4.1 Evolution of the structural and regulatory genes in the GSH
metabolic pathway
In this study, we reexamined the evolutionary patterns of the coding
genes of 12 key enzymes in the GSH pathway at the genome-wide level of
upland cotton. As a result, we not only found duplicated characteristics
of 12 structural enzyme gene families, but also revealed the complex
expression patterns of the gene members in each family. Using the
largest GST family as an example, we identified 121 GST members from the cotton genome (UTX_v2.1). Further analyses revealed
that these genes were associated with 76 loci, 59% of which showed
amplification due to additivity of biparental subgenomic homoeologs. In
addition, in our ML tree (Fig. 2), the topological
clustering of these GST genes corresponds exactly to their nine classes
of functional annotations (DHAR, EF1Bγ, Lambda, MGST, Phi, Tau, TCHQD,
Theta, and Zeta). This phylogenetic profile indicates that functional
redifferentiation may be a significant factor contributing to the
expansion of this gene family. Notably, in this study, we newly
identified four MGST genes (two loci). However, in our ML
tree, these genes are not included in the clade where most of the other
GST genes are placed. In eukaryotes, GSTs can be subdivided into three
major protein families based on their cellular localization: cytosolic
GSTs, mitochondrial GSTs, and microsomal GSTs. Microsomal GSTs (MGST),
also known as MAPEG (membrane-associated proteins involved in eicosanoid
and glutathione metabolism), are integral membrane proteins that are not
evolutionarily related to the other major classes