Molecular Pathogens 2024, Vol.15, No.1, 30-39 http://microbescipublisher.com/index.php/mp 31 fungal pathogens is Colletotrichum camelliae, which causes tea anthracnose, a disease that affects mature leaves and reduces both yield and quality. The cerato-platanin protein CcCp1 from C. camelliae plays a key role in fungal pathogenicity. Mutants lacking CcCp1 lose virulence and have a reduced ability to produce conidia, indicating the importance of this protein in the disease process. Additionally, the accumulation of jasmonic acid in susceptible tea cultivars upon infection suggests its role in regulating fungal infection (Liu et al., 2023b). Another significant fungal pathogen is Pestalotiopsis theae, responsible for tea gray blight disease. Resistance to this pathogen has been linked to specific metabolites such as phenolic acids and flavonoids, which are more abundant in resistant tea plant resources. The presence of certain bacterial and fungal genera also correlates with resistance, highlighting the complex interplay between the tea plant's microbiome and its defense mechanisms (Zhang et al., 2022). Furthermore, the mycovirus Pestalotiopsis theae chrysovirus-1 (PtCV1) has been shown to modulate the pathogenic traits of P. theae, converting it from a virulent pathogen to a non-pathogenic endophyte, thereby providing an alternative approach to biological control (Zhou et al., 2021). 2.2 Bacterial pathogens Bacterial pathogens also pose a significant threat to tea plants. The interaction between plants and bacterial pathogens involves complex genetic and molecular mechanisms. Plants have evolved resistance genes (R genes) that encode proteins capable of recognizing pathogen-derived molecules and triggering defense responses. These responses include the hypersensitive response (HR), which involves rapid tissue necrosis at the infection site to limit pathogen spread. The genetic basis of plant resistance to bacterial pathogens can be both qualitative and quantitative, involving major and minor genes, respectively (Zhang et al., 2013). 2.3 Viral pathogens Viral pathogens are less common but can still cause significant damage to tea plants. Plants have developed sophisticated defense mechanisms to combat viral infections, including RNA silencing pathways that target and degrade viral nucleic acids. Resistance genes also play a crucial role in recognizing viral pathogens and initiating defense responses. The cellular and physiological features associated with these responses have been well characterized, providing insights into the mechanisms of plant resistance to viruses (Kourelis and Hoorn, 2018). 2.4 Other significant pathogens In addition to fungi, bacteria, and viruses, other significant pathogens can affect tea plants. For instance, the fungal pathogen Exobasidium vexans causes blister blight, a disease that can lead to substantial crop losses. Transgenic tea plants overexpressing a class I chitinase gene from potato have shown enhanced resistance to this pathogen, demonstrating the potential of genetic engineering in improving disease resistance in tea plants (Singh et al., 2015). 3 Genetic Basis of Disease Resistance 3.1 Resistance (R) genes in tea plants Resistance (R) genes play a crucial role in the defense mechanisms of tea plants against various pathogens. These genes encode proteins that can recognize specific pathogen-derived molecules and trigger defense responses. The majority of R genes encode either cell surface or intracellular receptors, which are involved in the direct or indirect perception of pathogen molecules (Figure 1) (Kourelis et al., 2018). The structural features of R genes, such as nucleotide-binding sites and leucine-rich repeats, are conserved across different plant species and are essential for their function (Sekhwal et al., 2015). The evolution of Rgenes is driven by mechanisms such as gene duplications, recombination, and diversifying selection, which contribute to their diversity and ability to recognize a wide range of pathogens. The first cloned Rgenewas Hm1 from maize, which encodes an enzyme that detoxifies HC toxin produced by the fungal pathogen Cochliobolus carbonum. Over the years, several models of Rgene function have been proposed, including the guard model, the decoy model, and the NLR-ID model. R proteins use nine different mechanisms to
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