Molecular Plant Breeding 2024, Vol.15, No.2, 70-80 http://genbreedpublisher.com/index.php/mpb 72 3 Applications in Tree Breeding 3.1 Improving disease resistance 3.1.1 Case studies of disease resistance improvement Genome editing technologies, particularly CRISPR/Cas9, have been successfully applied to enhance disease resistance in various plant species. For instance, the development of disease-resistant crops through precise genome modifications has been demonstrated in several studies. These modifications include the introduction of resistance genes or the alteration of susceptibility genes to confer resistance against bacterial, fungal, and viral pathogens (Nerkar et al., 2022). Specific case studies have shown that editing genes related to disease resistance can significantly reduce the impact of diseases on crop yield and quality, thereby contributing to sustainable agriculture (Yin and Qiu, 2019). 3.1.2 Mechanisms of resistance gene editing The mechanisms underlying resistance gene editing involve the precise modification of target genes to enhance their resistance properties. CRISPR/Cas9 and its variants, such as base editors and prime editors, enable targeted nucleotide substitutions and precise gene corrections without the need for double-stranded breaks or donor DNA templates (Figure 1) (Hua et al., 2021; Molla et al., 2021). These tools can be used to knock out susceptibility genes or introduce beneficial mutations that enhance the plant's innate immune response, thereby improving disease resistance (Chen et al., 2019; Abdelrahman et al., 2021). Figure 1 The architecture of base editors (Adopted from Hua et al., 2021) Image caption: Panel A depicts the cytosine base editor (CBE), which uses an SpCas9 (D10A) nickase fused with a cytidine deaminase and a uracil glycosylase inhibitor (UGI) to convert cytosine (C) to uracil (U), leading to a C to T transition upon DNA replication; Panel B shows the adenine base editor (ABE), which employs an evolved adenosine deaminase to convert adenine (A) to inosine (I), resulting in an A to G transition; Panel C presents the DddAtox-derived cytosine base editor, which is designed for targeting plant organelles like mitochondria and chloroplasts, highlighting the versatility and specificity of these gene-editing tools in various cellular contexts (Adapted from Hua et al., 2021) 3.2 Enhancing growth and yield 3.2.1 Genetic modifications for faster growth Genome editing technologies have been employed to enhance the growth rate of trees by targeting genes involved in growth regulation. For example, modifications in genes that control hormone pathways or cell division can lead to faster growth and increased biomass production (Chen et al., 2019; Nerkar et al., 2022). These genetic modifications are achieved through precise edits that optimize the expression of growth-related genes, resulting in trees that grow more rapidly and efficiently (Hahne et al., 2019).
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