were divided into 10 subgroups. Notably, the results of the phylogenetic analysis were further supported by the motif and gene structure analysis, which showed that individuals in the same subgroup had comparable motif and structure organization. Additionally, gene duplication and synteny analyses were performed to better understand the evolution of PebMYB genes, and 291 pairs of segmental duplicated genes were found. Moreover, RNA-seq analysis revealed that the PebMYB genes could be divided into five groups based on their expression characteristics. Furthermore, 11 PebMYB genes that may be involved in drought stress response were identified through comparative analysis with Arabidopsis thaliana. Notably, seven of these genes (PebMYB3, PebMYB13, PebMYB17, PebMYB51, PebMYB142, PebMYB69, and PebMYB95) exhibited significant differences in expression between the control and drought stress treatments, suggesting that they may play important roles in drought stress response. These findings clarified the characteristics of the MYB gene family in P. eburnea, augmenting our comprehension of their potential roles in drought stress adaptation.

A novel transcriptional repressor complex MYB22-TOPLESS-HDAC1 promotes rice resistance to brown planthopper by repressing F3'H expression

The brown planthopper (BPH) is the most destructive pest of rice. The MYB transcription factors are vital for rice immunity, but most are activators. Although MYB22 positively regulates rice resistance to BPH and has an EAR motif associated with active repression, it remains unclear whether it is a transcriptional repressor affecting rice-BPH interaction. Genetic analyses revealed that MYB22 regulates rice resistance to BPH via its EAR motif. Several biochemical experiments (e.g. transient transcription assay, Y2H, LCA, and BiFC) indicated that MYB22 is a transcriptional repressor that interacts with the corepressor TOPLESS via its EAR motif and recruits HDAC1 to form a tripartite complex. Flavonoid-3'-hydroxylase (F3'H) is a flavonoid biosynthesis pathway-related gene that negatively regulates rice resistance to BPH. Based on a bioinformatics analysis and the results of EMSA and transient transcription assays, MYB22 can bind directly to the F3'H promoter and repress gene expression along with TOPLESS and HDAC1. We revealed a transcriptional regulatory mechanism influencing the rice-BPH interaction that differs from previously reported mechanisms. Specifically, MYB22-TOPLESS-HDAC1 is a novel transcriptional repressor complex with components that synergistically and positively regulate rice resistance to BPH through the transcriptional repression of F3'H.

The pivotal role of MYB transcription factors in plant disease resistance

MAIN CONCLUSION

MYB transcription factors are essential for diverse biology processes in plants. This review has focused on the potential molecular actions of MYB transcription factors in plant immunity. Plants possess a variety of molecules to defend against disease. Transcription factors (TFs) serve as gene connections in the regulatory networks controlling plant growth and defense against various stressors. As one of the largest TF families in plants, MYB TFs coordinate molecular players that modulate plant defense resistance. However, the molecular action of MYB TFs in plant disease resistance lacks a systematic analysis and summary. Here, we describe the structure and function of the MYB family in the plant immune response. Functional characterization revealed that MYB TFs often function either as positive or negative modulators towards different biotic stressors. Moreover, the MYB TF resistance mechanisms are diverse. The potential molecular actions of MYB TFs are being analyzed to uncover functions by controlling the expression of resistance genes, lignin/flavonoids/cuticular wax biosynthesis, polysaccharide signaling, hormone defense signaling, and the hypersensitivity response. MYB TFs have a variety of regulatory modes that fulfill pivotal roles in plant immunity. MYB TFs regulate the expression of multiple defense genes and are, therefore, important for increasing plant disease resistance and promoting agricultural production.

Importin β1 Mediates Nuclear Entry of EIN2C to Confer the Phloem-Based Defense against Aphids

Ethylene Insensitive 2 (EIN2) is an integral membrane protein that regulates ethylene signaling towards plant development and immunity by release of its carboxy-terminal functional portion (EIN2C) into the nucleus. The present study elucidates that the nuclear trafficking of EIN2C is induced by importin β1, which triggers the phloem-based defense (PBD) against aphid infestations in Arabidopsis. In plants, IMPβ1 interacts with EIN2C to facilitate EIN2C trafficking into the nucleus, either by ethylene treatment or by green peach aphid infestation, to confer EIN2-dependent PBD responses, which, in turn, impede the phloem-feeding activity and massive infestation by the aphid. In Arabidopsis, moreover, constitutively expressed EIN2C can complement the impβ1 mutant regarding EIN2C localization to the plant nucleus and the subsequent PBD development in the concomitant presence of IMPβ1 and ethylene. As a result, the phloem-feeding activity and massive infestation by green peach aphid were highly inhibited, indicating the potential value of EIN2C in protecting plants from insect attacks.

OsPPR11 encoding P-type PPR protein that affects group II intron splicing and chloroplast development

OsPPR11 belongs to the P-type PPR protein family and can interact with OsCAF2 to regulate Group II intron splicing and affect chloroplast development in rice. Pentatricopeptide repeat (PPR) proteins participate in chloroplasts or mitochondria group II introns splicing in plants. The PPR protein family contains 491 members in rice, but most of their functions are unknown. In this study, we identified a nuclear gene encoding the P-type PPR protein OsPPR11 in chloroplasts. The qRT-PCR analysis demonstrated that OsPPR11 was expressed in all plant tissues, but leaves had the highest expression. The osppr11 mutants had yellowing leaves and a lethal phenotype that inhibited chloroplast development and photosynthesis-related gene expression and reduced photosynthesis-related protein accumulation in seedlings. Moreover, photosynthetic complex accumulation decreased significantly in osppr11 mutants. The OsPPR11 is required for ndhA, and ycf3-1 introns splicing and interact with CRM family protein OsCAF2, suggesting that these two proteins may form splicing complexes to regulate group II introns splicing. Further analysis revealed that OsCAF2 interacts with OsPPR11 through the N-terminus. These results indicate that OsPPR11 is essential for chloroplast development and function by affecting group II intron splicing in rice.

Identification of Peanut AhMYB44 Transcription Factors and Their Multiple Roles in Drought Stress Responses

MYB transcription factors (TFs) comprise a large gene family that plays an important role in plant growth, development, stress responses, and defense regulation. However, their functions in peanut remain to be further elucidated. Here, we identified six AhMYB44 genes (AhMYB44-01/11, AhMYB44-05/15, and AhMYB44-06/16) in cultivated peanut. They are typical R2R3-MYB TFs and have many similarities but different expression patterns in response to drought stress, suggesting different functions under drought stress. Homologous genes with higher expression in each pair were selected for further study. All of them were nuclear proteins and had no self-transactivation activity. In addition, we compared the performances of different lines at germination, seedling, and adult stages under drought stress. After drought treatment, the overexpression of AhMYB44-11 transgenic plants resulted in the longest root length at the seedling stage. Levels of proline, soluble sugar and chlorophyll, and expression levels of stress-related genes, including P5CS1, RD29A, CBF1, and COR15A, were higher than those of the wild type (WT) at the adult stage. While the overexpression of AhMYB44-16 significantly increased the drought sensitivity of plants at all stages, with differential ABA content, the expression levels of the ABA-related genes PP2CA and ABI1 were significantly upregulated and those of ABA1 and ABA2 were significantly downregulated compared with the WT. AhMYB44-05 showed similar downregulated expression as AhMYB44-16 under drought stress, but its overexpression in Arabidopsis did not significantly affect the drought resistance of transgenic plants. Based on the results, we propose that AhMYB44-11 plays a role as a positive factor in drought tolerance by increasing the transcription abundance of stress-related genes and the accumulation of osmolytes, while AhMYB44-16 negatively regulates drought tolerance through its involvement in ABA-dependent stress response pathways.

Molecular mechanisms of resistance to Myzus persicae conferred by the peach Rm2 gene: A multi-omics view

The transcriptomic and metabolomic responses of peach to Myzus persicae infestation were studied in Rubira, an accession carrying the major resistance gene Rm2 causing antixenosis, and GF305, a susceptible accession. Transcriptome and metabolome showed both a massive reconfiguration in Rubira 48 hours after infestation while GF305 displayed very limited changes. The Rubira immune system was massively stimulated, with simultaneous activation of genes encoding cell surface receptors involved in pattern-triggered immunity and cytoplasmic NLRs (nucleotide-binding domain, leucine-rich repeat containing proteins) involved in effector-triggered immunity. Hypersensitive reaction featured by necrotic lesions surrounding stylet punctures was supported by the induction of cell death stimulating NLRs/helpers couples, as well as the activation of H₂O₂-generating metabolic pathways: photorespiratory glyoxylate synthesis and activation of the futile P5C/proline cycle. The triggering of systemic acquired resistance was suggested by the activation of pipecolate pathway and accumulation of this defense hormone together with salicylate. Important reduction in carbon, nitrogen and sulphur metabolic pools and the repression of many genes related to cell division and growth, consistent with reduced apices elongation, suggested a decline in the nutritional value of apices. Finally, the accumulation of caffeic acid conjugates pointed toward their contribution as deterrent and/or toxic compounds in the mechanisms of resistance.

Promoter cloning of PuLOX2S gene from "Nanguo" pears and screening of transcription factors by Y1H technique

Our previous study on differential proteome and transcriptome of refrigerated "Nanguo" pears found that the PuLOX2S gene was very active in the LOX pathway of aroma synthesis, but the regulation of expression behavior of the gene and how to mediate the aroma synthesis were still unknown. Partial genome sequences of PuLOX2S were cloned, and its promoter was analyzed by Tail-PCR. The PuLOX2S promoter sequences of 610 bp were isolated and identified using Plant CARE, which were composed of cis-acting elements, such as ABRE, AE-box, ARE, CAAT-box, Box 4, TCCC-motif, CAT-box, CGTCA-motif, G-Box, TATA-box, TCA-element, TGA-element, and TGACG-motif. The Y1H technology was used to determine whether proteins interacted with PuLOX2S based on the pGADT7-Chinese white pear cDNA library. The Y1H results were shown that 52 proteins could interact with the PuLOX2S promoter, which was compared with sequences in the GenBank database. The three genes PuERF12, PuMYB44, and PuRF2a were the candidate transcription factors of PuLOX2S and PuCDPK10 played an important role in the gene expression in Nanguo pears. Therefore, the results of this study supply important information for revealing new function of PuLOX2S and the regulation mechanism of expression behavior of the gene. It provides new ideas for the regulation of aroma synthesis in Nanguo pears. PRACTICAL APPLICATIONS: The gene PuLOX2S was very active in the LOX pathway of aroma synthesis, but the regulation of expression behavior of the gene and how to mediate the aroma synthesis were still unknown. We have successfully cloned the partial sequence of the gene and the 610 bp promoter sequence upstream of PuLOX2S and analyzed the structure of cis-acting elements. There are 52 proteins that interact with the PuLOX2S promoter revealed by the Y1H technique. Three transcription factors among the proteins can regulate the level of PuLOX2S expression, which provides new ideas for the regulation of aroma synthesis in "Nanguo" pears. Moreover, the study results could supply scientific information for the quality improvement and genetic modification of Nanguo pears.

Comprehensive analysis of the MYB transcription factor gene family in Morus alba

BACKGROUND

The V-myb myeloblastosis viral oncogene homolog (MYB) family of proteins is large, containing functionally diverse transcription factors. However, MYBs in Morus are still poorly annotated and a comprehensive functional analysis of these transcription factors is lacking.

RESULTS

In the present study, a genome-wide identification of MYBs in Morus alba was performed. In total 166 MaMYBs were identified, including 103 R2R3-MYBs and four 3R-MaMYBs. Comprehensive analyses, including the phylogenetic analysis with putative functional annotation, motif and structure analysis, gene structure organization, promoter analysis, chromosomal localization, and syntenic relationships of R2R3-MaMYBs and 3R-MaMYBs, provided primary characterization for these MaMYBs. R2R3-MaMYBs covered the subgroups reported for R2R3-MYBs in Arabidopsis and Populus, and had two Morus-specific subgroups, indicating the high retention of MYBs in Morus. Motif analysis revealed high conservative residues at the start and end of each helix and residues consisting of the third helix in R2 and R3 repeats. Thirteen intron/exon patterns (a-m) were summarized, and the intron/exon pattern of two introns with phase numbers of 0 and 2 was the prevalent pattern for R2R3-MaMYBs. Various cis-elements in promoter regions were identified, and were mainly related to light response, development, phytohormone response, and abiotic and biotic stress response and secondary metabolite production. Expression patterns of R2R3-MaMYBs in different organs showed that MaMYBs involved in secondary cell wall components and stress responsiveness were preferentially expressed in roots or stems. R2R3-MaMYBs involved in flavonoid biosynthesis and anthocyanin accumulation were identified and characterized based on functional annotation and correlation of their expression levels with anthocyanin contents.

CONCLUSION

Based on a comprehensive analysis, this work provided functional annotation for R2R3-MYBs and an informative reference for further functional dissection of MYBs in Morus.

HbMYB44, a Rubber Tree MYB Transcription Factor With Versatile Functions in Modulating Multiple Phytohormone Signaling and Abiotic Stress Responses

The vital roles of R2R3-MYB transcription factors (TFs) in regulating stress response and phytohormone signaling have been thoroughly studied in numerous plant species, but the functions of these TFs in rubber tree are poorly understood. Rubber tree is the most important source of natural rubber but often suffers from various abiotic and biotic stresses that cause severe yield losses each year. In this study, we reported a novel MYB44 gene in rubber tree (named HbMYB44) and revealed its biological function. HbMYB44 was highly similar to AtMYB44 and clustered into subgroup 22. Transient expression indicated that HbMYB44 is a nuclear localized protein and displays transactivation activity at the C-terminus. HbMYB44 was ubiquitously expressed in rubber tree, and its expression was strongly induced by multiple phytohormones, drought stress, wounding, and H₂O₂ treatments. Furthermore, overexpression of HbMYB44 in Arabidopsis (OE) demonstrated that OE plants significantly enhanced stress tolerance, i.e., salt stress, osmotic stress, and drought stress. Additionally, HbMYB44 promoted recovery from root growth inhibition of OE plants caused by exogenous phytohormones (including abscisic acid, methyl jasmonic acid, gibberellic acid 3, and salicylic acid), but the opposite effect was present in response to ethephon. Interestingly, HbMYB44 increased the expression of its homologous genes and interacting protein-encoding genes in OE plants. Overall, HbMYB44 plays versatile functions in modulating multiple phytohormone signaling pathways and stress tolerance.

Transcriptomic Analysis of Fusarium oxysporum Stress-Induced Pathosystem and Screening of Fom-2 Interaction Factors in Contrasted Melon Plants

Fusarium wilt is one of the most destructive and less controllable diseases in melon, which is usually caused by fusarium oxysporum. In this study, transcriptome sequencing and Yeast Two-Hybrid (Y2H) methods were used for quantification of differentially expressed genes (DEGs) involved in fusarium oxysporum (f. sp. melonis race 1) stress-induced mechanisms in contrasted melon varieties (M4-45 "susceptible" and MR-1 "resistant"). The interaction factors of Fom-2 resistance genes were also explored in response to the plant-pathogen infection mechanism. Transcriptomic analysis exhibited total 1,904 new genes; however, candidate DEGs analysis revealed a total of 144 specific genes (50 upregulated and 94 downregulated) for M4-45 variety and 104 specific genes (71 upregulated and 33 downregulated) for MR-1 variety, respectively. The analysis of Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway depicted some candidate DEGs, including Phenylalanine metabolism, phenylpropane biosynthesis, plants-pathogen interaction, and signal transduction of plant hormones, which were mainly involved in disease resistance metabolic pathways. The weighted gene co-expression network analysis (WGCNA) analysis revealed a strong correlation module and exhibited the disease resistance-related genes encoding course proteins, transcription factors, protein kinase, benzene propane biosynthesis path, plants-pathogen interaction pathway, and glutathione S-transferase. Meanwhile, the resistance-related specific genes expression was relatively abundant in MR-1 compared to the M4-45, and cell wall-associated receptor kinases (MELO3C008452 and MELO3C008453), heat shock protein (Cucumis_melo_newGene_172), defensin-like protein (Cucumis_melo_newGene_5490), and disease resistance response protein (MELO3C016325), activator response protein (MELO3C021623), leucine-rich repeat receptor protein kinase (MELO3C024412), lactyl glutathione ligase (Cucumis_melo_newGene_36), and unknown protein (MELO3C007588) were persisted by exhibiting the upregulated expressions. At the transcription level, the interaction factors between the candidate genes in response to the fusarium oxysporum induced stress, and Y2H screening signified the main contribution of MYB transcription factors (MELO3C009678 and MELO3C014597), BZIP (MELO3C011839 and MELO3C019349), unknown proteins, and key enzymes in the ubiquitination process (4XM334FK014). The candidate genes were further verified in exogenously treated melon plants with f. oxysporum (Fom-2, Race 1), Abscisic acid (ABA), Methyl Jasmonite (MeJA), and Salicylic acid (SA), using the fluorescence quantitative polymerase chain reaction (qRT-PCR) analysis. The overall expression results indicated that the SA signal pathway is involved in effective regulation of the Fom-2 gene activity.

Response of hrpZPsph-transgenic N. benthamiana plants under cadmium stress

The hrpZPsph gene from Pseudomonas syringae pv. phaseolicola, in its secretable form (SP/hrpZPsph), has previously proven capable of conferring resistance against rhizomania disease as well as abiotic stresses in Nicotiana benthamiana plants, while enhancing plant growth. This study aimed at investigating the response of SP/hrpZPsph-expressing plants under cadmium stress. Transgenic N. benthamiana lines, homozygous for the SP/hrpZPsph gene, and wild-type plants were exposed to Cd at different stress levels (0, 50, 100, 150 μΜ CdCl2). Plants' response to stress was assessed at germination and at the whole plant level on the basis of physiological and growth parameters, including seed germination percentage, shoot and root length, total chlorophyll content, fresh and dry root weight, as well as overall symptomatology, and Cd content in leaves and roots. At germination phase, significant differences were noted in germination rates and post-germination growth among stress levels, with Cd effects being in most cases analogous to the level applied but also among plant categories. Although seedling growth was adversely affected in all plant categories, especially at high stress level, lines #6 and #9 showed the lowest decrease in root and shoot length over control. The superiority of these lines was further manifested at the whole plant level by the absence of stress-attributed symptoms and the low or zero reduction in chlorophyll content. Interestingly, a differential tissue-specific Cd accumulation pattern was observed in wt- and hrpZPsph-plants, with the former showing an increased Cd content in leaves and the latter retaining Cd in the roots. These data are discussed in the context of possible mechanisms underlying the hrpZPsph-based Cd stress resistance.

Association Mapping of Seed Quality Traits Under Varying Conditions of Nitrogen Application in Brassica juncea L. Czern & Coss

Indian mustard (Brassica juncea) is a major source of vegetable oil in the Indian subcontinent. The seed cake left after the oil extraction is used as livestock feed. We examined the genetic architecture of oil, protein, and glucosinolates by conducting a genome-wide association study (GWAS), using an association panel comprising 92 diverse genotypes. We conducted trait phenotyping over 2 years at two levels of nitrogen (N) application. Genotyping by sequencing was used to identify 66,835 loci, covering 18 chromosomes. Genetic diversity and phenotypic variations were high for the studied traits. Trait performances were stable when averaged over years and N levels. However, individual performances differed. General and mixed linear models were used to estimate the association between the SNP markers and the seed quality traits. Population structure, principal components (PCs) analysis, and discriminant analysis of principal components (DAPCs) were included as covariates to overcome the bias due to the population stratification. We identified 16, 23, and 27 loci associated with oil, protein, and glucosinolates, respectively. We also established LD patterns and haplotype structures for the candidate genes. The average block sizes were larger on A-genome chromosomes as compared to the B- genome chromosomes. Genetic associations differed over N levels. However, meta-analysis of GWAS datasets not only improved the power to recognize associations but also helped to identify common SNPs for oil and protein contents. Annotation of the genomic region around the identified SNPs led to the prediction of 21 orthologs of the functional candidate genes related to the biosynthesis of oil, protein, and glucosinolates. Notable among these are: LACS5 (A09), FAD6 (B05), ASN1 (A06), GTR2 (A06), CYP81G1 (B06), and MYB44 (B06). The identified loci will be very useful for marker-aided breeding for seed quality modifications in B. juncea.

Dodder-transmitted mobile signals prime host plants for enhanced salt tolerance

The dodders (Cuscuta spp.) are a genus of shoot parasites. In nature, a dodder often simultaneously parasitizes two or more neighboring hosts. Salt stress is a common abiotic stress for plants. It is unclear whether dodder transmits physiologically relevant salt stress-induced systemic signals among its hosts and whether these systemic signals affect the hosts' tolerance to salt stress. Here, we simultaneously parasitized two or more cucumber plants with dodder. We found that salt treatment of one host highly primed the connected host, which showed strong decreases in the extent of leaf withering and cell death in response to subsequent salt stress. Transcriptomic analysis indicated that 24 h after salt treatment of one cucumber, the transcriptome of the other dodder-connected cucumber largely resembled that of the salt-treated one, indicating that inter-plant systemic signals primed these dodder-connected cucumbers at least partly through transcriptomic reconfiguration. Furthermore, salt treatment of one of the cucumbers induced physiological changes, including altered proline contents, stomatal conductance, and photosynthetic rates, in both of the dodder-connected cucumbers. This study reveals a role of dodder in mediating salt-induced inter-plant signaling among dodder-connected hosts and highlights the physiological function of these mobile signals in plant-plant interactions under salt stress.

Candidate genes for grape white rot resistance based on SMRT and Illumina sequencing

BACKGROUND

White rot is one of the most dangerous fungal diseases and can considerably affect grape berry production and quality. However, few studies have focused on this disease, and thus, finding candidate white rot resistance genes is of great importance for breeding resistant grapevine cultivars. Based on field observations and indoor experiments, the cultivars "Victoria" and "Zhuosexiang" showed significant differences in white rot resistance. For understanding the molecular mechanisms behind it, different phenotypes of grapevine leaves were used for RNA sequencing via Illumina and single-molecule real-time (SMRT) sequencing technology.

RESULTS

A transcript library containing 53,906 reads, including known and novel transcripts, was constructed following the full-length transcriptome sequencing of the two grapevine cultivars. Genes involved in salicylic acid (SA) and jasmonic acid (JA) synthesis pathways showed different expression levels. Furthermore, four key transcription factors (TFs), NPR1, TGA4, Pti6, and MYC2, all involved in the SA and JA signal pathways were identified, and the expression profile revealed the different regulation of the pathogenesis related protein1 (PR1) resistance gene, as mediated by the four TFs.

CONCLUSIONS

Full-length transcript sequencing can substantially improve the accuracy and integrity of gene prediction and gene function research in grapevine. Our results contribute to identify candidate resistance genes and improve our understanding of the genes and regulatory mechanisms involved in grapevine resistance to white rot.

Overexpression of CmMYB15 provides chrysanthemum resistance to aphids by regulating the biosynthesis of lignin

MYB transcription factors are widely involved in the development of and physiological processes in plants. Here, we isolated the chrysanthemum R2R3-MYB family transcription factor CmMYB15, a homologous gene of AtMYB15. It was demonstrated that CmMYB15 expression was induced by aphids and that CmMYB15 could bind to AC elements, which usually exist in the promoter of lignin biosynthesis genes. Overexpression of CmMYB15 in chrysanthemum enhanced the resistance of aphids. Additionally, the content of lignin and the expression of several lignin biosynthesis genes increased. In summary, the results indicate that CmMYB15 regulates lignin biosynthesis genes that enhance the resistance of chrysanthemum to aphids.

AtMYB44 interacts with TOPLESS-RELATED corepressors to suppress protein phosphatase 2C gene transcription

AtMYB44 has been described in diverse hormonal signaling processes including abscisic acid (ABA)-mediated tolerance to abiotic stress; however, its function as a transcription factor is controversial. AtMYB44 contains the amino acid sequence LSLSL, a putative ETHYLENE-RESPONSIVE ELEMENT BINDING FACTOR-ASSOCIATED AMPHIPHILIC REPRESSION (EAR) motif. In yeast two-hybrid assay, physical interaction between AtMYB44 and a TOPLESS-RELATED (TPR) corepressor was observed, but abolished by mutation of the EAR motif. We performed bimolecular fluorescence complementation assay to confirm their interaction in planta. Chromatin immunoprecipitation assay revealed binding of AtMYB44 to the promoter regions of clade A protein phosphatase 2C (PP2C) genes (e.g., ABI1, ABI2, and HAI1), implying putative targets. Levels of histone H3 acetylation around the promoter regions were markedly lower in AtMYB44-overexpressing (35S:AtMYB44) plants than in wild-type plants. These results suggest that AtMYB44 forms a complex with TPR corepressors and recruits histone deacetylase(s) to suppress PP2C gene transcription in a signal-independent manner.

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.

Overexpression of SSBXoc, a Single-Stranded DNA-Binding Protein From Xanthomonas oryzae pv. oryzicola, Enhances Plant Growth and Disease and Salt Stress Tolerance in Transgenic Nicotiana benthamiana

We previously reported that SSBXoc, a highly conserved single-stranded DNA-binding protein from Xanthomonas spp., was secreted through the type III secretion system (T3SS) and functioned as a harpin-like protein to elicit the hypersensitive response (HR) in the non-host plant, tobacco. In this study, we cloned SsbXoc gene from X. oryzae pv. oryzicola (Xoc), the causal agent of bacterial leaf streak in rice, and transferred it into Nicotiana benthamiana via Agrobacterium-mediated transformation. The expression of SsbXoc in transgenic N. benthamiana enhanced growth of both seedling and adult plants. When inoculated with the harpin Hpa1 or the pathogen Pseudomonas syringae pv. tomato DC3000 (Pst DC3000), the accumulation of reactive oxygen species (ROS) was increased more in SsbXoc transgenic lines than that in wild-type (WT) plants. The expression of pathogenesis-related protein genes (PR1a and SGT1), HR marker genes (HIN1 and HSR203J) and the mitogen-activated protein kinase pathway gene, MPK3, was significantly higher in transgenic lines than in WT after inoculation with Pst DC3000. In addition, SsbXoc transgenic lines showed the enhanced resistance to the pathogenic bacteria P. s. tabaci and the improved tolerance to salt stress, accompanied by the elevated transcription levels of the defense- and stress-related genes. Taken together, these results indicate that overexpression of the SsbXoc gene in N. benthamiana significantly enhanced plant growth and increased tolerance to disease and salt stress via modulating the expression of the related genes, thus providing an alternative approach for development of plants with improved tolerance against biotic and abiotic stresses.

Arabidopsis Transcription Factor MYB102 Increases Plant Susceptibility to Aphids by Substantial Activation of Ethylene Biosynthesis

Induction of ethylene biosynthesis by aphids increases the susceptibility of several plant species to aphids. Recent studies have indicated that some MYB transcription factors regulate the phloem-based defense against aphid infestation by modulating ethylene (ET) signaling. Arabidopsis MYB102 has previously been shown to be induced by wound signaling and regulate defense response against chewing insects. However, it remains unclear whether ArabidopsisMYB102 takes part in the defense response of plants to aphids. Here, we investigated the function of MYB102 in the response of Arabidopsis to aphid infestation. ArabidopsisMYB102 was primarily expressed in vascular tissues, and its transcription was remarkably induced by green peach aphids (GPA; Myzus persicae). The results of RNA-Sequencing revealed that overexpression of MYB102 in Arabidopsis promoted ET biosynthesis by upregulation of some 1-aminocyclopropane-1-carboxylate synthase (ACS) genes, which are rate-limiting enzymes of the ET-synthetic pathway. Enhanced ET levels led to reduced Arabidopsis resistance to GPA. Furthermore, dominant suppression of MYB102 inhibited aphid-induced increase of ET levels in Arabidopsis. In agreement with a negative regulatory role for ET in aphid defense responses, the MYB102-overexpressing lines were more susceptible to GPA than wild-type (WT) plants. Overexpression of MYB102 in Arabidopsis obviously repressed aphid-induced callose deposition. Conversely, overexpression of MYB102 failed to increase aphid susceptibility in both the ET-insensitive mutants and plants treated with inhibitors of ET signaling pathways, demonstrating that the ET was critical for promoting aphid performance conferred by overexpression of MYB102. Collectively, our findings indicate that the Arabidopsis MYB102 increases host susceptibility to GPA through the ET-dependent signaling pathways.

Three MYB genes co-regulate the phloem-based defence against English grain aphid in wheat

Plant phloem-based defence (PBD) against phloem-feeding insects is characteristic of the sieve occlusion by phloem lectins and β-1,3-glucan callose, both of which are produced under regulation by ethylene and MYB transcription factors. Wheat PBD requires β-1,3-glucan synthase-like proteins GSL2, GSL10, and GSL12, and may also require insect-resistant mannose-binding lectins Hfr-1 and Wci-1, which can accumulate in the phloem upon aphid feeding. This study elucidates whether any of the 73 MYB genes identified previously in the common wheat Triticum aestivum genome plays a role in wheat PBD activation with regard to the GSLs and lectins. Wheat MYB genes TaMYB19, TaMYB29, and TaMYB44 are highly activated in response to infestation of English grain aphid, and their silencing facilitates aphid feeding on wheat phloem and represses wheat PBD responses. Repressed PBD is shown to decrease aphid-induced callose deposition in wheat leaf epidermis and decrease aphid-induced expression of genes GSL2, GSL10, GSL12, Hfr-1, and Wci-1 in wheat leaf tissues. Based on single gene silencing effects, TaMYB19, TaMYB29, and TaMYB44 contribute 55-82% of PBD responses. However, the contributions of TaMYB genes to PBD are eliminated by ethylene signalling inhibitors, while simultaneous silencing of the three TaMYB genes cancels the tested PBD responses. Therefore, TaMYB19, TaMYB29, and TaMYB44 are co-regulators of wheat PBD and execute this function through crosstalk with the ethylene signalling pathway.

CmMYB19 Over-Expression Improves Aphid Tolerance in Chrysanthemum by Promoting Lignin Synthesis

The gene encoding the MYB (v-myb avian myeloblastosis vira l oncogene homolog) transcription factor CmMYB19 was isolated from chrysanthemum. It encodes a 200 amino acid protein and belongs to the R2R3-MYB subfamily. CmMYB19 was not transcriptionally activated in yeast, while a transient expression experiment conducted in onion epidermal cells suggested that the CmMYB19 product localized to the nucleus. CmMYB19 transcription was induced by aphid (Macrosiphoniella sanborni) infestation, and the abundance of transcript was higher in the leaf and stem than in the root. The over-expression of CmMYB19 restricted the multiplication of the aphids. A comparison of transcript abundance of the major genes involved in lignin synthesis showed that CmPAL1 (phenylalanine ammonia lyase 1), CmC4H (cinnamate4 hydroxylase), Cm4CL1 (4-hydroxy cinnamoyl CoA ligase 1), CmHCT (hydroxycinnamoyl CoA-shikimate/quinate hydroxycinnamoyl transferase), CmC3H1 (coumarate3 hydroxylase1), CmCCoAOMT1 (caffeoyl CoA O-methyltransferase 1) and CmCCR1 (cinnamyl CoA reductase1) were all upregulated, in agreement with an increase in lignin content in CmMYB19 over-expressing plants. Collectively, the over-expression of CmMYB19 restricted the multiplication of the aphids on the host, mediated by an enhanced accumulation of lignin.

AtMYB44 Positively Regulates the Enhanced Elongation of Primary Roots Induced by N-3-Oxo-Hexanoyl-Homoserine Lactone in Arabidopsis thaliana

N-acyl-homoserine lactones (AHL) are the quorum-sensing (QS) signal molecules used by many gram-negative bacteria to coordinate their collective behavior in a population. Recent evidence demonstrates their roles in plant root growth and defense responses. AtMYB44 is a multifaceted transcriptional factor that functions in many physiological processes in plants but whether AtMYB44 modulates the plant response to AHL with aspects of primary root elongation remains unknown. Here, we show that the expression of AtMYB44 was upregulated upon treatment with N-3-oxo-hexanoyl-homoserine lactone (3OC6-HSL). The stimulatory effect of 3OC6-HSL on primary root elongation was abolished in the AtMYB44 functional-deficiency mutant atmby44. In contrast, an enhanced promoting-impact of 3OC6-HSL on primary root growth was observed in AtMYB44-overexpressing plant MYB44OTA. Cellular analysis indicated that the prolonged primary root elicited by 3OC6-HSL is the consequence of increased cell division in the meristem zone and enhanced cell elongation in the elongation zone, and AtMYB44 may act as a positive regulator in this process. Furthermore, we demonstrated that AtMYB44 might participate in the 3OC6-HSL-mediated primary root growth via regulating the expression of cytokinin- and auxin-related genes. The data establish a genetic connection between the regulatory role of AtMYB44 in phytohormones-related gene expression and plant response to the bacterial QS signal.

Transcriptome Analysis of Ramie (Boehmeria nivea L. Gaud.) in Response to Ramie Moth (Cocytodes coerulea Guenée) Infestation

The ramie moth Cocytodes coerulea Guenée (RM) is an economically important pest that seriously impairs the yield of ramie, an important natural fiber crop. The molecular mechanisms that underlie the ramie-pest interactions are unclear up to date. Therefore, a transcriptome profiling analysis would aid in understanding the ramie defense mechanisms against RM. In this study, we first constructed two cDNA libraries derived from RM-challenged (CH) and unchallenged (CK) ramie leaves. The subsequent sequencing of the CH and CK libraries yielded 40.2 and 62.8 million reads, respectively. Furthermore, de novo assembling of these reads generated 26,759 and 29,988 unigenes, respectively. An integrated assembly of data from these two libraries resulted in 46,533 unigenes, with an average length of 845 bp per unigene. Among these genes, 24,327 (52.28%) were functionally annotated by predicted protein function. A comparative analysis of the CK and CH transcriptome profiles revealed 1,980 differentially expressed genes (DEGs), of which 750 were upregulated and 1,230 were downregulated. A quantitative real-time PCR (qRT-PCR) analysis of 13 random selected genes confirmed the gene expression patterns that were determined by Illumina sequencing. Among the DEGs, the expression patterns of transcription factors, protease inhibitors, and antioxidant enzymes were studied. Overall, these results provide useful insights into the defense mechanism of ramie against RM.

Plant MYB Transcription Factors: Their Role in Drought Response Mechanisms

Water scarcity is one of the major causes of poor plant performance and limited crop yields worldwide and it is the single most common cause of severe food shortage in developing countries. Several molecular networks involved in stress perception, signal transduction and stress responses in plants have been elucidated so far. Transcription factors are major players in water stress signaling. In recent years, different MYB transcription factors, mainly in Arabidopsis thaliana (L.) Heynh. but also in some crops, have been characterized for their involvement in drought response. For some of them there is evidence supporting a specific role in response to water stress, such as the regulation of stomatal movement, the control of suberin and cuticular waxes synthesis and the regulation of flower development. Moreover, some of these genes have also been characterized for their involvement in other abiotic or biotic stresses, an important feature considering that in nature, plants are often simultaneously subjected to multiple rather than single environmental perturbations. This review summarizes recent studies highlighting the role of the MYB family of transcription factors in the adaptive responses to drought stress. The practical application value of MYBs in crop improvement, such as stress tolerance engineering, is also discussed.

Recessive mutation identifies auxin-repressed protein ARP1, which regulates growth and disease resistance in tobacco

To study the molecular mechanism that underpins crosstalk between plant growth and disease resistance, we performed a mutant screening on tobacco and created a recessive mutation that caused the phenotype of growth enhancement and resistance impairment (geri1). In the geri1 mutant, growth enhancement accompanies promoted expression of growth-promoting genes, whereas repressed expression of defense response genes is consistent with impaired resistance to diseases caused by viral, bacterial, and oomycete pathogens. The geri1 allele identifies a single genetic locus hypothetically containing the tagged GERI1 gene. The isolated GERI1 gene was predicted to encode auxin-repressed protein ARP1, which was determined to be 13.5 kDa in size. The ARP1/GERI1 gene was further characterized as a repressor of plant growth and an activator of disease resistance based on genetic complementation, gene silencing, and overexpression analyses. ARP1/GERI1 resembles pathogen-associated molecular patterns and is required for them to repress plant growth and activate plant immunity responses. ARP1/GERI1 represses growth by inhibiting the expression of AUXIN RESPONSE FACTOR gene ARF8, and ARP1/GERI1 recruits the NPR1 gene, which is essential for the salicylic-acid-mediated defense, to coregulate disease resistance. In conclusion, ARP1/GERI1 is an integral regulator for crosstalk between growth and disease resistance in the plant.

Transgenic expression of a functional fragment of harpin protein Hpa1 in wheat induces the phloem-based defence against English grain aphid

The harpin protein Hpa1 has multiple beneficial effects in plants, promoting plant growth and development, increasing crop yield, and inducing resistance to pathogens and insect pests. For these effects, the 10-40 residue fragment (Hpa1₁₀₋₄₂) isolated from the Hpa1 sequence is 1.3- to 7.5-fold more effective than the full-length protein. Here it is reported that the expression of Hpa1₁₀₋₄₂ under the direction of an insect-induced promoter induces the phloem-based defence to English grain aphid, a dominant species of wheat aphids. The expression of Hpa1₁₀₋₄₂ was found to compromise the colonization preference of aphids on the plant and further inhibit aphid reproduction in leaf colonies. In Hpa1₁₀₋₄₂-expressing wheat lines, moreover, aphid feeding from the phloem was repressed in correlation with the phloem-based defence. This defensive mechanism was shown as enhanced expression of wheat genes encoding phloem lectin proteins (PP2-A1 and PP2-A2) and β-1,3-glucan synthase-like enzymes (GSL2, GSL10, and GSL12). Both PP2-A and β-1,3-glucan formed high molecular mass polymers to block phloem sieve plate pores and therefore impede aphid feeding from the phloem. However, the phloem-based defence was impaired by treating plants with ethylene signalling inhibitors, suggesting the requirement for the ethylene signalling pathway. In addition, if Hpa1₁₀₋₄₂-expressing plants were subjected to attack by a small number of aphids, they newly acquired agriculturally beneficial characters, such as enhanced vegetative growth and increased tiller numbers and grain output values. These results suggest that the defensive and developmental roles of Hpa1₁₀₋₄₂ can be integrated into the germplasm of this agriculturally significant crop.

Plant growth enhancement and associated physiological responses are coregulated by ethylene and gibberellin in response to harpin protein Hpa1

The harpin protein Hpa1 produced by the bacterial blight pathogen of rice induces several growth-promoting responses in plants, activating the ethylene signaling pathway, increasing photosynthesis rates and EXPANSIN (EXP) gene expression levels, and thereby enhancing the vegetative growth. This study was attempted to analyze any mechanistic connections among the above and the role of gibberellin in these responses. Hpa1-induced growth enhancement was evaluated in Arabidopsis, tomato, and rice. And growth-promoting responses were determined mainly as an increase of chlorophyll a/b ratio, which indicates a potential elevation of photosynthesis rates, and enhancements of photosynthesis and EXP expression in the three plant species. In Arabidopsis, Hpa1-induced growth-promoting responses were partially compromised by a defect in ethylene perception or gibberellin biosynthesis. In tomato and rice, compromises of Hpa1-induced growth-promoting responses were caused by a pharmacological treatment with an ethylene perception inhibitor or a gibberellin biosynthesis inhibitor. In the three plant species, moreover, Hpa1-induced growth-promoting responses were significantly impaired, but not totally eliminated, by abolishing ethylene perception or gibberellin synthesis. However, simultaneous nullifications in both ethylene perception and gibberellin biosynthesis almost canceled the full effects of Hpa1 on plant growth, photosynthesis, and EXP2 expression. Theses results suggest that ethylene and gibberellin coregulate Hpa1-induced plant growth enhancement and associated physiological and molecular responses.