Fig. 9

Simplified model of the molecular mechanism of MsTMT involved in plant water use efficiency and drought (DR) response. Overexpression of MsTMT in alfalfa represses the transcriptional level of SPCH, which plays a critical role in the initial asymmetric cell division of stomatal development from meristemoid mother cell (MMC) to stomatal-lineage ground cells (SLGCs). This repression causes more MMCs to differentiate into pavement cells resulting in reduced stomatal density that contributes to reduced transpiration rate and further to increased WUE, which probably in turn improves alfalfa drought tolerance. MsTMT also modulates photosynthesis by biochemical processes including light harvesting, non-photochemical quenching (NPQ), Rubisco carboxylation and electron transport capacity. However, the overlapping effect of these factors have limited effect on photosynthetic capacity. MsTMT may response to drought stress involved in ABA-dependent and -independent pathways by regulating MYB, bZIP, WRKY, and RD22 and NAC and DREB1B genes, respectively. The increase in MsTMT gene expression was accompanied by elevated expression of glutathione S-transferase (GST), laccase and gibberellic acid-stimulated Arabidopsis (GASA) genes that play an important role in protection against oxidative stress