Promoter variations of ClERF1 gene determines flesh firmness in watermelon.

BACKGROUND: Flesh firmness is a critical factor that influences fruit storability, shelf-life and consumer's preference as well. However, less is known about the key genetic factors that are associated with flesh firmness in fresh fruits like watermelon. RESULTS: In this study, through bulk segregant analysis (BSA-seq), we identified a quantitative trait locus (QTL) that influenced variations in flesh firmness among recombinant inbred lines (RIL) developed from cross between the Citrullus mucosospermus accession ZJU152 with hard-flesh and Citrullus lanatus accession ZJU163 with soft-flesh. Fine mapping and sequence variations analyses revealed that ethylene-responsive factor 1 (ClERF1) was the most likely candidate gene for watermelon flesh firmness. Furthermore, several variations existed in the promoter region between ClERF1 of two parents, and significantly higher expressions of ClERF1 were found in hard-flesh ZJU152 compared with soft-flesh ZJU163 at key developmental stages. DUAL-LUC and GUS assays suggested much stronger promoter activity in ZJU152 over ZJU163. In addition, the kompetitive allele-specific PCR (KASP) genotyping datasets of RIL populations and germplasm accessions further supported ClERF1 as a possible candidate gene for fruit flesh firmness variability and the hard-flesh genotype might only exist in wild species C. mucosospermus. Through yeast one-hybrid (Y1H) and dual luciferase assay, we found that ClERF1 could directly bind to the promoters of auxin-responsive protein (ClAux/IAA) and exostosin family protein (ClEXT) and positively regulated their expressions influencing fruit ripening and cell wall biosynthesis. CONCLUSIONS: Our results indicate that ClERF1 encoding an ethylene-responsive factor 1 is associated with flesh firmness in watermelon and provide mechanistic insight into the regulation of flesh firmness, and the ClERF1 gene is potentially applicable to the molecular improvement of fruit-flesh firmness by design breeding.

The coiled-coil protein gene WPRb confers recessive resistance to Cucumber green mottle mosaic virus.

Cucumber green mottle mosaic virus (CGMMV) is one of the major global quarantine viruses and causes severe symptoms in Cucurbit crops, particularly with regard to fruit decay. However, the genetic mechanisms that control plant resistance to CGMMV have yet to be elucidated. Here, we found that WPRb, a weak chloroplast movement under blue light 1 and plastid movement impaired 2-related protein family gene, is recessively associated with CGMMV resistance in watermelon (Citrullus lanatus). We developed a reproducible marker based on a single non-synonymous substitution (G1282A) in WPRb, which can be used for marker-assisted selection for CGMMV resistance in watermelon. Editing of WPRb conferred greater tolerance to CGMMV. We found WPRb targets to the plasmodesmata (PD) and biochemically interacts with the CGMMV movement protein, facilitating viral intercellular movement by affecting the permeability of PD. Our findings enable us to genetically control CGMMV resistance in planta by using precise genome editing techniques targeted to WPRb.

Molecular characterization and pathogenicity of an infectious clone of tomato leaf curl New Delhi virus isolate infecting Cucumis melo.

Tomato leaf curl New Delhi virus (ToLCNDV) is a member of the genus Begomovirus, and causes devastating disease in the world. In recent years, ToLCNDV was rapidly spreading in China and induces severe economic losses in agriculture. In this study, we sequenced and characterized the complete genome of ToLCNDV isolates from melon plants showing leaf curling and stunting symptoms in Jiangsu Province of China. We constructed a full-length infectious cDNA clone of ToLCNDV, which could induce systemic infection with typical symptoms in Nicotiana benthamiana, Citrullus melo, and Citrullus lanatus plants through agrobacterium-mediated inoculation. Further experimental evidence demonstrated that the virions produced in plants infected with the infectious clone of ToLCNDV are biologically active and sap-transmissible. We also evaluated the resistance of commercial melon cultivars to ToLCNDV and found all testing melon cultivars were susceptible to ToLCNDV. Collectively, the reverse genetic system developed herein will facilitate further research on biological functions of proteins encoded by ToLCNDV and plant-ToLCNDV interactions, which might provide new insights into breeding resistance germplasm in crops.

Tomato leaf curl New Delhi virus: an emerging plant begomovirus threatening cucurbit production.

Tomato leaf curl New Delhi virus (ToLCNDV), a bipartite begomovirus, was first reported to infect tomato and has recently spread rapidly as an emerging disease to Cucurbitaceae crops. To date, the virus has been reported to infect more than 11 cucurbit crops, in 16 countries and regions, causing severe yield losses. In autumn 2022, ToLCNDV was first isolated from cucurbit plants in Southeastern coastal areas of China. Phylogenetic analysis established that these isolates belong to the Asian ToLCNDV clade, and shared high nucleotide identity and closest genetic relationship with the DNA-A sequence from the Chinese tomato-infecting ToLCNDV isolate (Accession no. OP356207) and the tomato New Delhi ToLCNDV-Severe isolate (Accession no. HM159454). In this review, we summarize the occurrence and distribution, host range, detection and diagnosis, control strategies, and genetic resistance of ToLCNDV in the Cucurbitaceae. We then summarize pathways that could be undertaken to improve our understanding of this emerging disease, with the objective to develop ToLCNDV-resistant cucurbit cultivars. Supplementary Information: The online version contains supplementary material available at 10.1007/s42994-023-00118-4.

General regulatory factor 3 regulates the expression of alternative oxidase 1a and the biosynthesis of glucosinolates in cytoplasmic male sterile Brassica juncea.

Mitochondrial retrograde signaling (MRS) plays an essential role in sensing and responding to internal and external stimuli to optimize growth to adapt to the prevailing environmental conditions. Previously studies showed alterations on MRS in cytoplasmic male sterile (CMS) plant. However, the regulators involved in MRS in CMS plants remain largely unknown. In this study, we used alternative oxidase 1a (AOX1a) as an indicator of MRS and found that the expression of AOX1a was significantly downregulated in a CMS line comparing to its revertant line, thus indicating an alteration in MRS in the CMS line. By performing a BLAST search of known regulatory components involved in MRS in yeast, we identified general regulatory factor 3 (GRF3), an orthologue of Bmh1/2 in yeast, and demonstrated an association between this gene and MRS in plants, as evidenced by change in AOX1a expression. GRF3 protein was found to be located in the nucleus and the plasma membrane. Further studies showed that GRF3 interacted with MYB29, and regulated the biosynthesis of glucosinolates in Brassica juncea. These findings revealed that GRF3, a negative regulator of AOX1a, is involved in MRS, and also plays a vital role in the accumulation of glucosinolates in CMS crops.