Overexpression ofAtALMT1in theArabidopsis thalianaecotype Columbia results in enhanced Al-activated malate excretion and beneficial bacterium recruitment

Abstract

AtALMT1 (Arabidopsis thaliana ALuminum activated Malate Transporter 1) encodes an Arabidopsis thaliana malate transporter that has a pleiotropic role in Arabidopsis stress tolerance. Malate released through AtALMT1 protects the root tip from Al rhizotoxicity, and recruits beneficial rhizobacteria that induce plant immunity. To examine whether the overexpression of AtALMT1 can improve these traits, the gene, driven by the cauliflower mosaic virus 35S promoter, was introduced into the Arabidopsis ecotype Columbia. Overexpression of the gene enhanced both Al-activated malate excretion and the recruitment of beneficial bacteria Bacillus subtilis strain FB17. These findings suggest that overexpression of AtALMT1 can be used as an approach to enhance a plant's ability to release malate into the rhizosphere, which can enhance plant tolerance to some environmental stress factors.

An InDel in the Promoter of Al-ACTIVATED MALATE TRANSPORTER9 Selected during Tomato Domestication Determines Fruit Malate Contents and Aluminum Tolerance

“…Both At-ALMT6 and At-ALMT9 play a role in vacuolar malate transport in guard cells; At-ALMT6 is a Ca 2+ -activated malate channel that does not function in regulating stoma movement and At-ALMT9 is a malate-activated vacuolar chloride channel that does control stomatal aperture and thereby stomatal conductance and drought tolerance. Other members of this family, e.g., Ta-ALMT1, At-ALMT1, Bn-ALMT1, Bn-ALMT2, and Gm-ALMT1, control leaf malate accumulation, malate exudation in root, and affect Al resistance Hurth et al, 2005;Hoekenga et al, 2006;Ligaba et al, 2006;Kobayashi et al, 2013;Liang et al, 2013). In this work, Sl-ALMT9 HMH accessions (e.g., TS40) and Sl-ALMT9 LMH accessions (e.g., TS66) showed significant differences in malate contents in fruits, but contained comparable amounts in leaves.…”

GsMAS1 Encoding a MADS-box Transcription Factor Enhances the Tolerance to Aluminum Stress in Arabidopsis thaliana

“…The qRT-PCR analysis showed that STOP1 was activated by GsMAS1 and Al stress ( Figure 6), which plays essential roles in proton and aluminum toxicities by regulating multiple genes in Arabidopsis [25][26][27]29,30]. The AtALMT1 gene, which is the target gene regulated by STOP1 and the STOP2 gene, which is a homolog of STOP1, were significantly induced by GsMAS1 expression in transgenic Arabidopsis plants with much higher transcription levels ( Figure 6) [19][20][21][22]29]. Previous reports indicated that STOP2 confers Al and low pH tolerance by activating transcription of several genes regulated by STOP1 in Arabidopsis [29].…”

“…The aluminum toxicity caused by aluminum ions that have entered the plant cells can be alleviated mainly through the chelation of organic acids, the aluminum compartment in the vacuole and the combination of protein and other forms of internal detoxification [16][17][18]. Organic acid transporters including aluminum-activated malate transporter1 (ALMT1) and other members of the multidrug and toxic compound extrusion (MATE) citrate transporter family are reported to be involved in the external rejection of the aluminum toxicity mechanism in plants [19][20][21][22]. A recent study suggested that transcription factors also play certain roles in Al stress during the process of plant growth and development, for example, WRKY46 as a transcriptional repressor of ALMT1 regulated aluminum-induced malate secretion in Arabidopsis [23]; WRKY22 improved tolerance to Al stress through activation of FRDL4 and enhancement of citrate secretion in rice [24].…”

The ALMT Gene Family Performs Multiple Functions in Plants

“…This same treatment also induced malate release from the roots. The authors found that the malate release helped recruit the beneficial bacterium Bacillus FB17 around the roots [16,31]. Furthermore, AtALMT1 expression was induced by flg22, a kind of MAMP (microbe-associated molecular pattern) in a manner that was independent of the salicylic acid and jasmonic acid pathways [55].…”

“…Malate chelates the Al 3+ which reduces damage to the cell wall, membranes and other cellular components. Other members of the family perform similar functions in Arabidopsis [3,31], rape (Brassica napus L.) [4], rye (Secale cereale L.) [2], soybean (Glycine max L.) [32], alfalfa (Medicago sativa L.) [33], and Yorkshire fog (Holcus lanatus L.) [34]. Regulation of these vary and some show more complex interactions [35].…”