Quantification of Tissue Specific Expression of ABC type B transporters in Eschscholzia californica

Abstract

Adenosine triphosphate (ATP)-binding cassette (ABC) transporters are a diverse superfamily of transmembrane proteins found in all eukaryotes. These proteins couple the hydrolysis of ATP to the transport of a wide variety of substrates across cellular membranes. In plants, ABC type B (ABCB) transporters have been shown to be involved in the transport of both growth regulators (auxin) and secondary metabolites. Plant secondary metabolism refers to the vast array of small molecules being produced, but not directly required for plant growth and development. However, secondary metabolites have been shown to play important roles in plant defense, such as in deterring herbivory or resistance to pathogens. It has been shown that transport between cell types is necessary in the biosynthesis of many of these metabolites and that ABC transporters play a necessary role in this trafficking. Eschscholzia californica, or the California poppy, accumulates alkaloids within specialized cells within roots. Our lab previously identified EcABCB1, a transporter involved in the transport of these alkaloids. In this project, using the recently-released draft genome of E. californica, we have identified seven additional putative ABCB transporters (ABCB2-7). Using quantitative polymerase chain reaction (qPCR), we will quantify their expression profiles in a tissue-specific manner. These results will then be used to draw inferences of the function of each candidate gene, based on comparative analysis of expression profiles of ABCB homologs in Arabidopsis thaliana. Preliminary data shows that EcABCB1 is expressed in both roots and stems, whereas EcABCB2 is expressed ubiquitously across all tissues. This may indicate that EcABCB2 may be involved in the transport a growth factor such as auxin, which is a metabolite necessary for growth across all organs. In order to obtain a better understanding of the biochemistry of plants and the synthesis of their alkaloids, the transporters required for this synthesis must be characterized.

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