## 5 Application of PGIP in Plant Disease Resistance Genetic Engineering  
The PGIP anti-disease effect has been confirmed in a series of in vivo experiments. PGIP-mediated fungi resistance has been shown in various important cash crops, such as grapes [57; 58], papaya [59], potatoes [51], alfalfa [15], cotton [60], green beans [6; 28; 61], tomatoes [62], peas [63], mandarin orange [64], tobacco [65], and Arabidopsis [66]. PGIP expression does not affect plant phenotype or inhibit plant growth in sugar beet [67] or tobacco [67]. Thus, PGIP should be able to be used to improve plant disease resistance by overexpressing active PGIPs or by strengthening the specific recognition and inhibitory effect of native PGIPs by altering amino acid residues at recognition sites [68]. Consistently, the overexpression of _GhPGIP1_ enhanced the resistance of cotton (_Gossypium hirsutum_ L.) to Verticillium and Fusarium wills, and resistance was severely reduced when the gene was silenced [60]. The overexpression of _HpPGIP_ led to the upregulation of key genes involved in hormone signaling, microRNA-based gene silencing, homeostasis of reactive oxygen species, and the phenylpropanol pathway [20]. There were increased expression levels of disease resistance-related genes, including _VvPGIP_ in fruit inoculated with _B. cinerea_ infection [47]. \begin{table}
\begin{tabular}{c c c c c} \hline \hline  & **Gene** & **System for Expression** & **Mediated Factor** & **Enhanced Resistance** \\ \hline Grape & & & Auxin, salicylic acid and sugar & \\ (_Vitis vinifera_ L.) & _VvPGIP1_ & Tobacco & treatment, wounding, and & _Botrytis cinerea_ \\  & & & pathogen infection [46; 47] & \\  & _GmPGIP1_ & PVX/_Nicotiana_ & PVX/Nicotiana benthamiana_ & [48] \\ Soybean & _GmPGIP2_ & & _bethamiana_ & [31] \\ (_Glycine max_ L.) & _GmPGIP3_ & PVX/_Nicotiana_ & PVX/_Nicotiana benthamiana_ & _Botrytis cinerea, Botrytis_ \\  & _GmPGIP4_ & & & _aclada_[31; 49] \\  & _GmPGIP7_ & & & [31] \\ Potato leaves (_Solanum_ & & & Salicylic acid, wounding, and & [50] \\ _tuberosum_ L. cv. _Spunta_) & & & infection & _Phytophthora infestans_[51] \\ Kiwifruit (_Actinidia_ & & & _Botrytis cinerea_ infection [41] & _Botrytis cinerea_[52] \\  & Strawberry & & & \\ (_Fragaria \(\times\) ananassa_ & _PGIP_ & _B. cinerea or wounding_ & _Botrytis cinerea_ wounding [38] \\  & Duch.) & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Cont. _PvPGIP_ exhibits strong inhibition toward most PGs from different pathogens [69]. _PvPGIP2_ can be transferred to _Brassica napus_ via _Agrobacteriumtium_, and in vitro experiments show that crude extract from transgenic strains can inhibit 29-37% PG activity in rhizoctonia, with an increased effect seen with the progression of infection and delayed lesion expansion in the transgenic strain [70]. [PERSON] et al. [71] overexpressed soybean GmPGIP3 in wheat and found the transgenic strain exhibited elevated resistance to wheat root rot. The overexpression of _OsPGIP1_ that can inhibit the PG from sheath blight allowed rice to efficiently limit the expansion of _R Rhizoctonia solani_, with no effect on agronomic characteristics [19; 72; 73]. Similarly, the expression of _PGIP1_ from cotton in _Arabidopsis_ strengthened its resistance to fungal disease caused by _Verticillium dahliae_ and _Fusarium_, and silencing _PGIP1_ in cotton increased its sensitivity to these fungi [60]. _AcPGIP_ silencing enhanced kiwifruit's susceptibility to _B. cinerea_[52]. The expression of PGIP from sugar beet (_BvPGIP1_) can protect transgenic tobacco against _R Rhizoctonia solani_, _Fusarium_, and _Botrytis cinerea_[24]. The overexpression of _OsPGIP2_ can efficiently inhibit _Sclerotinia_ disease and enhance resistance to _Sclerotinia_ in _Brassica napus_[74]. Overall, many studies show that increasing the protein levels of PGIPs can allow plants to effectively resist many common pathogenic fungi [75] (Table 2). PGIPS can also inhibit bacterial diseases in different crops [45; 73; 78; 83] (Table 3).