The varied functions of aluminium-activated malate transporters–much more than aluminium resistance

Abstract

The ALMT (aluminium-activated malate transporter) family comprises a functionally diverse but structurally similar group of ion channels. They are found ubiquitously in plant species, expressed throughout different tissues, and located in either the plasma membrane or tonoplast. The first family member identified was TaALMT1, discovered in wheat root tips, which was found to be involved in aluminium resistance by means of malate exudation into the soil. However, since this discovery other family members have been shown to have many other functions such as roles in stomatal opening, general anionic homoeostasis, and in economically valuable traits such as fruit flavour. Recent evidence has also shown that ALMT proteins can act as key molecular actors in GABA (γ-aminobutyric acid) signalling, the first evidence that GABA can act as a signal transducer in plants.

Genome-Wide Identification of Aluminum-Activated Malate Transporter (ALMT) Gene Family in Rubber Trees (Hevea brasiliensis) Highlights Their Involvement in Aluminum Detoxification

“…Subsequently, ALMT genes were identified from many plants and proved to be related to many physiological processes in plant, such as Al detoxification, mineral nutrition, stomatal movement, fruit acidity, seed development, and other abiotic stress [24,[38][39][40]. It was found that there were 14 ALMT members in Arabidopsis thaliana, 16 members in Fragaria vesca, 9 members in rice, 27 members in Pyrus bretschneideri, 25 members in Malus domestica, 25 members in Prunus mume [22,23,38,41]. However, little is known to the ALMT genes in rubber trees.…”

“…Genes encoding malate transporters have been found in many plant species, such as Arabidopsis (AtALMT1), rape (BnALMT1, BnALMT2), rye (ScALMT1), and soybean (GmALMT1) [18][19][20][21]. Furthermore, more studies showed that members of the ALMT family were not only associated with Al resistance but also participated in other physiological processes, including stomatal movement, cellular signaling, cell expansion, nutrients acquisition, fruit flavor regulation, and GABA (γ-aminobutyric acid) signaling [22][23][24]. Nevertheless, the ALMT family member has not been reported in the rubber trees.…”

Split personality of Aluminum Activated Malate Transporter family proteins: facilitation of both GABA and malate transport

“…Anion transport via ALMTs is an important and well accepted mechanism for signalling (Bouche et al, 2003a; Roberts, 2007; Pineros et al, 2008; Dreyer et al, 2013; Ligaba et al, 2013; Ramesh et al, 2015), stomatal pore regulation (Meyer et al, 2010; Roelfsema et al, 2012; De Angeli et al, 2013; Kollist et al, 2014; Palmer et al, 2016), phosphorous nutrition (Liang et al, 2013; Balzergue et al, 2017) and for providing tolerance to Al 3+ at low pH (Delhaize and Ryan, 1995; Sasaki T, 2004; Zhang et al, 2008; Ryan et al, 2011). We have demonstrated that TaALMT1 is able to facilitate GABA efflux and influx at very high rates.…”

The role of transposable elements in the evolution of aluminium resistance in plants

“…More than 30 additional genes encoding OA transporters have been linked with Al resistance in other species including most important crops (Table 1). These OA transporters are encoded by two gene families: the Al-activated malate transporter (ALMT) family encodes anion channels that release malate from cells, and the multidrug and toxic compound extrusion (MATE) family encodes co-transporters that release citrate from cells (Takanashi et al, 2014;Palmer et al, 2016;Sharma et al, 2016). Some of the genes in Table 1 have a strong genetic and physiological association with Al resistance, but for others, the links remain correlative and further confirmation is required.…”