Evolutionary Conservation and Expression Patterns of Neutral/Alkaline Invertases in Solanum

The invertase gene family in plants is composed of two subfamilies of enzymes, namely, acid- and neutral/alkaline invertases (cytosolic invertase, CIN). Both can irreversibly cleave sucrose into fructose and glucose, which are thought to play key roles in carbon metabolism and plant growth. CINs are widely found in plants, but little is reported about this family. In this paper, a comparative genomic approach was used to analyze the CIN gene family in Solanum, including Solanum tuberosum, Solanum lycopersicum, Solanum pennellii, Solanum pimpinellifolium, and Solanum melongena. A total of 40 CINs were identified in five Solanum plants, and sequence features, phylogenetic relationships, motif compositions, gene structure, collinear relationship, and expression profile were further analyzed. Sequence analysis revealed a remarkable conservation of CINs in sequence length, gene number, and molecular weight. The previously verified four amino acid residues (D188, E414, Arg430, and Ser547) were also observed in 39 out of 40 CINs in our study, showing to be deeply conserved. The CIN gene family could be distinguished into groups alpha and beta, and alpha is further subdivided into subgroups alpha 1 and alpha 2 in our phylogenetic tree. More remarkably, each species has an average of four CINs in the alpha and beta groups. Marked interspecies conservation and collinearity of CINs were also further revealed by chromosome mapping. Exon-intron configuration and conserved motifs were consistent in each of these alpha and beta groups on the basis of in silico analysis. Expression analysis indicated that CINs were constitutively expressed and share similar expression profiles in all tested samples from S. tuberosum and S. lycopersicum. In addition, in CIN genes of the tomato and potato in response to abiotic and biotic stresses, phytohormones also performed. Overall, CINs in Solanum were encoded by a small and highly conserved gene family, possibly reflecting structural and functional conservation in Solanum. These results lay the foundation for further expounding the functional characterization of CIN genes and are also significant for understanding the evolutionary profiling of the CIN gene family in Solanum.