Field Crop 2024, Vol.7, No.6, 287-297 http://cropscipublisher.com/index.php/fc 292 network of signal transduction pathways. These mechanisms collectively enhance the plant's ability to withstand various environmental stresses. 5 Molecular Mechanisms of Stress Resistance 5.1 Gene regulation under stress conditions Gene regulation plays a pivotal role in the stress resistance of kiwifruit. Various genes are differentially expressed in response to environmental stresses such as drought, salinity, and cold. For instance, the R1R2R3-MYB transcription factor AcMYB3R has been shown to enhance drought and salinity tolerance in Arabidopsis thaliana by upregulating stress-responsive genes like RD29A, RD29B, COR15A, and RD22 (Zhang et al., 2019). Similarly, the expression of genes involved in carbohydrate and amino acid metabolism, as well as reactive oxygen species (ROS) scavenging, is significantly altered under waterlogging stress in Actinidia valvata (Li et al., 2022). These findings highlight the complex regulatory networks that enable kiwifruit to adapt to various abiotic stresses. 5.2 Role of transcription factors in stress tolerance Transcription factors (TFs) are crucial in modulating the expression of stress-responsive genes. The heat shock transcription factors (HSFs) in kiwifruit, particularly AeHSFA2b, have been identified to play a significant role in salt tolerance by binding to the promoter of stress-responsive genes and enhancing their expression (Ling et al., 2023). Additionally, the bZIP transcription factor AchnABF1 has been shown to improve cold tolerance by upregulating genes associated with ABA-dependent and ABA-independent pathways, thereby enhancing ROS-scavenging abilities (Jin et al., 2021). Another bZIP TF, AcePosF21, interacts with the R2R3-MYB TF AceMYB102 to regulate ascorbic acid biosynthesis, which is crucial for mitigating oxidative damage under cold stress (Liu et al., 2023). These TFs orchestrate a coordinated response to environmental stresses, thereby enhancing the resilience of kiwifruit. 5.3 Molecular breeding for enhanced stress resistance Molecular breeding techniques have been employed to enhance stress resistance in kiwifruit. Overexpression of specific genes, such as AcMYB3R and AeHSFA2b, in model plants like Arabidopsis thaliana has demonstrated significant improvements in drought, salinity, and cold tolerance (Zhang et al., 2019; Ling et al., 2023). Furthermore, the functional validation of candidate genes like betaine aldehyde dehydrogenase (AvBADH) from Actinidia valvata has shown improved salt tolerance in transgenic kiwifruit and Arabidopsis plants (Abid et al., 2022). These molecular breeding strategies provide valuable insights and tools for developing kiwifruit cultivars with enhanced stress resistance. 5.4 Advances in genomic and proteomic studies Recent advances in genomic and proteomic studies have provided deeper insights into the stress response mechanisms in kiwifruit. Genome-wide identification and analysis of gene families, such as the HSF and bZIP families, have revealed their roles in stress tolerance (Jin et al., 2021; Ling et al., 2023; Tu et al., 2023). Transcriptome and metabolome analyses have identified key regulatory networks and differentially expressed genes involved in stress responses, such as those related to glycine betaine, pyruvate metabolism, and ROS scavenging (Abid et al., 2022; Li et al., 2022). Additionally, the identification of cold-responsive gene modules, such as the AaCBF4-AaBAM3.1 module, has elucidated the molecular basis of freezing tolerance in kiwifruit (Sun et al., 2021). These studies provide a comprehensive understanding of the molecular mechanisms underlying stress resistance and pave the way for targeted breeding and genetic engineering approaches. By integrating findings from various studies, we can better understand the complex molecular mechanisms that enable kiwifruit to withstand environmental stresses, ultimately contributing to the development of more resilient cultivars. 6 Case Study: Resistance to Bacterial Canker in Kiwifruit 6.1 Overview of bacterial canker disease Bacterial canker, caused by Pseudomonas syringae pv. actinidiae (Psa), is a significant threat to the kiwifruit industry, leading to substantial economic losses globally. The disease was first identified in Japan in 1984 and has
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