Candidate Susceptibility Genes for Powdery and Downy Mildew in Watermelon and Squash

Abstract

Powdery mildew (PM) caused by Podosphaera xanthii and downy mildew (DM) caused by Pseudoperonospora cubensis are two of the most economically important diseases for watermelon (Citrullus lanatus) and squash (Cucurbita pepo, C. maxima and C. moschata). Traditional breeding for resistance to PM and DM is resource intensive, often requiring decades' long phenotyping and selection processes. As an alternative, durable and broadspectrum resistance to PM and DM can be obtained through loss-of-function of susceptibility genes in elite breeding material. Susceptibility genes for PM [Mildew-Locus-O (MLO) and Powdery Mildew Resistance (PMR)] and DM [Downy Mildew Resistance (DMR)] have been functionally proven in model plant species. Previous studies have reported candidate MLO genes for C. lanatus and C. pepo, but none for C. maxima and C. moschata. On the contrary, no PMR or DMR candidate genes have been identified for C. lanatus or any of the Cucurbita species. The current study used bioinformatics approaches based on sequence similarity, phylogenetic relationships and presence of conserved domains to predict candidate MLO genes in C. maxima and C. moschata and PMR and DMR genes in C. lanatus, C. pepo, C. maxima and C. moschata. Four MLO homologs in C. maxima and five in C. moschata clustered within Clade V, a clade containing all MLO susceptibility genes in dicots, and had highly conserved transmembrane domains and C-terminal PM interaction motif. Sixty-three candidate PMR genes were identified among the four species, 16 of which had close similarity to functionally proven PMR homologs in model species. Similarly, 37 candidate DMR genes were identified 12 among which clustered with functionally proven DMR homologs in model species. Functional analysis of the genes identified in the current study will reveal their role in pathogenesis and assess their potential for manipulation through gene editing methods to generate novel resistant plant genotypes.

A review on the genetic resources, domestication and breeding history of spinach (Spinacia oleracea L.)

“…These genes probably have a conserved function across plant species. Schouten et al (2014) and Porterfield and Meru (2017) used DMR1 and DMR6 to search for novel DMR candidate genes in the Cucurbitaceae family. Huibers et al (2013) studied the DMR1 orthologue in S. lycopersicum (SIDMR1) and found that gene silencing was associated with resistance against late blight caused by the oomycete Phytophthora infestans, although it also caused detrimental effects on plant growth.…”

Whole genome resequencing of four Italian sweet pepper landraces provides insights on sequence variation in genes of agronomic value

“…Then, a second series of k-mers (e.g. : narrow range, [53][54][55][56][57][58][59][60][61][62][63][64][65][66][67][68][69], which revealed the best assembly performances, was scanned. Metrics for assessing the quality of a genome assembly (e.g.…”

“…DMR1 58 . PMR genes are involved in cell wall biology where they mediate structure formation and pectin accumulation 59 . Among them, the PMR5 family was the most represented, totalling from 67 to 69 gene members in the four inbred lines and 72 in CM334' , which were scattered along the genome.…”

“…The less represented S-genes were DMR6, which has been used to trigger broad-spectrum resistance against multiple pathogens and was present in two copies in all the genomes, and the DMR1 and CPR5 genes. The formers have been described to confer resistance to downy mildew in Arabidopsis and tomato by accumulating elevated levels of homoserine 59 , while the latter to be involved in cell proliferation and cell death control 62 . www.nature.com/scientificreports www.nature.com/scientificreports/ S-genes were analyzed for the presence of functional SNPs (Fig.…”