*Pathogenesis-Related Proteins and Their Transgenic Expression for Developing Disease-Resistant… DOI: http://dx.doi.org/10.5772/intechopen.106774*


*Example of transgenic plants over-expressing PR proteins against plant pathogens.*

**Table 2.**

*Pathogenesis-Related Proteins and Their Transgenic Expression for Developing Disease-Resistant… DOI: http://dx.doi.org/10.5772/intechopen.106774*

### **7. Transgenic plants expressing antifungal activities**

Fungi are one of the most harmful phytopathogens, resulting in considerable production losses in most agricultural crops [119]. PR proteins have proven effective in preventing fungal diseases in plants as many of these targets or hydrolyze fungal cell walls, resulting in cell death. PR1, PR2, PR3, PR4, PR5, PR8, PR11, PR12, and PR13 have been identified as plants' most effective antifungal proteins. Transgenic approaches using PR proteins are suitable for developing long-lasting fungal pathogenresistant crops [64]. Of the various antifungal PR proteins, glucanases and chitinases are most widely used in transgenic technology to provide resistance against fungus.

The transgenic over-expression of glucanase and chitinase genes from different sources has been shown to be effective against pathogens, specifically fungus. It has been reported that overexpression of the tobacco glucanase gene imparted groundnut resistance to *Cercospora arachidicola* and *Aspergillus flavus*, demonstrating that fungal resistance is conferred via *in planta* transformation [120]. Transgenic Arabidopsis plants expressing grapevine *b-1,3-glucanase* (*VvGHF17*) confers resistance to *Colletotrichum higginsianum* and *Botrytis cinerea* [121]. Furthermore, tea with transgenic overexpression of the endo-*1,3-D-glucanase* gene, which expresses a potato glucanase, significantly improved tolerance to the blister blight fungus *Exobasidium vexans* [122]. Recently, oil palm resistance to *G. boninense* was improved by transgenic overexpression of *M. sativa* glucanase (*AGLU1*) [123]. Likewise, transgenic expression of chitinase genes have been reported to be antifungal generated transgenic zoysia grass was generated which overexpressed *Zjchi2* via *Agrobacterium-mediated* transformation and hence showed disease resistance against *Rhizoctonia solani* [124]. Currently, the overexpression of *LcCHI2* gene was identified that increasing the chitinase activity in transgenic tobacco and maize, resulting in improved resistance *to Pseudomonas tabaci*, *Alternaria alternata*, *Exserohilum turcicum*, *Curvularia lunata* [80].

Some other antifungal PR proteins that have been reported to be used in transgenics are thaumatin-like/osmotin-like proteins, defensin-like proteins, thionin, oxalate oxidase and lipid transfer protein. In fungal cells, thaumatin-like proteins are known to form transmembrane pores, whereas osmotin proteins are known to maintain the osmolarity of suitable solutes in cellular compartments [88]. In Arabidopsis thaliana, overexpression of the *TLP29* gene from grape *VqTLP29* improved resistance to powdery mildew and the bacteria *Pseudomonas syringae* [125]. Under *in vitro* conditions, transgenic poplars overexpressing *PeTLP* thaumatin genes showed enhanced resistance to *Marssonina brunnea* [126]. Similarly, in potatoes, overexpression of the osmotin gene (*OsmWS*) conferred resistance to the early blight fungus *A. solani* [88]. Many more transgenic plants have been generated that show increased resistance to phytopathogenic fungi by expressing the TLPs and OLPs as listed in **Table 2**.

The successful developed and characterized transgenic peanut and tobacco plants which overexpress the mustard *defenisn* gene and *Raphanus sativa*, *RsAFP2* gene for fungal resistance respectively [127]. The late leaf spot diseases *Cercospora arachidicola* and *Pheaoisariopsis personata* were more resistant to transgenic peanut plants whereas, *Phytophthora parasitica* pv. nicotianae and *Fusarium moniliforme* resistance was higher in transgenic tobacco plants. Similarly, the *rDrr230a* defensin protein gene suppressed spore germination and growth of both *Fusarium tucumaniae* and *Colletotrichum gossypii* var. cephalosporioides in transgenic *Pichia pastoris* [128]. The antifungal thionin genes (*AT1G12660* and *AT1G12663*) from *A. thaliana* had been used to produce transgenic potato conferring resistance against pathogenic fungi such as *Fusarium solani* and *Fusarium oxysporum* [104]. Furthermore, the overexpression of thionin increased canker resistance and decreased canker bacterial development when transgenic Carrizo plants expressing the modified plant thionin were produced by *Agrobacterium-mediated* transformation [129]. Peanuts with transgenic expression of the oxalate oxidase expressing gene were more resistant to *Sclerotinia* blight [130]. Also, overexpression of oxalate oxidase genes has been developed to increase resistance against *Sclerotinia sclerotiorum* in transgenic Glycine max [108].

Transgenic expression of LTPs has been shown to improve resistance to phytopathogenic fungi in some studies. As an example, antimicrobial protein gene (*Ace-AMP1*) isolated from *Allium cepa* has been overexpressed in both *Triticum aestivum* and *Oryza sativa* through *Agrobacterium-mediated* transformation, microprojectile bombardment, in *planta* assays, conferring resistance against *Sphaerotheca pannosa* var. rosae [113], *Magnaporthe grisea*, *Rhizoctonia solani* and *Xanthomonas oryzae* [116] respectively. Recently, *A. thaliana* LTP overexpressing transgenics has been shown to increase resistance toward pathogens *Plasmodiophora brassicae* and *F. graminearum* [112, 131]. Some other examples of successfully generated transgenic plants with enhanced production of hydrolytic enzymes and resistance against phytopathogenic fungi are given in **Table 2**.

### **8. Transgenic plant expressing bacterial resistance**

Numerous bacterial pathogens causing massive yield losses have been isolated and identified from different agriculturally important crops. Pathogenesis-related proteins are well-known weapons to combat resistance against these bacterial pathogens. Many in-vitro studies have shown the antibacterial properties of many PR proteins *viz* PR10 (Ribonuclease-like proteins), PR12 (defensins), PR13 (thionins) and PR14 (Lipid-transfer protein) [90, 116, 132]. Among these, PR10 shows broad spectrum of antibacterial activity against *P. syringae*, *Agrobacterium tumefaciens*, *A. radiobacter*, *Pseudomonas aureofaciens* and *Serratia marcescens* [90, 133]. Overexpression of lipid transfer protein (PR14) in rice plants showed increased resistance to bacterial as well as fungal pathogens (**Table 2**) [116]. The antibacterial efficacy of additional PR proteins and AMPs against a variety of bacterial diseases in economically significant crops has to be further investigated.

### **9. Transgenic plant expressing insect resistance**

Plants expressing PR genes have been engineered in several experiments, resulting in enhanced pest resistance. The expression of both low and high levels of *MTI-2* was reported by using *Agrobacterium* transformation technique in tobacco and *Arabidopsis* plants leading to resistance against *Spodoptera littoralis* [134]. The wound-inducible expression of a *Bacillus thuringiensis* endotoxin gene which directed significant insecticidal gene expression to protect transgenic rice from *Chilo suppressalis* Walker [94]. Transgenic rice plants were developed by particle bombardment or *Agrobacterium-mediated* transformation of *mpi* gene leading to resistance against *C*. *suppressalis* (**Table 2**) [93].
