Molecular Evolution and Expression Divergence of HMT Gene Family in Plants

Abstract

Homocysteine methyltransferase (HMT) converts homocysteine to methionine using <i>S</i>-methylmethionine (SMM) or <i>S</i>-adenosylmethionine (SAM) as methyl donors in organisms, playing an important role in supplying methionine for the growth and the development of plants. To better understand the functions of the <i>HMT</i> genes in plants, we conducted a wide evolution and expression analysis of these genes. Reconstruction of the phylogenetic relationship showed that the <i>HMT</i> gene family was divided into Class 1 and Class 2. In Class 1, <i>HMT</i>s were only found in seed plants, while Class 2 presented in all land plants, which hinted that the <i>HMT</i> genes might have diverged in seed plants. The analysis of gene structures and selection pressures showed that they were relatively conserved during evolution. However, type I functional divergence had been detected in the <i>HMT</i>s. Furthermore, the expression profiles of <i>HMT</i>s showed their distinct expression patterns in different tissues, in which some <i>HMT</i>s were widely expressed in various organs, whereas the others were highly expressed in some specific organs, such as seeds or leaves. Therefore, according to our results in the evolution, functional divergence, and expression, the <i>HMT</i> genes might have diverged during evolution. Further analysis in the expression patterns of <i>AthHMT</i>s with their methyl donors suggested that the diverged <i>HMT</i>s might be related to supply methionine for the development of plant seeds.