Altered Profile of Secondary Metabolites in the Root Exudates of Arabidopsis ATP-Binding Cassette Transporter Mutants

Abstract

Following recent indirect evidence suggesting a role for ATP-binding cassette (ABC) transporters in root exudation of phytochemicals, we identified 25 ABC transporter genes highly expressed in the root cells most likely to be involved in secretion processes. Of these 25 genes, we also selected six full-length ABC transporters and a half-size transporter for in-depth molecular and biochemical analyses. We compared the exuded root phytochemical profiles of these seven ABC transporter mutants to those of the wild type. There were three nonpolar phytochemicals missing in various ABC transporter mutants compared to the wild type when the samples were analyzed by high-performance liquid chromatography-mass spectrometry. These data suggest that more than one ABC transporter can be involved in the secretion of a given phytochemical and that a transporter can be involved in the secretion of more than one secondary metabolite. The primary and secondary metabolites present in the root exudates of the mutants were also analyzed by gas chromatography-mass spectrometry, which allowed for the identification of groups of compounds differentially found in some of the mutants compared to the wild type. For instance, the mutant Atpdr6 secreted a lower level of organic acids and Atmrp2 secreted a higher level of amino acids as compared to the wild type. We conclude that the release of phytochemicals by roots is partially controlled by ABC transporters.

Kin recognition is a nutrient-dependent inducible phenomenon

“…[11][12][13][14][15] Sodium orthovanadate (Na 3 VO 4 ), a generic ABC-transport inhibitor, which blocks the release and/or uptake of root exudates, eliminated the increased lateral root number observed during KR studies with different accessions of A. thaliana. 19,20 These findings underscore the importance of such low-molecular weight secondary metabolites in mediating KR (Fig. 1).…”

Spatio Temporal Influence of Isoflavonoids on Bacterial Diversity in the Soybean Rhizosphere

“…In the latter case, the availability of genetic mutants impaired in biosynthesis and transport of specific rhizodeposit compounds has been crucial. For example, mutations in an Arabidopsis thaliana ABC-transporter gene, ABCG30 (resulting in increased exudation of phenolic acids and reduced exudation of sugars), caused significant changes in root microbial community structure as assayed by high-throughput sequencing of rRNA gene amplicons (Badri et al 2008(Badri et al , 2009). This study revealed the association of a number of potentially beneficial bacteria with abcg30 mutant roots.…”

Microbe-Associated Molecular Patterns-Triggered Root Responses Mediate Beneficial Rhizobacterial Recruitment in Arabidopsis

“…Some of the recent reports indicate that the hormonal activation of ISR by ET/JA or SAR by SA showed no significant effect on the density and structure of the rhizosphere bacterial community (Doornbos et al, 2011). On the contrary, a recent report suggests that ATP-binding cassette transporters involved in root secretions may structure the rhizospheric microbiome (Badri et al, 2008). Carbon enrichment of the rhizosphere especially carboxylate excretion and acidification at the root surface might have a strong general impact on structuring rhizospheric microbial communities (Marschner et al, 2002).…”