Malate synthesis and secretion mediated by a manganese-enhanced malate dehydrogenase confers superior manganese tolerance in Stylosanthes guianensis.
Manganese (Mn) toxicity is a major constraint limiting plant growth on acidic soils. Superior Mn tolerance in Stylosanthes spp. has been well documented, but its molecular mechanisms remain largely unknown. In this study, superior Mn tolerance in Stylosanthes guianensis was confirmed, as reflected by a high Mn toxicity threshold. Furthermore, genetic variation of Mn tolerance was evaluated using two S. guianensis genotypes, which revealed that the Fine-stem genotype had higher Mn tolerance than the TPRC2001-1 genotype, as exhibited through less reduction in dry weight under excess Mn, and accompanied by lower internal Mn concentrations. Interestingly, Mn-stimulated increases in malate concentrations and exudation rates were observed only in the Fine-stem genotype. Proteomic analysis of Fine-stem roots revealed that S. guianensis Malate Dehydrogenase1 (SgMDH1) accumulated in response to Mn toxicity. Western-blot and quantitative PCR analyses showed that Mn toxicity resulted in increased SgMDH1 accumulation only in Fine-stem roots, but not in TPRC2001-1. The function of SgMDH1-mediated malate synthesis was verified through in vitro biochemical analysis of SgMDH1 activities against oxaloacetate, as well as in vivo increased malate concentrations in yeast (Saccharomyces cerevisiae), soybean (Glycine max) hairy roots, and Arabidopsis (Arabidopsis thaliana) with SgMDH1 overexpression. Furthermore, SgMDH1 overexpression conferred Mn tolerance in Arabidopsis, which was accompanied by increased malate exudation and reduced plant Mn concentrations, suggesting that secreted malate could alleviate Mn toxicity in plants. Taken together, we conclude that the superior Mn tolerance of S. guianensis is achieved by coordination of internal and external Mn detoxification through malate synthesis and exudation, which is regulated by SgMDH1 at both transcription and protein levels.
State Key Laboratory for Conservation and Utilization of Subtropical Agro-Bioresources, Root Biology Center, South China Agricultural University, Guangzhou 510642, China (Z.C., L.S., P.L., J.T., H.L.); andInstitute of Tropical Crop Genetic Resources, Chinese Academy of Tropical Agriculture Sciences, College of Agriculture, Hainan University, Haikou 571101, China (L.S., P.L., G.L.).
Zhijian
Z
Chen
State Key Laboratory for Conservation and Utilization of Subtropical Agro-Bioresources, Root Biology Center, South China Agricultural University, Guangzhou 510642, China (Z.C., L.S., P.L., J.T., H.L.); andInstitute of Tropical Crop Genetic Resources, Chinese Academy of Tropical Agriculture Sciences, College of Agriculture, Hainan University, Haikou 571101, China (L.S., P.L., G.L.).
Lili
L
Sun
State Key Laboratory for Conservation and Utilization of Subtropical Agro-Bioresources, Root Biology Center, South China Agricultural University, Guangzhou 510642, China (Z.C., L.S., P.L., J.T., H.L.); andInstitute of Tropical Crop Genetic Resources, Chinese Academy of Tropical Agriculture Sciences, College of Agriculture, Hainan University, Haikou 571101, China (L.S., P.L., G.L.).
Pandao
P
Liu
State Key Laboratory for Conservation and Utilization of Subtropical Agro-Bioresources, Root Biology Center, South China Agricultural University, Guangzhou 510642, China (Z.C., L.S., P.L., J.T., H.L.); andInstitute of Tropical Crop Genetic Resources, Chinese Academy of Tropical Agriculture Sciences, College of Agriculture, Hainan University, Haikou 571101, China (L.S., P.L., G.L.).
Guodao
G
Liu
State Key Laboratory for Conservation and Utilization of Subtropical Agro-Bioresources, Root Biology Center, South China Agricultural University, Guangzhou 510642, China (Z.C., L.S., P.L., J.T., H.L.); andInstitute of Tropical Crop Genetic Resources, Chinese Academy of Tropical Agriculture Sciences, College of Agriculture, Hainan University, Haikou 571101, China (L.S., P.L., G.L.) jtian@scau.edu.cn.
Jiang
J
Tian
State Key Laboratory for Conservation and Utilization of Subtropical Agro-Bioresources, Root Biology Center, South China Agricultural University, Guangzhou 510642, China (Z.C., L.S., P.L., J.T., H.L.); andInstitute of Tropical Crop Genetic Resources, Chinese Academy of Tropical Agriculture Sciences, College of Agriculture, Hainan University, Haikou 571101, China (L.S., P.L., G.L.).
Hong
H
Liao
D000222:Adaptation, Physiological / Q000502:physiology; D007887:Fabaceae / Q000201:enzymology / Q000378:metabolism / Q000502:physiology*; D008291:Malate Dehydrogenase / Q000187:drug effects / Q000502:physiology*; D008293:Malates / Q000378:metabolism*; D008345:Manganese / Q000633:toxicity*; D010935:Plant Diseases / Q000139:chemically induced; D018517:Plant Roots / Q000378:metabolism / Q000502:physiology; D040901:Proteomics
D008293:Malates; D008345:Manganese; C030298:malic acid; D008291:Malate Dehydrogenase