Genome-Wide Identification and Characterization of the HMGR Gene Family in Taraxacum kok-saghyz Provide Insights into Its Regulation in Response to Ethylene and Methyl Jsamonate Treatments

<i>HMGR</i> (3-hydroxy-3-methylglutaryl-CoA reductase) plays a crucial role as the first rate-limiting enzyme in the mevalonate (MVA) pathway, which is the upstream pathway of natural rubber biosynthesis. In this study, we carried out whole-genome identification of <i>Taraxacum kok-saghyz</i> (TKS), a novel rubber-producing alternative plant, and obtained six members of the <i>TkHMGR</i> genes. Bioinformatic analyses were performed including gene structure, protein properties, chromosomal localization, evolutionary relationships, and cis-acting element analyses. The results showed that <i>HMGR</i> genes were highly conserved during evolution with a complete HMG-CoA reductase conserved domain and were closely related to <i>Asteraceae</i> plants during the evolutionary process. The α-helix is the most prominent feature of the secondary structure of the TkHMGR proteins. Collinearity analyses demonstrated that a whole-genome duplication (WGD) event and tandem duplication event play a key role in the expansion of this family and <i>TkHMGR1</i> and <i>TkHMGR6</i> have more homologous gene between other species. Cis-acting element analysis revealed that the <i>TkHMGR</i> gene family had a higher number of MYB-related, light-responsive, hormone-responsive elements. In addition, we investigated the expression patterns of family members induced by ethylene (ETH) and methyl jasmonate (MeJA), and their expression levels at different stages of <i>T. kok-saghyz</i> root development. Finally, subcellular localization results showed that six TkHMGR members were all located in the endoplasmic reticulum. In conclusion, the results of our study lay a certain theoretical basis for the subsequent improvement of rubber yield, molecular breeding of rubber-producing plants, and genetic improvement of <i>T. kok-saghyz</i>.