*2.2. Plant Proteins and Peptides with Insecticidal and Fungitoxic Properties*

Insect pests and phytopathogenic fungi are detrimental to several crops and cause significant economic losses in agriculture worldwide. To cope with herbivory and fungal diseases, plants have evolved sophisticated defense mechanisms. Plant tissues accumulate, constitutively or after induction, various classes of defensive compounds that confer resistance against herbivores and infection by fungi, bacteria, viruses, as well as nematodes. The most known plant proteins involved in defense mechanisms against insect pests include lectins [22], ribosome-inactivating proteins of types 1 and 2 [23], inhibitors of proteolytic enzymes and glycohydrolases [24], modified forms of storage proteins [25,26], among others. Several plant peptides display antifungal properties such as defensins [27], lipid transport proteins [28], chitinases [29], lectins [30], thionins [31], cyclopeptide alkaloids [32] and other less common types. For a general review on these topics please refer to Dang and Van Damme [33] and Grossi-De-Sá et al. [21].

Ureases represent another group of plant proteins with insecticidal and antifungal properties which widen the proposed physiological roles of these enzymes [34–37]. Ureases (urea amidohydrolase; EC 3.5.1.5) are well conserved and nickel-dependent enzymes that catalyze urea hydrolysis into ammonia and carbon dioxide, synthesized by plants, fungi and bacteria [38–41]. Canatoxin is a less abundant urease isoform isolated from *Canavalia ensiformis* (jack bean) seeds [42,43]. Structurally similar to the seed's major urease, both proteins display insecticidal and antifungal properties independent of their ureolytic activity [35,38,39]. Soybean (*Glycine max*) and pigeon pea (*Cajanus cajan*) ureases were also shown to display insecticidal [44–46] and antifungal [44,47,48] properties. Noteworthy, ureases are insecticidal against hemipteran pests (such as the stink bug *Nezara viridula* and the cotton stainer bug *Dysdercus peruvianus*), which were not susceptible to the entomotoxic activity of Cry toxins from *B. thuringiensis* [18,19]. Since these proteins are abundant in many edible vegetables, particularly in legumes, they can be generally regarded as biosafe [49].
