Aluminum-activated citrate and malate transporters from the MATE and ALMT families function independently to confer Arabidopsis aluminum tolerance.
Aluminum-activated root malate and citrate exudation play an important role in plant Al tolerance. This paper characterizes AtMATE, a homolog of the recently discovered sorghum and barley Al-tolerance genes, shown here to encode an Al-activated citrate transporter in Arabidopsis. Together with the previously characterized Al-activated malate transporter, AtALMT1, this discovery allowed us to examine the relationship in the same species between members of the two gene families for which Al-tolerance genes have been identified. AtMATE is expressed primarily in roots and is induced by Al. An AtMATE T-DNA knockdown line exhibited very low AtMATE expression and Al-activated root citrate exudation was abolished. The AtALMT1 AtMATE double mutant lacked both Al-activated root malate and citrate exudation and showed greater Al sensitivity than the AtALMT1 mutant. Therefore, although AtALMT1 is a major contributor to Arabidopsis Al tolerance, AtMATE also makes a significant but smaller contribution. The expression patterns of AtALMT1 and AtMATE and the profiles of Al-activated root citrate and malate exudation are not affected by the presence or absence of the other gene. These results suggest that AtALMT1-mediated malate exudation and AtMATE-mediated citrate exudation evolved independently to confer Al tolerance in Arabidopsis. However, a link between regulation of expression of the two transporters in response to Al was identified through work on STOP1, a transcription factor that was previously shown to be necessary for AtALMT1 expression. Here we show that STOP1 is also required for AtMATE expression and Al-activated citrate exudation.
Liu
Jiping
J
US Plant Soil and Nutrition Laboratory, USDA-ARS, Cornell University, Ithaca, NY 14853, USA.
Magalhaes
Jurandir V
JV
Shaff
Jon
J
Kochian
Leon V
LV
D000535:Aluminum / Q000378:metabolism*; D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000235:genetics* / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D019343:Citric Acid / Q000378:metabolism; D018506:Gene Expression Regulation, Plant; D008293:Malates / Q000378:metabolism; D008969:Molecular Sequence Data; D027361:Organic Anion Transporters / Q000235:genetics / Q000378:metabolism*; D010802:Phylogeny; D018517:Plant Roots / Q000235:genetics / Q000378:metabolism; D018749:RNA, Plant / Q000235:genetics; D016415:Sequence Alignment; D014157:Transcription Factors / Q000378:metabolism
C512361:ALMT1 protein, Arabidopsis; D029681:Arabidopsis Proteins; D002352:Carrier Proteins; D008293:Malates; D027361:Organic Anion Transporters; D018749:RNA, Plant; C525886:STOP1 protein, Arabidopsis; D014157:Transcription Factors; C020723:citrate-binding transport protein; D019343:Citric Acid; C030298:malic acid; D000535:Aluminum