Investigation of the role of TmMYB16/123 and their targets (TmMTP1/11) in the tolerance of Taxus media to cadmium

The toxicity and stress caused by heavy metal contamination has become an important constraint to the growth and flourishing of trees. In particular, species belonging to the genus Taxus, which are the only natural source for the anti-tumor medicine paclitaxel, are known to be highly sensitive to environmental changes. To investigate the response of Taxus spp. to heavy metal stress, we analyzed the transcriptomic profiles of Taxus media trees exposed to cadmium (Cd2+). In total, six putative genes from the metal tolerance protein (MTP) family were identified in T. media, including two Cd2+ stress inducible TMP genes (TmMTP1, TmMTP11 and Taxus media). Secondary structure analyses predicted that TmMTP1 and TmMTP11, which are members of the Zn-CDF and Mn-CDF subfamily proteins, respectively, contained six and four classic transmembrane domains, respectively. The introduction of TmMTP1/11 into the increment ycf1 yeast cadmium-sensitive mutant strain showed that TmMTP1/11 might regulate the accumulation of Cd2+ to yeast cells. To screen the upstream regulators, partial promoter sequences of the TmMTP1/11 genes were isolated using the chromosome walking method. Several myeloblastosis (MYB) recognition elements were identified in the promoters of these genes. Furthermore, two Cd2+-induced R2R3-MYB TFs, TmMYB16 and TmMYB123, were identified. Both in vitro and in vivo assays confirmed that TmMTB16/123 play a role in Cd2+ tolerance by activating and repressing the expression of TmMTP1/11 genes. The present study elucidated new regulatory mechanisms underlying the response to Cd stress and can contribute to the breeding of Taxus species with high environmental adaptability.

Automated summary

The toxicity and stress caused by heavy metal contamination have a great impact on the growth and survival of trees, especially species belonging to the genus Taxus, which are highly sensitive to changes in the environment. This study analyzed the transcriptomic profiles of Taxus media trees exposed to cadmium (Cd2+) to investigate their response to heavy metal stress. Several metal tolerance protein (MTP) genes, including Cd2+ stress-inducible TMP genes (TmMTP1, TmMTP11), were identified in T. media. Through further analysis, it was found that TmMTP1/11 may regulate the accumulation of Cd2+ in cells. In addition, two Cd2+-induced R2R3-MYB TFs, TmMYB16 and TmMYB123, were identified, and they play a role in Cd2+ tolerance by regulating the expression of TmMTP1/11 genes. Overall, this study provides insights into the regulatory mechanisms of Taxus spp. in response to Cd stress and contributes to the breeding of environmentally adaptable Taxus species.