**1. Introduction**

Plants being sessile organisms are exposed to a number of stresses. External environmental fluctuations, different insect pest and pathogen considerably affect the growth, development, yield and quality [1]. To safe guard themselves against these threats, plants have evolved some sophisticated defense mechanisms. The inducible defense responses of plants include synthesis of signaling molecules, such as methyl jasmonate (MeJA), salicylic acid (SA) and ethylene (ET), which work in a complex network interaction that in turn regulates the expression of defense related genes (PR) and molecules such as reactive oxygen species (ROS), phytoalexins, proline, phenylpropanoids and pathogenesis-related genes [2,3]. Earlier studies revealed the significant role of these (PR) proteins in plant defense system [4,5]. During the biotic threat, plant defense mechanism consists of two typical interconnecting layers to develop plant immune system designated as effector-triggered immunity (ETI) and pattern-triggered immunity (PTI), thus participating in signal transduction [6,7]. A set of pathogenesis related (*PR-2* and *PR-5*) genes are involved in PTI and ETI, depending on the magnitude and time of the interacting signaling components [8,9].

Chitin-binding proteins (CBP), encoded by chitin-gene family, are PR proteins, which enhance resistance to different stresses in several crop plants [10–14]. These CBP proteins consist of one or several chitin-binding domains with high affinity and have a range of numerous complex glycoconjugates covering GlcNAc or *N*-acetyl-D-neuraminic acid (NeuNAc) as building blocks. Thus far, the chitinase responsible genes have been classified into seven different classes (classes I–VII) as they belongs to the glycoside\_hydrolase\_families, thus signifying that the chitinase isozymes were encoded by a family of multi-genes [4,15]. Some members of class I chitinases are localized in the vacuole, whereas other chitinases, such as the class III chitinases are positioned outside the cell [4]. Plant chitinases are responsible for the catalysis of chitin, the second most abundant polysaccharide after cellulose. Chitin is the part of the cell walls in most of fungi as well as in plants. Plant chitinases also have shown resistance to several pathogens, such as bacteria, viruses, and some abiotic stresses [16]. Certain chitinases are reported to take part in various physiological processes of plants, such as ethylene synthesis and embryogenesis [17]. CBPs are constitutively present in plant leaves, stems, seeds, flowers, and tubers. They are developmentally and tissue-specifically regulated [18,19]. Up to date, chitin genes have been cloned and characterized in numerous plants species, including *Arabidopsis thaliana* [20], *Triticum aestivum* [15], *Oryza sativa* [21], *Zea mays* [4] and *Sorghum bicolor* [22]. A class I chitin-binding proteins was isolated from *Hordeum vulgare* and has been shown antifungal activity [23]. The pathogen-inducible acidic class III chitinase proteins were isolated from *Nicotiana tobacum* after the infection of tobacco mosaic virus (TMV) [5] while endo-chitinase from *Trichoderma harzianum* showed higher resistance against phytopathogenic fungi in tobacco and apple [24,25].

Pepper (*Capsicum annuum* L.) is one of the essential Solanaceous vegetable crop possessing great economic value throughout the world. Its growth, yield and quality are reduced by numerous biotic factors such as bacterial wilt, *Phytophthora* blight, viral infections, insect pests and abiotic stresses (extreme temperatures, drought, salinity, and heavy metals) [26,27]. These stresses adversely affect the quality and yield of pepper plants. In response, plants have evolved some sophisticated defense mechanisms including oxidative burst and calluses into the cell wall and regulation of signaling networks to combat these stresses [7,28,29]. It has been reported that *Phytophthora capsici* infests pepper, eggplant, tomato, all cucurbits, and more recently snap and lima beans [30,31]. To control the attack of pathogen invasion in the host tissues, inducible biochemical reactions create a protective physiological condition [14].

The chitin-binding proteins are very important as they can enhance resistance against biotic and abiotic stress as well as in plant growth and development. The molecular function of chitin-binding protein genes in pepper plant are un-known. In the current study, sixteen chitin genes (CaChi) in pepper were mined through bioinformatics and their response to biotic and abiotic stresses and hormonal treatment were examined. Subsequently, the gene architecture, conserved domains, exon–intron structure, chromosomal location, gene duplication, gene ontology (GO) characterization, *cis-*acting regulatory elements in the promoter regions and phylogenetic relationships of the pepper chitin-binding protein were elucidated. This study provides a base for future research regarding pepper chitin-binding protein. Furthermore, differential expression was recorded against biotic (*Phytophthora capsici* two strains PC, HX-9) and abiotic (cold, drought, and salt) stress and hormonal treatment (SA,

MeJA, and ABA) along with tissue specific expression in different plant parts. This study provides a foundation for further characterization of CaChi members in pepper and valuable information regarding function of this significant gene family in other important crops as well.
