Molecular Pathogens 2024, Vol.15, No.3, 155-169 http://microbescipublisher.com/index.php/mp 162 Figure 4 Genomic regions associated with the resistance to PM (P. xanthii) derived from different sources (Adopted from López-Martín et al., 2022) Image caption: This figure highlights the genomic regions linked to PM resistance derived from different genetic sources. The regions identified in this study are marked in red, while those previously identified from TGR1551 are in green. Candidate genes proposed for other resistance sources are also indicated. Physical positions refer to version v.4.0 of the Cucumis melo genome, available on the Melonomics database (Accessed on 1 June, 2022) (Adapted from López-Martín et al., 2022) 6.2 Case studies of successful gene cloning in Cucurbitaceae In Cucurbitaceae, the Mildew Locus O (MLO) gene family has been identified as a significant factor in PM susceptibility. Through genomic analysis, researchers have identified multiple MLOhomologs in species such as melon, watermelon, and zucchini, providing a comprehensive overview of this gene family's structure and evolution (Figure 5) (Iovieno et al., 2015). Another case study involves the identification of a novel candidate gene, CmoAP2/ERF, in pumpkin, which has been implicated in resistance to PM through a genome-wide association study (GWAS). This gene's allelic variation has been validated as a key factor in resistance, and a polymorphic marker has been developed for breeding purposes (Figure 6) (Alavilli et al., 2022). The exploration of allelic variation in the CmoAP2/ERF gene between PM resistant and susceptible lines as detailed in the research by Alavilli et al. (2022) is a significant step forward in understanding plant defense mechanisms at the genetic level. By pinpointing specific missense mutations and nucleotide changes that differentiate resistant from susceptible phenotypes, this research offers potential molecular markers for breeding programs aimed at enhancing disease resistance. This approach not only aids in the precise manipulation of plant genomes for improved traits but also contributes to the broader understanding of the functional dynamics of stress response genes in plants. Such detailed genetic insights are crucial for advancing plant breeding strategies, particularly in the context of increasing crop resilience to diseases amidst changing global climate conditions. 6.3 Challenges and advancements in cloning resistance genes Despite the progress made in cloning resistance genes, challenges remain. One of the main difficulties is the complexity of plant-pathogen interactions and the genetic diversity of both the host plants and the pathogens. However, advancements continue to be made, such as the overexpression of the Cucurbita moschata CmSGT1 gene in Nicotiana benthamiana, which resulted in increased resistance to PM. This study not only provided valuable genetic information for breeding disease-resistant pumpkin varieties but also contributed to understanding the molecular mechanisms underlying the functions of resistance genes (Guo et al., 2019).
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