Molecular Pathogens, 2025, Vol.16, No.2, 77-86 http://microbescipublisher.com/index.php/mp 79 Another common disease is called grey mold, which is caused by Botrytis cinerea. This pathogen exploits changes in grapes during ripening to attack. It will activate some genes related to cell death to help yourself get infected. Grapes will also fight back, such as activate some defense pathways, such as salicylic acid pathways and resveratrol synthesis. Studies have shown that if grapes can activate these defensive responses early, they can prevent the spread of bacteria (Kelloniemi et al., 2015; Haile et al., 2017). 2.2 Viral pathogens In grapevine leafroll-associated virus (GLRaV), especially GLRaV-2, is a virus that is harmful to grapes. This virus inhibits the grape's defense response. It contains a protein called p24, which can bind to grape transcription factor VvRAV1, which prevents it from deactivating disease-resistant genes. In this way, the immune capacity of plants is reduced, and viruses are more likely to accumulate in the plants and cause diseases (Zhang et al., 2022). 2.3 Bacterial pathogens There is a bacteria called Xylella fastidiosa that causes Pierce disease in grapes. The way vine defends against it is to increase the number of certain enzymes, such as chitinase and β-1,3-glucanase. These enzymes can help plants fight pathogenic bacteria (Chakraborty et al., 2016). There is also a common bacteria called Agrobacterium tumefaciens, which can cause root gall disease in grapes. Plants usually defend against such bacteria in two ways: one is to activate systemic immune responses, and the other is to produce some compounds that are lethal to bacteria. 3 Molecular Basis of Grapevine Defense 3.1 Role of pathogen recognition receptors (PRRs) in initial defense When the vine first encountered a pathogen, it relied on a type of molecule called "pathogen recognition receptor (PRR). They can identify signals from bacteria or microorganisms, such as proteins, glycolipids and polysaccharides. This step is the first step to initiating a defensive response (Heloir et al., 2019). For example, there is a receptor kinase called LysM in grapes, where VvLYK1-1 and VvLYK1-2 can recognize chitin of fungi. When they find chitin, defense mechanisms are triggered (Brulé et al., 2018). In addition, cyclic lipopeptides released by beneficial microorganisms such as Bacillus subtilis can also be sensed by grapes. This perception will also allow the grapes to initiate an innate immune response. 3.2 Signal transduction pathways in defense response When PRR successfully recognizes the bacteria, a series of signaling reactions will be initiated in the grape body. These signal channels are like messengers, quickly spreading the news of "the enemy is coming" to various places. In this process, many signal molecules are used, such as reactive oxygen species (ROS) and some phytohormones, such as salicylic acid (SA) and jasmonic acid (JA). These substances can help grapes activate defense responses. Studies have found that the transcription factor VvWRKY33 is part of this process, which activates responses to Axonium grapezoids (Merz et al., 2015). Also, the recognition of cyclic lipopeptides will also trigger different pathways. For example, anti-mold subtilisin can enable the SA and JA pathways simultaneously, while surfactants mainly affect the SA pathway (Farace et al., 2015). The earlier these signals are activated, the better the defenses of the plants are usually (Figueiredo et al., 2022). 3.3 Activation of defense-related genes If the vine wants to defeat the pathogen, it will eventually rely on starting a batch of disease-resistant genes. This process is like mobilizing the “defense army” to fight. There are two transcription factors - VviWRKY10 and VviWRKY30, one mainly regulates the genes associated with salicylic acid and the other regulates the ethylene pathway. These two pathways can work together to effectively fight powdery mildew (Zhou et al., 2024). There are also two important disease-resistant gene loci - RUN1 and REN1, which activate genes such as VvSTS36 and VvPEN1. These genes can help grapes produce reactive oxygen species and can also cause programmed cell death, thereby preventing bacteria from spreading (Zhang et al., 2019). In general, the timely activation of these genes is a key step in whether the vines can successfully defend against pathogens.
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