Yanyan Ma, Maofu Xue, Xiaofei Zhang, Songbi Chen

BMC Plant Biology; 2023 Apr 28;23(1): 227. doi: 10.1186/s12870-023-04174-2.

Background: Cassava (Manihot esculenta Crantz) is widely planted in tropical and several subtropical regions in which drought, high temperatures, and other abiotic stresses occur. Metallothionein (MT) is a group of conjugated proteins with small molecular weight and rich in cysteine. These proteins play a substantial role in response to physiological stress through the regulation of reactive oxygen species (ROS). However, the biological functions of MT genes in cassava are unknown.

Results: A total of 10 MeMT genes were identified in the cassava genome. The MeMTs were divided into 3 groups (Types 2-4) based on the contents and distribution of Cys residues. The MeMTs exhibited tissue-specific expression and located on 7 chromosomes. The MeMT promoters contain some hormones regulatory and stresses responsiveness elements. MeMTs were upregulated under hydrogen peroxide (H₂O₂) treatment and in respond to post-harvest physiological deterioration (PPD). The results were consistent with defense-responsive cis-acting elements in the MeMT promoters. Further, four of MeMTs were selected and silenced by using the virus-induced gene silencing (VIGS) method to evaluate their functional characterization. The results of gene-silenced cassava suggest that MeMTs are involved in oxidative stress resistance, as ROS scavengers.

Conclusion: We identified the 10 MeMT genes, and explore their evolutionary relationship, conserved motif, and tissue-specific expression. The expression profiles of MeMTs under three kinds of abiotic stresses (wounding, low-temperature, and H₂O₂) and during PPD were analyzed. The tissue-specific expression and the response to abiotic stresses revealed the role of MT in plant growth and development. Furthermore, silenced expression of MeMTs in cassava leaves decreased its tolerance to ROS, consistent with its predicted role as ROS scavengers. In summary, our results suggest an important role of MeMTs in response to physiological stress as well as species adaptation via the regulation of ROS homeostasis.

See https://pubmed.ncbi.nlm.nih.gov/37118665/

Fig. 3 Gene structure, conserved protein motifs and chromosomal distribution of MeMTs. (A) The phylogenetic tree comprising 10 MeMT genes was generated via the MEGA 7.0 program, which included the exon‒intron structures of the 10 MeMT genes. Five patterns of conserved protein motifs were depicted in different colored boxes. (B) Chromosome distribution of MeMT genes. 10 MeMT genes were mapped onto the 7 Chromosomes of cassava.