Yoon Jeong Jang

Several Neopestalotiopsis spp. have been reported to affect strawberry worldwide. Here, we sequenced two isolates of Neopestalotiopsis 19-02 (highly virulent) and 13-481 (moderately virulent) recovered from commercial strawberry fields in Florida and generated chromosome-scale assemblies using the Oxford Nanopore Technologies and Illumina platforms. Each genome assembly for 19-02 and 13-481 contained putative telomere sequences at the 5′ and 3′ ends. By analyzing the collinearity of the two newly assembled genomes and verifying the conserved telomere sequence at the end of each chromosome, we confirmed that the genome of Neopestalotiopsis spp. consists of seven basic chromosomes. Benchmarking Universal Single-Copy Orthologs (BUSCO) analysis showed 98.5% of conserved core genes for both genome assemblies, 19-02 and 13-481. Phylogenetic analysis with internal transcribed spacer, beta-tubulin, and translation elongation factor regions obtained from the assemblies 19-02 and 13-481 demonstrated that the highly virulent isolate 19-02 is phylogenetically distinct from moderate virulent N. rosae 13-481. Comparative genome analysis of the high-quality reference genome assemblies provided in this study will facilitate the identification of genomic regions responsible for the different virulence of the Neopestalotiopsis pathogen to strawberry. [Formula: see text] The author(s) have dedicated the work to the public domain under the Creative Commons CC0 “No Rights Reserved” license by waiving all of his or her rights to the work worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law, 2024.

Sugars are the main drivers of strawberry sweetness, and understanding their genetic control is of critical importance for breeding. Large-scale genome-wide association studies were performed in two populations totaling 3399 individuals evaluated for soluble solids content (SSC) and fruit yield. Two stable quantitative trait loci (QTL) on chromosome 3B and 6A for SSC were identified. Favorable haplotypes at both QTL for SSC decreased yield, though optimal allelic combinations were identified with reduced impacts on yield. Metabolites in the starch and sucrose metabolism pathway were characterized and quantified for 23 contrasting genotypes in leaves, white fruit, and red fruit. Variations in sucrose concentrations/efflux indicated genetic variation underlying sucrose accumulation and transportation during fruit ripening. Integration of genome-wide association studies and expression quantitative locus mapping identified starch synthase 4 (FxaC_10g00830) and sugar transporter 2-like candidate genes (FxaC_21g51570) within the respective QTL intervals. These results will enable immediate applications in genomics-assisted breeding for flavor and further study of candidate genes underlying genetic variation of sugar accumulation in strawberry fruit.

Virus-induced gene silencing (VIGS) is a powerful tool for high-throughput analysis of gene function. Here, we developed the VIGS vector pCF93, from which expression of the cucumber fruit mottle mosaic virus genome is driven by the cauliflower mosaic virus 35S promoter to produce viral transcripts in inoculated plants. To test the utility of the pCF93 vector, we identified candidate genes related to male sterility (MS) in watermelon (Citrullus lanatus), which is recalcitrant to genetic transformation. Specifically, we exploited previously reported reference-based and de novo transcriptome data to define 38 differentially expressed genes between a male-sterile line and its fertile near-isogenic line in the watermelon cultivar DAH. We amplified 200- to 300-bp fragments of these genes, cloned them into pCF93, and inoculated DAH with the resulting VIGS clones. The small watermelon cultivar DAH enabled high-throughput screening using a small cultivation area. We simultaneously characterized the phenotypes associated with each of the 38 candidate genes in plants grown in a greenhouse. Silencing of 8 of the 38 candidate genes produced male-sterile flowers with abnormal stamens and no pollen. We confirmed the extent of gene silencing in inoculated flowers using reverse transcription–qPCR. Histological analysis of stamens from male-fertile and male-sterile floral buds and mature flowers revealed developmental defects and shrunken pollen sacs. Based on these findings, we propose that the pCF93 vector and our VIGS system will facilitate high-throughput analysis for the study of gene function in watermelons.