<Li> ABC (ATP binding cassette) transporter: MDR, CFTR, etc . </Li> <P> Adenosine Triphosphate - binding cassette transporters (ABC transporters) comprise a large and diverse protein family, often functioning as ATP - driven pumps . Usually, there are several domains involved in the overall transporter protein's structure, including two nucleotide - binding domains that constitute the ATP - binding motif and two hydrophobic transmembrane domains that create the "pore" component . In broad terms, ABC transporters are involved in the import or export of molecules across a cell membrane; yet within the protein family there is an extensive range of function . </P> <P> In plants, ABC transporters are often found within cell and organelle membranes, such as the mitochondria, chloroplast, and plasma membrane . There is evidence to support that plant ABC transporters play a direct role in pathogen response, phytohormone transport, and detoxification . Furthermore, certain plant ABC transporters may function in actively exporting volatile compounds and antimicrobial metabolites . </P> <P> In petunia flowers (Petunia hybrida), the ABC transporter PhABCG1 is involved in the active transport of volatile organic compounds . PhABCG1 is expressed in the petals of open flowers . In general, volatile compounds may promote the attraction of seed - dispersal organisms and pollinators, as well as aid in defense, signaling, allelopathy, and protection . To study the protein PhABCG1, transgenic petunia RNA interference lines were created with decreased PhABCG1 expression levels . In these transgenic lines, a decrease in emission of volatile compounds was observed . Thus, PhABCG1 is likely involved in the export of volatile compounds . Subsequent experiments involved incubating control and transgenic lines that expressed PhABCG1 to test for transport activity involving different substrates . Ultimately, PhABCG1 is responsible for the protein - mediated transport of volatile organic compounds, such as benezyl alcohol and methylbenzoate, across the plasma membrane . </P>

Symport active transporters move two substances across the membrane in the same direction