Involvement of LeMRP, an ATP-binding cassette transporter, in shikonin transport and biosynthesis in Lithospermum erythrorhizon

Enhancing rutin accumulation in Tartary buckwheat through a novel flavonoid transporter protein FtABCC2

Tartary buckwheat (Fagopyrum tataricum) is an annual coarse cereal from the Polygonaceae family, known for its high content of flavonoid compounds, particularly rutin. But so far, the mechanisms of the flavonoid transport and storage in Tartary buckwheat (TB) remain largely unexplored. This study focuses on ATP-binding cassette transporters subfamily C (ABCC) members, which are crucial for the biosynthesis and transport of flavonoids in plants. The evolutionary and expression pattern analyses of the ABCC genes in TB identified an ABCC protein gene, FtABCC2, that is highly correlated with rutin synthesis. Subcellular localization analysis revealed that FtABCC2 protein is specifically localized to the vacuole membrane. Heterologous expression of FtABCC2 in Saccharomyces cerevisiae confirmed that its transport ability of flavonoid glycosides such as rutin and isoquercetin, but not the aglycones such as quercetin and dihydroquercetin. Overexpression of FtABCC2 in TB hairy root lines resulted in a significant increase in total flavonoid and rutin content (P < 0.01). Analysis of the FtABCC2 promoter revealed potential cis-acting elements responsive to hormones, cold stress, mechanical injury and light stress. Overall, this study demonstrates that FtABCC2 can efficiently facilitate the transport of rutin into vacuoles, thereby enhancing flavonoids accumulation. These findings suggest that FtABCC2 is a promising candidate for molecular-assisted breeding aimed at developing high-flavonoid TB varieties.

Inventory of ATP-binding cassette proteins in Lithospermum erythrorhizon as a model plant producing divergent secondary metabolites

ATP-binding cassette (ABC) proteins are the largest membrane transporter family in plants. In addition to transporting organic substances, these proteins function as ion channels and molecular switches. The development of multiple genes encoding ABC proteins has been associated with their various biological roles. Plants utilize many secondary metabolites to adapt to environmental stresses and to communicate with other organisms, with many ABC proteins thought to be involved in metabolite transport. Lithospermum erythrorhizon is regarded as a model plant for studying secondary metabolism, as cells in culture yielded high concentrations of meroterpenes and phenylpropanoids. Analysis of the genome and transcriptomes of L. erythrorhizon showed expression of genes encoding 118 ABC proteins, similar to other plant species. The number of expressed proteins in the half-size ABCA and full-size ABCB subfamilies was ca. 50% lower in L. erythrorhizon than in Arabidopsis, whereas there was no significant difference in the numbers of other expressed ABC proteins. Because many ABCG proteins are involved in the export of organic substances, members of this subfamily may play important roles in the transport of secondary metabolites that are secreted into apoplasts.

Transcriptome-based identification and expression characterization of RgABCC transporters in Rehmannia glutinosa

ABCC multidrug resistance-associated proteins (ABCCs/MRPs), a subfamily of ABC transporters, are involved in multiple physiological processes. Although these proteins have been characterized in some plants, limited efforts have been made to address their possible roles in Rehmannia glutinosa, a medicinal plant. Here, we scanned R. glutinosa transcriptome sequences and identified 18 RgABCC genes by in silico analysis. Sequence alignment revealed that the RgABCCs were closely phylogenetically related and highly conserved with other plant ABCCs/MRPs. Subcellular localization revealed that most of the RgABCCs were deposited in vacuoles and a few in plasma membranes. Tissue-specific expression of the RgABCCs indicated significant specific accumulation patterns, implicating their roles in the respective tissues. Differential temporal expression patterns of the RgABCCs exhibited their potential roles during root development. Various abiotic stress and hormone treatment experiments indicated that some RgABCCs could be transcriptionally regulated in roots. Furthermore, the transcription of several RgABCCs in roots was strongly activated by cadmium (Cd), suggesting possible roles under heavy metal stresses. Functional analysis of RgABCC1 heterologous expression revealed that it may increase the tolerance to Cd in yeast, implying its Cd transport activity. Our study provides a detailed inventory and molecular characterization of the RgABCCs and valuable information for exploring their functions in R. glutinosa.