Root restriction affected anthocyanin composition and up-regulated the transcription of their biosynthetic genes during berry development in ‘Summer Black’ grape

Root restriction was applied to ‘Summer black’ grape (Vitis vinifera L. × Vitis labrusca L.) to investigate its effect on anthocyanin biosynthesis in grape berry during development. Anthocyanin composition and expression patterns of 16 genes in anthocyanin pathway were thus analyzed. The results showed that the anthocyanin levels in berry skin were significantly increased and the anthocyanin profile was enriched. Gene expression pattern revealed that the increased anthocyanins coincide with the up-regulated expression of all 16 genes investigated, including phenylalanine ammonia-lyase, 4-coumarate CoA ligase, chalcone synthase 1, chalcone synthase 2, chalcone synthase 3, chalcone isomerase, flavanone 3-hydroxylase 1, flavanone 3-hydroxylase 2, flavonoid 3′-hydroxylase (F3′H), flavonoid 3′,5′-hydroxylase (F3′5′H), di-hydroflavonol 4-reductase, leucoanthocyanidin dioxygenase, O-methyltransferases (OMT), UDP-glucose:flavonoid 3-O-glucosyl-transferase (3GT), UDP-glucose:flavonoid 5-O-glucosyl-transferase (5GT) and glutathione S-transferase (GST). The increased total anthocyanins predominantly resulted from the increase of tri-hydroxylated, methoxylated and mono-glycosylated rather than di-hydroxylated, non-methoxylated, and di-glycosylated forms, which might be due to the differential regulation of F3′5′H/F3′H, OMT and 3GT, respectively.     

Identification and functional analysis of anthocyanin biosynthesis genes in <Emphasis Type="Italic">Phalaenopsis</Emphasis> hybrids

Phalaenopsis species are among the most popular potted flowers for their fascinating flowers. When their whole-genome sequencing was completed, they have become useful for studying the molecular mechanism of anthocyanin biosynthesis. Here, we identified 49 candidate anthocyanin synthetic genes in the Phalaenopsis genome. Our results showed that duplication events might contribute to the expansion of some gene families, such as the genes encoding chalcone synthase (PeCHS), flavonoid 3′-hydroxylase (PeF3′H), and myeloblastosis (PeMYB). To elucidate their functions in anthocyanin biosynthesis, we conducted a global expression analysis. We found that anthocyanin synthesis occurred during the very early flower development stage and that the flavanone 3-hydroxylase (F3H), F3′H, and dihydroflavonol 4-reductase (DFR) genes played key roles in this process. Over-expression of Phalaenopsis flavonoid 3′,5′-hydroxylase (F3′5′H) in petunia showed that it had no function in anthocyanin production. Furthermore, global analysis of sequences and expression patterns show that the regulatory genes are relatively conserved and might be important in regulating anthocyanin synthesis through different combined expression patterns. To determine the functions of MYB2, 11, and 12, we over-expressed them in petunia and performed yeast two-hybrid analysis with anthocyanin (AN)1 and AN11. The MYB2 protein had strong activity in regulating anthocyanin biosynthesis and induced significant pigment accumulation in transgenic plant petals, whereas MYB11 and MYB12 had lower activities. Our work provided important improvement in the understanding of anthocyanin biosynthesis and established a foundation for floral colour breeding in Phalaenopsis through genetic engineering.     

Anthocyanin biosynthetic genes in Brassica rapa

Background

Anthocyanins are a group of flavonoid compounds. As a group of important secondary metabolites, they perform several key biological functions in plants. Anthocyanins also play beneficial health roles as potentially protective factors against cancer and heart disease. To elucidate the anthocyanin biosynthetic pathway in Brassica rapa, we conducted comparative genomic analyses between Arabidopsis thaliana and B. rapa on a genome-wide level.

Results

In total, we identified 73 genes in B. rapa as orthologs of 41 anthocyanin biosynthetic genes in A. thaliana. In B. rapa, the anthocyanin biosynthetic genes (ABGs) have expanded and most genes exist in more than one copy. The anthocyanin biosynthetic structural genes have expanded through whole genome and tandem duplication in B. rapa. More structural genes located upstream of the anthocyanin biosynthetic pathway have been retained than downstream. More negative regulatory genes are retained in the anthocyanin biosynthesis regulatory system of B. rapa.

Conclusions

These results will promote an understanding of the genetic mechanism of anthocyanin biosynthesis, as well as help the improvement of the nutritional quality of B. rapa through the breeding of high anthocyanin content varieties.

Electronic supplementary material

The online version of this article (doi: 10.1186/1471-2164-15-426) contains supplementary material, which is available to authorized users.     

Effect of fruit maturity on UV-B-induced post-harvest anthocyanin accumulation in red Chinese sand pear

The effect of fruit maturity on UV-B-induced post-harvest anthocyanin accumulation in red Chinese sand pear (Pyrus pyrifolia Nakai) cultivar ‘Mantianhong’ was evaluated. During the irradiation, compared with the fruit harvested at 20 days before harvest (DBH) and 10 DBH, the mature fruit (harvested at commercial harvest date) had higher soluble solids content, soluble sugars concentration but lower firmness and starch content. In addition, higher content of anthocyanin has been detected in mature fruits than in immature fruits due to the significant increase in the expression of genes related to anthocyanin biosynthesis, especially PpCHS, PpF3H, PpANS, PpUFGT, PyMYB10 and PpbHLH in red Chinese sand pears. Hierarchical clustering analysis suggested that most genes related to anthocyanin biosynthesis showed a coordinate expression pattern. These findings are helpful in understanding the molecular mechanism of anthocyanin biosynthesis and regulation, which could lead to the development of new technologies for improving fruit color in Chinese sand pears and other fruits.     

Analysis of Functions of VIP1 and Its Close Homologs in Osmosensory Responses of Arabidopsis thaliana

VIP1 is a bZIP protein in Arabidopsis thaliana. VIP1 accumulates in the nucleus under hypo-osmotic conditions and interacts with the promoters of hypo-osmolarity-responsive genes, CYP707A1 and CYP707A3 (CYP707A1/3), but neither overexpression of VIP1 nor truncation of its DNA-binding region affects the expression of CYP707A3 in vivo, raising the possibility that VIP and other proteins are functionally redundant. Here we show further analyses on VIP1 and its close homologs, namely, Arabidopsis group I bZIP proteins. The patterns of the signals of the GFP-fused group I bZIP proteins were similar in onion and Arabidopsis cells, suggesting that they have similar subcellular localization. In a yeast one-hybrid assay, the group I bZIP proteins caused reporter gene activation in the yeast reporter strain. VIP1 and other group I bZIP proteins showed positive results in a yeast two-hybrid assay and a bimolecular fluorescence complementation assay, suggesting that they physically interact. These results support the idea that they have somewhat similar functions. By gel shift assays, VIP1-binding sequences in the CYP707A1/3 promoters were confirmed to be AGCTGT/G. Their presence in the promoters of the genes that respond to hypo-osmotic conditions was evaluated using previously published microarray data. Interestingly, a significantly higher proportion of the promoters of the genes that were up-regulated by rehydration treatment and/or submergence treatment (treatment by a hypotonic solution) and a significantly lower proportion of the promoters of the genes that were down-regulated by such treatment shared AGCTGT/G. To further assess the physiological role of VIP1, constitutively nuclear-localized variants of VIP1 were generated. When overexpressed in Arabidopsis, some of them as well as VIP1 caused growth retardation under a mannitol-stressed condition, where VIP1 is localized mainly in the cytoplasm. This raises the possibility that the expression of VIP1 itself rather than its nuclear localization is responsible for regulating the mannitol responses.     

Functional characterization of key structural genes in rice flavonoid biosynthesis

Rice is a model system for monocot but the molecular features of rice flavonoid biosynthesis have not been extensively characterized. Rice structural gene homologs encoding chalcone synthase (CHS), chalcone isomerase (CHI), flavanone 3-hydroxylase (F3H), flavonoid 3′-hydroxylase (F3′H), dihydroflavonol 4-reductase (DFR), and anthocyanidin synthase (ANS) were identified by homology searches. Unique differential expression of OsF3H, OsDFR, and OsANS1 controlled by the Pl ^w locus, which contains the R/B-type regulatory genes OSB1 and OSB2, was demonstrated during light-induced anthocyanin accumulation in T65-Plw seedlings. Previously, F3H genes were often considered as early genes co-regulated with CHS and CHI genes in other plants. In selected non-pigmented rice lines, OSB2 is not expressed following illumination while their expressed OSB1sequences all contain the same nucleotide change leading to the T⁶⁴ M substitution within the conserved N-terminal interacting domain. Furthermore, the biochemical roles of the expressed rice structural genes (OsCHS1, OsCHI, OsF3H, and OsF3′H) were established in planta for the first time by complementation in the appropriate Arabidopsis transparent testa mutants. Using yeast two-hybrid analysis, OsCHS1 was demonstrated to interact physically with OsF3H, OsF3′H, OsDFR, and OsANS1, suggesting the existence of a macromolecular complex for anthocyanin biosynthesis in rice. Finally, flavones were identified as the major flavonoid class in the non-pigmented T65 seedlings in which the single-copy OsF3H gene was not expressed. Competition between flavone and anthocyanin pathways was evidenced by the significant reduction of tricin accumulation in the T65-Plw seedlings. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.