Diversity, Phylogenetic Relationships, And Expression Profiles Of Invertase Inhibitor Genes In Sweetpotato

Abstract

Invertases and their inhibitor proteins are key regulators of carbon allocation in plants. Manipulation of invertase inhibitor (ITI) activity can potentially increase crop yield. The aim of this study was to determine the sequence diversity, phylogenetic relationships, and expression profiles of ITI genes in sweetpotato(Ipomoea batatas).. The coding sequences of two ITI paralogs (SPITI1 and SPITI2) were cloned from two sweetpotato varieties (Beauregard and Jewel) and sequenced. The DNA sequences were used to deduce amino acids sequences and predicted protein properties. Quantitative PCR (qPCR) was carried out to study the expression profiles of the genes at different developmental stages. The results show that introns are absent in both SPITI paralogs. SNPs, Indels, and variable simple sequence repeats (SSR) were present in the SPITI1 paralog, however, only SNPs were identified in the SPITI2 paralog. The predicted SPITI1 protein had 168, 172, or 174 amino acid residues, and molecular weights ranging from 17.88 to 18.38 kDa. In contrast, SPITI2 coded for a protein with 192 amino acid residues, with molecular weight ranging from 20.59 to 20.65 kDa. All conserved domains of ITI proteins were present in both protein isoforms. Phylogenetic analysis indicated that SPITI genes were more closely related to I.trifida and I.triloba than I.nil, thus, suggesting their evolutionary relationship and conservation. A qPCR study indicated that both SPITI genes were expressed in all the sample tissues, though relative expression values differed across tissues at different developmental stages. This is the first study reporting diversity of SPITI genes and of an ~18 kDA isoform in sweetpotato. The findings may enable design of genetic engineering strategies for SPITI genes, including CRISPR/Cas gene editing in sweetpotato.