Comparative Molecular Evolution of Chitinases in Response to Mycoparasitic Interactions

• Main Authors: Katarina Ihrmark, Nashwan Asmail, Wimal Ubhayasekera, Petter Melin, Jan Stenlid, Magnus Karlsson
• Format: Article
• Language: English
• Published: SAGE Publishing 2010-01-01
• Series: Evolutionary Bioinformatics
• Online Access: https://doi.org/10.4137/EBO.S4198

Certain species of the fungal genus Trichoderma are potent mycoparasites and are used for biological control of fungal diseases on agricultural crops. In Trichoderma , whole-genome sequencing reveal between 20 and 36 different genes encoding chitinases, hydrolytic enzymes that are involved in the mycoparasitic attack. Sequences of Trichoderma chitinase genes chi18-5, chi18-13, chi18-15 and chi18-17 , which all exhibit specific expression during mycoparasitism-related conditions, were determined from up to 13 different taxa and studied with regard to their evolutionary patterns. Two of them, chi18-13 and chi18-17 , are members of the B1/B2 chitinase subgroup that have expanded significantly in paralog number in mycoparasitic Hypocrea atroviridis and H. virens. Chi18-13 contains two codons that evolve under positive selection and seven groups of co-evolving sites. Chi18-15 displays a unique codon-usage and contains five codons that evolve under positive selection and three groups of co-evolving sites. Regions of high amino acid variability are preferentially localized to substrate- or product side of the catalytic clefts. Differences in amino acid diversity/conservation patterns between different Trichoderma clades are observed. These observations show that Trichoderma chitinases chi18-13 and chi18-15 evolve in a manner consistent with rapid co-evolutionary interactions and identifies putative target regions involved in determining substrate-specificity.