Tree Genetics and Molecular Breeding 2024, Vol.14, No.3, 119-131 http://genbreedpublisher.com/index.php/tgmb 122 observed in Cryptomeria fortunei, where CfICE1 enhances cold, drought, and salt resistance by regulating the CBF (C-repeat binding factor) gene pathway (Zhu et al., 2022). Furthermore, the expression of genes such as MaPIP2-7 and WRKY8 in different species underscores the shared molecular pathways in stress resistance, albeit with variations in gene expression levels and specific physiological responses. The identification of such genes across diverse tree species offers valuable insights into the universal and adaptive mechanisms that trees have evolved to survive under adverse environmental conditions. 4 Case Studies: Successful Identification and Application of Stress Resistance Genes 4.1 Detailed examination of specific gene identification studies A notable example of successful gene identification is the work done on the tree species Dalbergia sissoo, where researchers identified resistance gene analogs (RGAs) of the NBS-LRR family through transcriptome analysis. This study utilized advanced molecular and bioinformatics techniques to identify and characterize genes involved in resistance to dieback disease, a major threat to this species (Ijaz et al., 2022). Similarly, the identification of candidate genes in Populus trichocarpa through genome-wide association studies (GWAS) and QTL mapping has significantly contributed to understanding the genetic basis of disease resistance in this species (Younessi-Hamzekhanlu and Gailing, 2022). Another critical study focused on Casuarina equisetifolia, a stress-tolerant forest species, where researchers assembled the genome to identify genes associated with secondary growth and stress tolerance. This high-quality genome assembly provided valuable insights into the molecular mechanisms underlying the tree's resilience to environmental stressors such as typhoons and drought (Ye et al., 2019). 4.2 Implementation of identified genes in breeding programs The successful identification of stress resistance genes has paved the way for their implementation in breeding programs aimed at developing more resilient tree species. For instance, the integration of gene markers identified through GWAS and QTL mapping into marker-assisted selection (MAS) has significantly accelerated the breeding of disease-resistant forest trees. This approach allows for the selection of elite genotypes with enhanced resistance, thereby reducing the breeding cycle time and improving the efficiency of breeding programs (Figure 2) (Younessi-Hamzekhanlu and Gailing, 2022). Figure 2 Perception of pathogens by trees, various signaling pathways, and corresponding defense mechanisms (Adapted from Younessi-Hamzekhanlu and Gailing, 2022) Image caption: The figure illustrates how pattern recognition receptors (PRRs) and nucleotide-binding leucine-rich repeat receptors (NBS-LRRs) recognize pathogen-associated molecular patterns (PAMPs) and effectors, initiating PAMP-triggered immunity (PTI) and effector-triggered immunity (ETI). Additionally, the figure shows the downstream responses triggered by these signals, including the production of reactive oxygen species (ROS), activation of calcium signaling pathways, kinase cascade reactions, and the roles of plant hormones such as jasmonic acid and salicylic acid in disease resistance. These signaling pathways work together to enhance the resistance of trees to pathogens (Adapted from Younessi-Hamzekhanlu and Gailing, 2022)
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