In Silico Genome-wide Identification and Expression Analysis of the Pin-2 Serine Protease Inhibitor Gene Family in Eggplant (Solanum melongena L.)

Serine protease inhibitors (SPIs) are ubiquitously distributed and structurally well-conserved proteins that interfere with serine protease catalysis and function as intrinsic defense molecules for plants. Potato inhibitor type II (Pin-II) SPIs found mainly in Solanaceous species are important in minimizing injury caused by pathogen infection and insect herbivory. Eggplant (Solanum melongena L.), an important vegetable crop, is severely damaged by insect pests and diseases. Multiple Pin-II SPI proteins had been identified in tomato, potato, tobacco, and pepper, with only one in eggplant. This study conducted a bioinformatics analysis and identified 15 Pin-2SPI genes in cultivated eggplant, herein named as SmePin-2SPI.1 to SmePin-2SPI.15. Phylogenetic and syntenic analyses confirmed the homology of these genes with Pin-II SPIs from other Solanaceae and non-Solanaceae plant species based on the conserved protease inhibitor 2 (PF02428; Prot-Inhib 2) domains and coding regions, indicating conservation within the Solanaceae. Functional annotation indicates that these genes are involved in the negative regulation of serine peptidase activity and plant defense. Major cis-acting regulatory elements are associated with plant hormones and stress responses. An in-silico analysis of transcriptomic profiles for constitutive and induced expression indicates that SmePin-2SPI genes are highly expressed in reproductive organs and exhibit strong reactions to biotic stress, particularly bacterial wilt infection. SmePin-2SPI.1 is highly expressed in most plant organs and shows differential expression in response to various stress treatments. This study also demonstrated sequence homology of Pin-2SPI genes using PCR amplification for three species of eggplant within the Solanum clade, the cultivated species S. melongena, S. aethiopicum, and the wild species S. mammosum. These initial findings provide insights on the diversity of the Pin-II SPI gene family in eggplants, as well as their potential role in plant defense. [ABSTRACT FROM AUTHOR]