Genome-wide Analysis of ZRT/IRT Like Protein (ZIP) Family Genes in Carica papaya and Expression Profile Analysis during Fruiting Stage

Abstract

The papaya (Carica papaya) fruit is considered to be a miracle fruit contains zinc (Zn) and iron (Fe) in abundant amount. The zinc and iron regulated transporter like protein (ZIP) in plants are known to be critically involved in uptake, transport and cellular homeostasis of Zn and Fe. However, comprehensive characterization and role of ZIP family in papaya plant is still missing. In the present study, nine members of ZIP transporter were identified in the papaya genome. The genes were named accordingly as CpZIP1 to CpZIP9. Sequence analysis shows that they putatively encode proteins of 343 to 486 amino acid length with six to nine transmembrane (TM) domains. Phylogenetically, the ZIP genes were clustered into four subfamilies similar to the ZIP family in Arabidopsis thaliana. Gene ontology (GO) analysis shows the processes of transmembrane transport, divalent inorganic cation transport, metal ion transport, inorganic molecular entity transmembrane transporter activity are highly enriched among all the Papaya ZIP genes. Gene expression analysis indicates five out of nine ZIP members are sharply up-regulated during the fruiting stage whereas three genes (CpZIP2, CpZIP5 and CpZIP7) exhibited moderate level of expression. Homology modeling revealed amino acid-like isoleucine, histidine, leucine, glycine, valine are highly conserved among ZIP genes. Mutational sensitivity assay indicates the ZIP proteins in papaya are not sensitive to mutation and are highly stable.  The result of our study contributes to the first comprehensive information about phylogenetic relationship, putative functional divergence of ZIP family genes in papaya.