An exclusion mechanism is epistatic to an internal detoxification mechanism in aluminum resistance in Arabidopsis

BACKGROUND: In Arabidopsis, the aluminum (Al) exclusion mechanism is mainly facilitated by ALMT1-mediated malate exudation and MATE-mediated citrate releases from the root. Recently, we have demonstrated that coordinated functioning between an ALMT1-mediated Al exclusion mechanism, via exudation of malate from the root tip, and a NIP1;2-facilitated internal detoxification mechanism, via removal of Al from the root cell wall and subsequent root-to-shoot Al translocation, plays critical roles in achieving overall Al resistance. However, the genetic relationship between ALMT1 and NIP1;2 in these processes remained unclear. RESULTS: Through genetic and physiological analyses, we demonstrate that unlike ALMT1 and MATE, which function independently and additively, ALMT1 and NIP1;2 show an epistatic relationship in Al resistance. These results indicate that ALMT1 and NIP1;2 function in the same biochemical pathway, whereas ALMT1 and MATE in different ones. CONCLUSION: The establishment of the epistatic relationship and the coordinated functioning between the ALMT1 and NIP1;2-mediated exclusion and internal detoxification mechanisms are pivotal for achieving overall Al resistance in the non-accumulating Arabidopsis plant. We discuss and emphasize the indispensable roles of the root cell wall for the implementation of the Al exclusion mechanism and for the establishment of an epistatic relationship between the ALMT1-mediated exclusion mechanism and the NIP1;2-facilitated internal detoxification mechanism.