Functional characterization of three MATE genes in relation to aluminum-induced citrate efflux from soybean root

Abstract

Citrate transporters responsible for Aluminum (Al)-induced citrate efflux have not been identified in soybean. Three soybean multi-drug and toxic compound extrusion (MATE) family genes were characterized by transcriptional expression, subcellular localization and overexpression experiments. GmMATE75, GmMATE79 and GmMATE87 are localized to plasma membrane. Their over-expression respectively resulted in more citrate efflux and less Al contents in soybean hairy roots, alleviated root elongation inhibition in Arabidopsis and partially restored root growth in atmate mutant under Al stress. Al increased their transcriptional expression at either the root apex or the base zone. Cu2+, Cd2+, La3+ increased the expression of GmMATE79 and GmMATE87. Ten day of –Fe culture increased the expression of GmMATE75 and GmMATE79. Al treatment extended β-glucuronidase (GUS) staining from central cylinder to cortical and epidermis cells for pGmMATE75::GUS or pGmMATE79::GUS soybean hairy roots transformation. But GUS staining restricted within central cylinder for pGmMATE87::GUS transformation with or without Al treatment. GmMATE75, GmMATE79 and GmMATE87 are plasma-membrane-localized citrate transporters and have capabilities to increase citrate efflux. They played different role in Al-induced citrate secretion from soybean because their different tissue localization and expression patterns.