Genome-scale analyses of polyketide synthases in banana: Phylogenetics and expression profiling forecast their candidacy in specialized metabolism.

Abstract

Plant type III polyketide synthases (PKSs) are associated with various functions in plant growth, development and defense by providing a multitude of polyketide scaffolds for diverse specialized metabolic pathways (SMPs). To decipher banana PKSs involved in specialized metabolism, genome-wide comparative analyses were conducted with A (Musa acuminata) and B (Musa balbisiana) genomes of banana. Both genomes retained eight chalcone synthases (CHSs), seven curcumin synthases (CURSs), three diketidyl-CoA synthases (DCSs) and one anther specific CHS (ASC). Segmental (42%) and tandem (37%) duplication events majorly flourished the banana PKS family. Six of 19 PKSs of A genome (designated as MaPKSs) showed relatively a higher expression in the root, corm, sheath, leaf and embryogenic cell suspension (ECS) of banana. To determine the defense response of MaPKSs and to highlight their candidacy in various SMPs, expression profiling was conducted by qPCR in ECSs treated with 100/200μM of jasmonic acid (JA) and salicylic acid (SA) at 24/48h. Maximum and subordinate expression induction of MaPKSs was apparent respectively against JA and SA treatments. Notably, most MaPKSs achieved their peak expression within 24h of JA and the total flavonoid content was reached maximum within 24h of JA/SA elicitations. Considering the homology, phylogeny, and expression levels in each analyzed sample (n=13), three CHSs, three DCSs along with three CURSs and one ASC were selected as most promising candidates respectively for flavonoids, phenylphenalenones and sporopollenin biosynthesis in banana. Our findings provide a first-line resource to disclose the functions of banana PKSs involved in distinct SMPs.