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