Abstract
The roots of plants secrete compounds as a way to exchange information with organisms living in the soil. Here, we report the involvement of seven root-expressed ATP-binding cassette (ABC) transporters corresponding to both full and half-size molecules (Atabcg36, Atabcg37, Atabcc5, Atabcf1, Atabcf3, Atnap5, and Atath10) in root exudation processes using Arabidopsis thaliana. Root exuded phytochemicals were analyzed by high-performance liquid chromatography-mass spectrometry (HPLC-MS) and gas chromatography-mass spectrometry (GC-MS), and it was determined that some of the root exudates from the corresponding ABC transporter mutants were significantly different compared to the wild type. For example, Atabcg37 and Atabcc5 secreted higher levels of the phytoalexin camalexin, and Atabcg36 secreted higher levels of organic acids, specifically salicylic acid (SA). Furthermore, we analyzed the root tissue metabolites of these seven ABC transporter mutants and found that the levels of SA, quercetin, and kaempferol glucosides were higher in Atabcg36, which was correlated with higher expression levels of defense genes in the root tissues compared with the wild type. We did not observe significant changes in the root exudates of the half-size transporters except for Atabcf1 that showed lower levels of few organic acids. In summary, full-size transporters are involved in root secretion of phytochemicals.
Highlights
ATP-binding cassette (ABC) transporters are one of the largest protein families in bacteria, fungi, plants, and animals, including both membrane bound and soluble proteins (Henikoff et al, 1997; Yazaki, 2005; Rea, 2007; Verrier et al, 2008; Yazaki et al, 2009)
The ABC proteins encompass a large protein family ubiquitous in all organisms, which includes both membrane bound and soluble proteins (Higgins, 1992; Yazaki et al, 2009). These proteins are classified as primary transporters which are directly energized by ATP hydrolysis to translocate solutes across cellular membranes (Higgins, 1992), a process that is independent of membrane potential and proton gradients across the membrane
Www.frontiersin.org root exudate profiles revealed that one compound (Rt = 13.8 and M + = 277) was completely absent in Atabcg37 compared with the wild type and the other mutants used in this study
Summary
ATP-binding cassette (ABC) transporters are one of the largest protein families in bacteria, fungi, plants, and animals, including both membrane bound and soluble proteins (Henikoff et al, 1997; Yazaki, 2005; Rea, 2007; Verrier et al, 2008; Yazaki et al, 2009). ABC transporters are responsible for the transportation of a multitude of compounds (Kang et al, 2010). They are involved in the excretion (extracellular over the plasma membrane or intracellular into the vacuoles of plants) of potentially toxic compounds, lipid translocation, transport of steroids and their derivatives, conferring heavy metal tolerance, and transporting phytohormones (Yazaki, 2005; Rea, 2007; Yazaki et al, 2009; Kang et al, 2010). Recent literature has reported that some ABC transporters are involved in the secretion of compounds by roots (Badri et al, 2008, 2009)
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