Comparative transcriptome analysis uncovers regulatory roles of long non-coding RNAs involved in resistance to powdery mildew in melon.

BACKGROUND: Long non-coding RNAs (lncRNAs) are a class of non-coding RNAs with more than 200 nucleotides in length, which play vital roles in a wide range of biological processes. Powdery mildew disease (PM) has become a major threat to the production of melon. To investigate the potential roles of lncRNAs in resisting to PM in melon, it is necessary to identify lncRNAs and uncover their molecular functions. In this study, we compared the lncRNAs between a resistant and a susceptible melon in response to PM infection. RESULTS: It is reported that 11,612 lncRNAs were discovered, which were distributed across all 12 melon chromosomes, and > 85% were from intergenic regions. The melon lncRNAs have shorter transcript lengths and fewer exon numbers than protein-coding genes. In addition, a total of 407 and 611 lncRNAs were found to be differentially expressed after PM infection in PM-susceptible and PM-resistant melons, respectively. Furthermore, 1232 putative targets of differently expressed lncRNAs (DELs) were discovered and gene ontology enrichment (GO) analysis showed that these target genes were mainly enriched in stress-related terms. Consequently, co-expression patterns between LNC_018800 and CmWRKY21, LNC_018062 and MELO3C015771 (glutathione reductase coding gene), LNC_014937 and CmMLO5 were confirmed by qRT-PCR. Moreover, we also identified 24 lncRNAs that act as microRNA (miRNA) precursors, 43 lncRNAs as potential targets of 22 miRNA families and 13 lncRNAs as endogenous target mimics (eTMs) for 11 miRNAs. CONCLUSION: This study shows the first characterization of lncRNAs involved in PM resistance in melon and provides a starting point for further investigation into the functions and regulatory mechanisms of lncRNAs in the resistance to PM.

Identification and characterization of melon circular RNAs involved in powdery mildew responses through comparative transcriptome analysis.

Circular RNAs (circRNAs) are a class of newly discovered non-coding RNAs that are typically derived from a genome's exonic, intronic, and intergenic regions. Recent studies of circRNAs in animals and plants have shown that circRNAs are vital in response to various abiotic and biotic stresses. Powdery mildew disease (PM) is a serious fungal disease threatening the melon industry. We performed whole transcriptome sequencing using the leaves of a PM-resistant (M1) and a PM-susceptible (B29) melon to identify circRNAs and determine their molecular functions. A total of 303 circRNAs were identified and >50% circRNAs were derived from exonic regions. Expression levels were significantly altered in 17 and 23 circRNAs after PM infections in B29 and M1, respectively. Melon circRNAs may participate in the response to biotic stimuli, oxidation reduction, metabolic processes, and the regulation of gene expression based on the functional annotation of circRNA parental genes. Furthermore, 27 circRNAs were predicted to be potential targets or 'sponges' for 18 microRNAs (miRNAs). Our results are the first to identify and characterize circRNA functions in melon and may contribute to a better understanding of the role and regulatory mechanisms of circRNAs in resisting PM.

Genome-wide characterization, evolutionary analysis of WRKY genes in Cucurbitaceae species and assessment of its roles in resisting to powdery mildew disease.

The WRKY proteins constitute a large family of transcription factors that have been known to play a wide range of regulatory roles in multiple biological processes. Over the past few years, many reports have focused on analysis of evolution and biological function of WRKY genes at the whole genome level in different plant species. However, little information is known about WRKY genes in melon (Cucumis melo L.). In the present study, a total of 56 putative WRKY genes were identified in melon, which were randomly distributed on their respective chromosomes. A multiple sequence alignment and phylogenetic analysis using melon, cucumber and watermelon predicted WRKY domains indicated that melon WRKY proteins could be classified into three main groups (I-III). Our analysis indicated that no recent duplication events of WRKY genes were detected in melon, and strong purifying selection was observed among the 85 orthologous pairs of Cucurbitaceae species. Expression profiles of CmWRKY derived from RNA-seq data and quantitative RT-PCR (qRT-PCR) analyses showed distinct expression patterns in various tissues, and the expression of 16 CmWRKY were altered following powdery mildew infection in melon. Besides, we also found that a total of 24 WRKY genes were co-expressed with 11 VQ family genes in melon. Our comparative genomic analysis provides a foundation for future functional dissection and understanding the evolution of WRKY genes in cucurbitaceae species, and will promote powdery mildew resistance study in melon.

Genome-wide analysis of basic/helix-loop-helix gene family in peanut and assessment of its roles in pod development.

The basic/helix-loop-helix (bHLH) proteins constitute a superfamily of transcription factors that are known to play a range of regulatory roles in eukaryotes. Over the past few decades, many bHLH family genes have been well-characterized in model plants, such as Arabidopsis, rice and tomato. However, the bHLH protein family in peanuts has not yet been systematically identified and characterized. Here, 132 and 129 bHLH proteins were identified from two wild ancestral diploid subgenomes of cultivated tetraploid peanuts, Arachis duranensis (AA) and Arachis ipaensis (BB), respectively. Phylogenetic analysis indicated that these bHLHs could be classified into 19 subfamilies. Distribution mapping results showed that peanut bHLH genes were randomly and unevenly distributed within the 10 AA chromosomes and 10 BB chromosomes. In addition, 120 bHLH gene pairs between the AA-subgenome and BB-subgenome were found to be orthologous and 101 of these pairs were highly syntenic in AA and BB chromosomes. Furthermore, we confirmed that 184 bHLH genes expressed in different tissues, 22 of which exhibited tissue-specific expression. Meanwhile, we identified 61 bHLH genes that may be potentially involved in peanut-specific subterranean. Our comprehensive genomic analysis provides a foundation for future functional dissection and understanding of the regulatory mechanisms of bHLH transcription factors in peanuts.