The team of Shanghai Jiaotong University Anyuan revealed the molecular mechanism of transcription factor MsMYB741 to regulate alfalfa's resistance to aluminum toxicity

Medicago sativa, a perennial herb of the legume family, is the most widely cultivated leguminous pasture in the world, with high protein content, rich vitamin and mineral content, high grass production, and has the reputation
of "king of pastures".
In the southern red soil area of China, due to the strong acid, highly active aluminum (Al3+) characteristics of red soil, it has a great inhibitory effect on the growth and development of alfalfa, which seriously restricts the development of
animal husbandry in southern grassland.
Therefore, it is urgent to carry out research on the mechanism of alfalfa resistance to aluminum toxicity to provide genetic resources and theoretical support
for further molecular breeding of alfalfa resistant to aluminum toxicity.

Recently, the team of Professor An Yuan of the College of Agriculture and Biology of Shanghai Jiaotong University published a research paper entitled MsMYB741 is involved in alfalfa resistance to aluminum stress by regulating flavonoid biosynthesis online in The Plant Journal.
The mechanism
of positive regulation of alfalfa flavonoids and improvement of alfalfa resistance of alfalfa was revealed by the MYB transcription factor MsMYB741.

MYB transcription factor is one of the largest families of transcription factors in plants, and is widely involved in many molecular and physiological processes
including abiotic stress response responses and secondary metabolic regulation.
Flavonoids are a large class of very important, polyphenol-containing plant secondary metabolites, with antioxidant, chelating metal ions and other functions
.
The research group found a number of differential expression genes from the gene chip of aluminium stress alfalfa seedlings, and after analysis and screening, the MYB gene MsMYB741, which was significantly upregulated by aluminum stress treatment and highly correlated with flavonoid gene expression, was selected as a candidate gene
.
Preliminary studies have found that overexpression of this gene in the hairy roots of alfalfa can significantly improve the resistance of transgenic strains to
aluminum poisoning.
Subsequently, with wild-type (WT) alfalfa as the receptor, MsMYB741 overexpression (OE) and interference expression (RNAi) plants were obtained, and the aluminum stress treatment experiments showed that the overexpression of MsMYB741 significantly reduced the Al content in the plant and improved the resistance of the transgenic line, while the RNAi plant showed the opposite phenotype (Figure 1), at the same time, the total antioxidant capacity of the overexpressed strain was significantly increased, and the content of O2- and MDA in alfalfa under aluminum stress was significantly reduced.
The main reason is that the total flavonoids content of overexpressed strains has increased significantly, and the reactive oxygen species induced by Al stress are effectively removed
.

Fig.
1 Overexpression MsMYB741 improves alfalfa's resistance to aluminum poisoning

Further studies showed that MsMYB741 was regulating the expression of MsPAL and MsCHI, promoting total flavonoid accumulation, increasing alfalfa root flavonoid secretion, and reducing the Al content
in the overexpressed strain.
In addition, the study also found that the MsABF2 protein in response to ABA signal is the upstream regulator of MsMYB741, positively regulating its expression by binding to the ABRE element in the MsMYB741 promoter, based on which the authors constructed a working model of ABA-MsABF2-MsMYB741-MsPAL/MsCHI to improve alfalfa's ability to resist aluminum toxicity (Figure 2).

Figure 2 MsABF2 is regulating MsMYB741 expression

In summary, MsMYB741 has important biological functions in improving alfalfa resistance to aluminum toxicity, promoting the synthesis and accumulation of alfalfa flavonoids by positively regulating the expression of MsPAL and MsCHI, removing reactive oxygen species (ROS) caused by aluminum stress on the one hand, and reducing oxidative damage of the plasma membrane system; On the other hand, it increases the secretion of root flavonoids to chel Al3+, reduces the Al content in plants, and improves the aluminum stress resistance of overexpressed alfalfa strains
.

Su Liantai (now a postdoctoral fellow in the research group) is the first author of the paper, Professor An Yuan is the corresponding author, postdoctoral students Lv Aimin and Wen Wuwu, doctoral students Fan Nana and Gao Li, and graduate doctoral students Li Jiaojiao and Associate Professor Zhou Peng participated in the study
.
The research has been supported by projects such as the National Natural Science Foundation of China (Surface and Youth Program) and the China Postdoctoral Science Foundation
.

Paper Link: https://onlinelibrary.
wiley.
com/doi/10.
1111/tpj.
15977