Tree Genetics and Molecular Breeding 2024, Vol.14, No.2, 57-68 http://genbreedpublisher.com/index.php/tgmb 62 species provides potential targets for gene editing to enhance cold resistance (Yousefi et al., 2022). The use of CRISPR/Cas9 to develop molecular markers for breeding cold-resistant tree varieties is a significant innovation in this field. Moreover, the overexpression of genes involved in stress sensing and signaling, such as those in the abscisic acid core pathway, has been shown to generally enhance drought and salt stress tolerance, which could be applied to cold stress as well (Polle et al., 2019). These biotechnological approaches aim to recruit a suite of defense systems to improve cold resistance in trees, although field studies are necessary to validate their effectiveness under natural conditions. 6 Case Studies: Integrative Genetic Studies on Tree Stress Resistance Recent integrative genetic studies have provided significant insights into the mechanisms underlying tree stress resistance. For instance, a meta-analysis of RNA-Seq samples from various fruit tree species identified key genes involved in drought and salinity tolerance. This study highlighted the conserved role of 750 genes in salinity resistance and 683 genes in drought resistance, with 82 genes commonly regulated under both stresses. The findings emphasized the importance of pathways related to defense response, drug transmembrane transport, and metal ion binding, as well as hormonal cROSstalk in stress responses (Benny et al., 2020). Another study focused on the WRKY transcription factor WRKY8 in tomatoes, demonstrating its role in enhancing resistance to pathogen infection and tolerance to drought and salt stresses through the regulation of stress-responsive genes and antioxidant enzyme activities (Gao et al., 2019). 6.1 Comprehensive analysis of multi-stress resistant varieties Comprehensive analyses of multi-stress resistant varieties have revealed the complex interplay of genetic factors that confer resistance to multiple abiotic stresses (Table 1). For example, a study on cotton identified key regulatory hub genes involved in drought and salt stress tolerance, such as NSP2, DRE1D, and ERF61, which are associated with significant differential expression in response to these stresses (Bano et al., 2022). Similarly, research on Populus euphratica identified a calcium-dependent protein kinase gene, PeCPK10, which enhances both drought and cold stress tolerance by promoting stomatal closure and upregulating stress-responsive genes (Chen et al., 2013). These studies underscore the potential of leveraging multi-stress resistant genes to develop robust tree varieties. Table 1 Classification of the genomic architecture of resistance to biotic stress in tree species Species Location of mapping population Genetic markers Number of associated genetic markers Genomic architecture Quercus robur France (bouran y champenoux) SNPs 2 regions, 165 and 196 genes, respectively Polygenic Eucalyptus globulus Tasmania AFLPs y SSRs 2QTLs Mendelian Eucalyptus grandis × Eucalyptus urophylla Brazil SNPs 1 gen with 218 SNPs Mendelian Eucalyptus grandis Brazil RAPDs & 1 gen 6 markers, 1 gen Mendelian Picea abies Finland SNPs 10 SNPs in 8 genes Mendelian Pinus lambertiana North America SNPs 4 SNPs in 3 genes Polygenic Populus trichocarpa NA SNPs NA Polygenic Populus deltoides North Central United States RAPDs (OPG10 340 y OPZ19 1800) NA Polygenic Hevea spp. South America Kruskal-Wallis marker 6QTLs Polygenic Eucalyptus NA SSRs, AFLPs, RAPDs, RFLPs, SNPs 1gen Mendelian Populus deltoides × Populus trichocarpa Europe RFLPs, RAPDs, AFLPs, STS, SSRs NA Polygenic
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