A new member of the chalcone synthase (CHS) family in sugarcane

Abstract

Sequences from the sugarcane expressed sequence tag (SUCEST) database were analyzed based on their identities to genes encoding chalcone-synthase-like enzymes. The sorghum (Sorghum bicolor) chalcone-synthase (CHS, EC 2.3.1.74) protein sequence (gi12229613) was used to search the SUCEST database for clusters of sequencing reads that were most similar to chalcone synthase. We found 121 reads with homology to sorghum chalcone synthase, which we were then able to sort into 14 clusters which themselves were divided into two groups (group 1 and group 2) based on the similarity of their deduced amino acid sequences. Clusters in group 1 were more similar to the sorghum enzyme than those in group 2, having the consensus sequence of the active site of chalcone and stilbene synthase. Analysis of gene expression (based on the number of reads from a specific library present in each group) indicated that most of the group 1 reads were from sugarcane flower and root libraries. Group 2 clusters were more similar to the amino acid sequence of an uncharacterized pathogen-induced protein (PI1, gi9855801) from the S. bicolor expressed sequence tag (EST) database. The group 2 clusters sequences and PI1 proteins are 90% identical, having two amino acid changes at the chalcone and stilbene synthase consensi but conserving the cysteine residue at the active site. The PI1 EST has not been previously associated with chalcone synthase and has a different consensus sequence from the previously described chalcone synthase of sorghum. Most of the group 2 reads were from libraries prepared from sugarcane roots and plants infected with Herbaspirillum rubrisubalbicans and Gluconacetobacter diazotroficans. Our results indicate that we have identified a sugarcane chalcone synthase similar to the pathogen-induced PI1 protein found in the sorghum cDNA libraries, and it appears that both proteins represent new members of the chalcone and stilbene synthase super-family.