Two homeologous MATE transporter genes, NtMATE21 and NtMATE22, are involved in the modulation of plant growth and flavonol transport in Nicotiana tabacum

Integrated metabolomic and transcriptomic analyses reveal anthocyanin biosynthesis mechanisms and the regulatory role of LjAN2 in Lonicera japonica

Lonicera japonica flowers are a very commonly used traditional Chinese herb. Anthocyanins are the source of flower pigments, and also are renowned for their therapeutic activities. However, the specific anthocyanin composition and regulatory mechanisms governing their accumulation in L. japonica varieties remain unclear. Here, we first investigated the changes in flower color and anthocyanin content during development in the green flower (GFLJ) and the purple flower (PFLJ) cultivars of L. japonica. Results show GFLJ has green flowers and PFLJ has purple flowers, which are especially remarkable during S3-S4 stages. Accordingly, PFLJ had much higher (>10 times) anthocyanins contents at all the six flower stages than those of GFLJ. Further metabolomic analysis in S3 stage flowers found that most anthocyanins showed increased accumulation, whereas flavones and flavonols showed decreased accumulation in PFLJ compared to GFLJ. Transcriptome analysis identified 21 (85.7 % upregulated) anthocyanin synthase gene DEGs, and 23 MYB transcription factor (TF) DEGs (play essential roles in regulating anthocyanin biosynthesis). In addition, 19 GST and 14 MATE DEGs (play key roles in anthocyanins accumulation) were identified. Further, we found a novel MYB TF (LjAN2) that showed much higher expression in PFLJ. LjAN2 overexpression in tobacco led to purple leaves, and the upregulation of anthocyanin synthase genes (NtCHS and NtANS), as well as increased anthocyanin accumulation. This research offers a comprehensive understanding of the molecular basis of anthocyanin biosynthesis in L. japonica, highlighting its potential applications in the pharmaceutical industry.

MATE transporter OsMATE2 mediates root growth, grain size and weight by interacting with Mn-SOD and PABP in rice

Multidrug and toxic compound extrusion proteins (MATE) can transport small organic molecules in and out of cells and participate in detoxification, nutrient absorption, disease resistance and plant development processes. These compounds are widely distributed in plants. However, the mechanism by which MATE affects grain development remains elusive. In this study, we studied a MATE transporter, OsMATE2, which localized on the membrane. The CRISPR-Cas9 (CR) knockout line of OsMATE2 presented obvious decreases in grain weight. In addition, root development was also affected. Two proteins that interact with OsMATE2, namely, manganese-superoxide dismutase (Mn-SOD) and poly(A)-binding protein (PABP), were identified from a screening of yeast library. The results were validated through yeast two-hybrid and bimolecular fluorescence complementation experiments. The CRISPR-Cas9 (CR) knockout lines of Mn-SOD and PABP presented increased grain size and weight. Our findings demonstrated that OsMATE2 interacts with Mn-SOD and PABP to regulate grain development in rice.

DkDTX1/MATE1 mediates the accumulation of proanthocyanidin and affects astringency in persimmon

Proanthocyanidins (PAs) is a kind of polyphenols widely distributed in plants, and their astringent properties can protect plants from herbivores and regulate fruit taste. There is a great difference in PA composition between astringent (A)-type and nonastringent (NA)-type persimmon. Here, we studied the potential of DkDTX1/MATE1 in regulating PAs composition through its preferred transport in persimmon fruit. The results of fluorescence microscope showed that the DkDTX1/MATE1 green fluorescence overlapped with the blue light emitted by PA. Overexpression of DkDTX1/MATE1 in persimmon leaves not only significantly increase the concentrations of PA, but also upregulated the expression of PA biosynthesis pathway genes. Further overexpression of DkDTX1/MATE1 in persimmon fruit discs and stable genetic transformation of DkDTX1/MATE1 also led to PA concentrations increased. Molecular docking and transporter assays showed that DkDTX1/MATE1 preferentially transported catechin, epicatechin gallate and epigallocatechin gallate. DkDTX1/MATE1 mainly bound to the PA precursors via serine at position 68. Our findings indicate that DkDTX1/MATE1 play a role in the accumulation of PAs in early stage of fruit development and affects the astringency of persimmon through preferential transport PA precursors, which provided a theoretical basis for the future use of metabolic engineering to regulate the composition of PAs in persimmon.

The CaABCG14 transporter gene regulates the capsaicin accumulation in Pepper septum

Capsaicin (CAP), a crucial compound found in chili peppers, not only contributes to their spicy flavor but also possesses several industrial applications. CAP biosynthetic pathway is well known, while its transport mechanism remains elusive. Herein, we performed a comparative transcriptome analysis conducted on pepper fruit tissues at three different stages of development. Four important CAP transporter genes, including one MATE and three ABCs, were identified by differential expression and WGCNA analysis. Specifically, the expression patterns of three ABC genes were assessed in the septum of fruits from nine distinct genotypes of peppers with high capsaicin levels. Interestingly, CaABCG14 was associated with variations in CAP concentration and co-expressed with genes involved in CAP biosynthesis. Transient expression assay revealed that CaABCG14 is localized to the membrane and nucleus. Silencing of CaABCG14 resulted in a notable reduction in the levels of CAP contents and the expression of its biosynthetic genes in the septum of pepper. The overexpression of CaABCG14 greatly intensified the cytotoxic effects of CAP on the yeast cells. Taken together, we for the first time identified a new transporter gene CaABCG14, regulating the CAP accumulation in pepper septum. These findings offer a fresh molecular theoretical framework for CAP transport and accumulation.

Genome-wide analysis of Citrus medica ABC transporters reveals the regulation of fruit development by CmABCB19 and CmABCC10

ATP-binding cassette (ABC) transporters are vital for plant growth and development as they facilitate the transport of essential molecules. Despite the family's significance, limited information exists about its functional distinctions in Citrus medica. Our study identified 119 genes encoding ABC transporter proteins in the C. medica genome. Through an evolutionary tree and qPCR analysis, two ABC genes, CmABCB19 and CmABCC10, were implicated in C. medica fruit development, showing upregulation in normal fruits compared to malformed fruits. CmABCB19 was found to localize to the plasma membrane of Nicotiana tabacum, exhibiting indole-3-acetic acid (IAA) efflux activity in the yeast mutant strain yap1. CmABCC10, a tonoplast-localized transporter, exhibited efflux of diosmin, nobiletin, and naringin, with rutin influx in strain ycf1. Transgenic expression of CmABCB19 and CmABCC10 in Arabidopsis thaliana induced alterations in auxin and flavonoid content, impacting silique and seed size. This effect was attributed to the modulation of structural genes in the auxin biosynthesis (YUC5/9, CYP79B2, CYP83B1, SUR1) and flavonoid biosynthesis (4CL2/3, CHS, CHI, FLS1/3) pathways. In summary, the functional characterization of CmABCB19 and CmABCC10 illuminates auxin and flavonoid transport, offering insights into their interplay with biosynthetic pathways and providing a foundation for understanding the transporter's role in fruit development.

Comprehensive Identification and Expression Analysis of the Multidrug and Toxic Compound Extrusion (MATE) Gene Family in Brachypodium distachyon

The Multidrug and Toxic Compound Extrusion (MATE) proteins serve as pivotal transporters responsible for the extrusion of metabolites, thereby playing a significant role in both plant development and the detoxification of toxins. The MATE gene family within the Brachypodium distachyon, which is an important model organism of the Poaceae family, remains largely unexplored. Here, a comprehensive identification and analysis of MATE genes that complement B. distachyon were conducted. The BdMATE genes were systematically categorized into five distinct groups, predicated on an assessment of their phylogenetic affinities and protein structure. Furthermore, our investigation revealed that dispersed duplication has significantly contributed to the expansion of the BdMATE genes, with tandem and segmental duplications showing important roles, suggesting that the MATE genes in Poaceae species have embarked on divergent evolutionary trajectories. Examination of ω values demonstrated that BdMATE genes underwent purifying selection throughout the evolutionary process. Furthermore, collinearity analysis has confirmed a high conservation of MATE genes between B. distachyon and rice. The cis-regulatory elements analysis within BdMATEs promoters, coupled with expression patterns, suggests that BdMATEs play important roles during plant development and in response to phytohormones. Collectively, the findings presented establish a foundational basis for the subsequent detailed characterization of the MATE gene family members in B. distachyon.

Four glycosyltransferase genes are responsible for synthesis and accumulation of different flavonol glycosides in apple tissues

Flavonols are widely synthesized throughout the plant kingdom, playing essential roles in plant physiology and providing unique health benefits for humans. Their glycosylation plays significant role in improving their stability and solubility, thus their accumulation and function. However, the genes encoding the enzymes catalyze this glycosylation remain largely unknown in apple. This study utilized a combination of methods to identify genes encoding such enzymes. Initially, candidate genes were selected based on their potential to encode UDP-dependent glycosyltransferases (UGTs) and their expression patterns in response to light induction. Subsequently, through testing the in vitro enzyme activity of the proteins produced in Escherichia coli cells, four candidates were confirmed to encode a flavonol 3-O-galactosyltransferase (UGT78T6), flavonol 3-O-glucosyltransferase (UGT78S1), flavonol 3-O-xylosyltransferase/arabinosyltransferase (UGT78T5), and flavonol 3-O-rhamnosyltransferase (UGT76AE22), respectively. Further validation of these genes' functions was conducted by modulating their expression levels in stably transformed apple plants. As anticipated, a positive correlation was observed between the expression levels of these genes and the content of specific flavonol glycosides corresponding to each gene. Moreover, overexpression of a flavonol synthase gene, MdFLS, resulted in increased flavonol glycoside content in apple roots and leaves. These findings provide valuable insights for breeding programs aimed at enriching apple flesh with flavonols and for identifying flavonol 3-O-glycosyltransferases of other plant species.

Transcriptional regulation of flavonol biosynthesis in plants

Flavonols are a class of flavonoids that play a crucial role in regulating plant growth and promoting stress resistance. They are also important dietary components in horticultural crops due to their benefits for human health. In past decades, research on the transcriptional regulation of flavonol biosynthesis in plants has increased rapidly. This review summarizes recent progress in flavonol-specific transcriptional regulation in plants, encompassing characterization of different categories of transcription factors (TFs) and microRNAs as well as elucidation of different transcriptional mechanisms, including direct and cascade transcriptional regulation. Direct transcriptional regulation involves TFs, such as MYB, AP2/ERF, and WRKY, which can directly target the key flavonol synthase gene or other early genes in flavonoid biosynthesis. In addition, different regulation modules in cascade transcriptional regulation involve microRNAs targeting TFs, regulation between activators, interaction between activators and repressors, and degradation of activators or repressors induced by UV-B light or plant hormones. Such sophisticated regulation of the flavonol biosynthetic pathway in response to UV-B radiation or hormones may allow plants to fine-tune flavonol homeostasis, thereby balancing plant growth and stress responses in a timely manner. Based on orchestrated regulation, molecular design strategies will be applied to breed horticultural crops with excellent health-promoting effects and high resistance.

Preferential transport activity of DkDTX5/MATE5 affects the formation of different astringency in persimmon

Proanthocyanidins (PAs) are specialized metabolites that influence persimmon fruit quality. Normal astringent (A)-type and non-astringent (NA)-type mutants show significant variation in PA accumulation, but the influencing mechanism remains unclear. In this study, among the six identified DTXs/MATEs proteins associated with PA accumulation, we observed that allelic variation and preferential transport by DkDTX5/MATE5 induced variation in PA accumulation for A-type and NA-type fruit. The expression pattern of DkDTX5/MATE5 was correlated with PA accumulation in NA-type fruit. Upregulation and downregulation of DkDTX5/MATE5 promoted and inhibited PA accumulation, respectively, in the NA-type fruit. Interestingly, transporter assays of Xenopus laevis oocytes indicated that DkDTX5/MATE5 preferentially transported the PA precursors catechin, epicatechin, and epicatechin gallate, resulting in their increased ratios relative to the total PAs, which was the main source of variation in PA accumulation between the A-type and NA-type. The allele lacking Ser-84 in DkDTX5/MATE5 was identified as a dominantly expressed gene in the A-type and lost its transport function. Site-directed mutagenesis revealed that DkDTX5/MATE5 binds to PA precursors via Ser-84. These findings clarify the association between the transporter function of DkDTX5/MATE5 and PA variation, and can contribute to the breeding of new cultivars with improved fruit quality.

MINI BODY1, encoding a MATE/DTX family transporter, affects plant architecture in mungbean (Vigna radiata L.)

It has been shown that multidrug and toxic compound extrusion/detoxification (MATE/DTX) family transporters are involved in the regulation of plant development and stress response. Here, we characterized the mini body1 (mib1) mutants in mungbean, which gave rise to increased branches, pentafoliate compound leaves, and shortened pods. Map-based cloning revealed that MIB1 encoded a MATE/DTX family protein in mungbean. qRT-PCR analysis showed that MIB1 was expressed in all tissues of mungbean, with the highest expression level in the young inflorescence. Complementation assays in Escherichia coli revealed that MIB1 potentially acted as a MATE/DTX transporter in mungbean. It was found that overexpression of the MIB1 gene partially rescued the shortened pod phenotype of the Arabidopsis dtx54 mutant. Transcriptomic analysis of the shoot buds and young pods revealed that the expression levels of several genes involved in the phytohormone pathway and developmental regulators were altered in the mib1 mutants. Our results suggested that MIB1 plays a key role in the control of plant architecture establishment in mungbean.