Submitted to: Plant Cell and Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 3, 2011
Publication Date: December 12, 2011
Citation: Yang, X., Yang, J., Pineros, M., Kochian, L.V., Zheng, S. 2011. Title A de novo synthesis citrate transporter VuMATE confers aluminum resistance in rice bean (vigna umbellata). Plant Cell and Environment. 34:2138-2148. Interpretive Summary: Large areas of land within the U.S. and over 40% of the world’s arable lands are acidic. In these acid soils, aluminum (Al) toxicity is the primary factor limiting crop production via Al-induced inhibition of root growth. The physiological and molecular basis for Al tolerance is still poorly understood. Thus, we need a more complete understanding of the mechanisms underlying Al tolerance if we are going to be able to develop more Al tolerant crop plants for improved cultivation on acid soils. In this paper, we used molecular and physiological methods to study Al tolerance in the highly Al tolerant legume species, Vigna umbellate (ricebean), that we previously had shown uses Al-activated citrate efflux from the roots to mediate a high level of Al tolerance. In this study we showed that a homolog of the major Al tolerance gene we previously identified in sorghum that is a member of the MATE family of organic efflux transporters is the primary Al tolerance gene in rice bean. We show here that it is expressed primarily in the root tip, requires an extended period of exposure to Al to increase expression and abundance of this transport protein. This research also shows that although similar genes confer Al tolerance in both cereal and bean species via similar mechanisms, they are regulated in different ways. This research is providing a deeper understanding of the strategies plants use to tolerate toxic Al on acid soils and will help us in developing more Al tolerant crops for agriculture on acid soils that are widespread both in the US and also in developing countries.
Technical Abstract: Al-activated organic acid anion efflux from roots is an important Al resistance mechanism in plants. We have conducted the homologous cloning and isolation of VuMATE (Vigna umbellata multidrug and toxic compound extrusion), a gene encoding a de novo citrate transporter from rice bean. Al treatment upregulated VuMATE expression in the root apex, but did not increase its expression in mature root regions or in the leaf. The degree of upregulation of VuMATE was both Al concentration and time dependent, consistent with the delay in the onset of the Al-induced citrate efflux in rice bean roots. While La3+ moderately induced VuMATE expression, Cd2+ and Cu2+ did not induce expression. Electrophysiological analysis of Xenopus oocytes expressing VuMATE indicated this transporter can mediate significant anion efflux across the plasma membrane. [14C]citrate efflux experiments in Xenopus oocytes demonstrated VuMATE is a H+-dependent citrate efflux transporter. In addition, expression of VuMATE in transgenic tomato plants resulted in increased Al resistance which correlated with an enhanced root citrate efflux. Taken together, these findings suggest that VuMATE is a functional homolog of the known citrate transporters in sorghum, barley, maize and Arabidopsis. The similarities and differences of all the known citrate transporters associated with Al stress in MATE family are also discussed.