Effects of appropriate low-temperature treatment on the yield and quality of pigmented potato (Solanum tuberosum L.) tubers

Temperature is one of the important environmental factors affecting plant growth, yield and quality. Moreover, appropriately low temperature is also beneficial for tuber coloration. The red potato variety Jianchuanhong, whose tuber color is susceptible to temperature, and the purple potato variety Huaxinyangyu, whose tuber color is stable, were used as experimental materials and subjected to 20 °C (control check), 15 °C and 10 °C treatments during the whole growth period. The effects of temperature treatment on the phenotype, the expression levels of structural genes related to anthocyanins and the correlations of each indicator were analyzed. The results showed that treatment at 10 °C significantly inhibited the potato plant height, and the chlorophyll content and photosynthetic parameters in the leaves were reduced, and the enzyme activities of SOD and POD were significantly increased, all indicating that the leaves were damaged. Treatment at 10 °C also affected the tuberization of Huaxinyangyu and reduced the tuberization and coloring of Jianchuanhong, while treatment at 15 °C significantly increased the stem diameter, root-to-shoot ratio, yield and content of secondary metabolites, especially anthocyanins. Similarly, the expression of structural genes were enhanced in two pigmented potatoes under low-temperature treatment conditions. In short, proper low temperature can not only increase yield but also enhance secondary metabolites production. Previous studies have not focused on the effects of appropriate low-temperature treatment during the whole growth period of potato on the changes in metabolites during tuber growth and development, these results can provide a theoretical basis and technical guidance for the selection of pigmented potatoes with better nutritional quality planting environment and the formulation of cultivation measures.

Integrated metabolome and transcriptome analyses of anthocyanin biosynthesis reveal key candidate genes involved in colour variation of Scutellaria baicalensis flowers

BACKGROUND

Bright flower colour assists plants attract insects to complete pollination and provides distinct ornamental values. In some medicinal plants, diverse flower colour variations usually imply differences in active ingredients. Compared to the common bluish purple of Scutellaria baicalensis flower (SB), the natural variants present rose red (SR) and white (SW) flowers were screened out under the same growing conditions in the genuine producing area Shandong Province, China. However, the mechanism of flower colour variation in S. baicalensis was remain unclear. In the present study, we conducted integrated transcriptome and metabolome analyses to uncover the metabolic difference and regulation mechanism in three S. baicalensis flowers.

RESULTS

The results showed that 9 anthocyanins were identified. Among which, 4 delphinidin-based anthocyanins were only detected in SB, 4 cyanidin-based anthocyanins (without cyanidin-3-O-glucoside) mainly accumulated in SR, and no anthocyanin but high level of flavanone, naringenin, was detected in SW. The gene expression profile indicated that the key structural genes in the flavonoid and anthocyanin biosynthesis pathway differentially expressed in flowers with different colours. Compared to SB, the down-regulated expression of F3'5'H, ANS, and 3GT gene in SR might influence the anthocyanin composition. Especially the InDel site with deletion of 7 nucleotides (AATAGAG) in F3'5'H in SR might be the determinant for lack of delphinidin-based anthocyanins in rose red flowers. In SW, the lower expression levels of DFR and two F3H genes might reduce the anthocyanin accumulation. Notably the SNP site of G > A mutation in the splicing site of DFR in SW might block anthocyanin biosynthesis from flavanones and thus cause white flowers. In addition, several key transcription factors, including MYB, bHLH, and NAC, which highly correlated with structural gene expression and anthocyanin contents were also identified.

CONCLUSIONS

These results provide clues to uncover the molecular regulatory mechanism of flower colour variation in S. baicalensis and promote novel insights into understanding the anthocyanin biosynthesis and regulation.

Hierarchical transcription factor and regulatory network for drought response in Betula platyphylla

Although many genes and biological processes involved in abiotic stress response have been identified, how they are regulated remains largely unclear. Here, to study the regulatory mechanism of birch (Betula platyphylla) responding to drought induced by polyethylene glycol (PEG) 6000 (20%, w/v), a partial correlation coefficient-based algorithm for constructing gene regulatory network (GRN) was proposed, and a three-layer hierarchical GRN was constructed, including 68 transcription factors (TFs), and 252 structural genes. Totally, 1448 predicted regulatory relationships are included, and most of them are novel. The reliability of GRN was verified by ChIP-PCR and qRT-PCR based on transient transformation. About 55% of genes in the bottom layer of GRN could confer drought tolerance. We selected the two TFs, BpMADS11 and BpNAC090, from the up layer and characterized their function in drought tolerance. Overexpression of BpMADS11 and BpNAC090 both reduces electrolyte leakage, ROS and MDA contents, displaying increased drought tolerance than wild-type birch. According to this GRN, the important biological processes involved in drought were identified, including "signaling hormone pathways", "water transport", "regulation of stomatal movement" and "response to oxidative stress". This work indicated that BpERF017, BpAGL61 and BpNAC090 are the key upstream regulators in birch drought tolerance. Our data clearly revealed the upstream regulators and TF-DNA interaction regulate different biological processes to adapt drought stress.

Purple-grained barley (Hordeum vulgare L.): marker-assisted development of NILs for investigating peculiarities of the anthocyanin biosynthesis regulatory network

BACKGROUND

Anthocyanins are plants secondary metabolites important for plant adaptation to severe environments and potentially beneficial to human health. Purple colour of barley grain is caused by the pigments synthesized in pericarp. One or two genes determine the trait. One of them is Ant2 mapped on chromosome 2HL and is known to encode transcription factor (TF) with a bHLH domain. In plants, bHLH regulates anthocyanin biosynthesis together with TF harboring an R2R3-MYB domain. In wheat, the R2R3-MYBs responsible for purple colour of grain pericarp are encoded by the homoallelic series of the Pp-1 genes that were mapped on the short arms of chromosomes 7. In barley, in orthologous positions to wheat's Pp-1, the Ant1 gene determining red colour of leaf sheath has been mapped. In the current study, we tested whether Ant1 has pleiotropic effect not only on leaf sheath colour but also on pericarp pigmentation.

RESULTS

А set of near isogenic lines (NILs) carrying different combinations of alleles at the Ant1 and Ant2 loci was created using markers-assisted backcrossing approach. The dominant alleles of both the Ant1 and Ant2 genes are required for anthocyanin accumulation in pericarp. A qRT-PCR analysis of the Ant genes in lemma and pericarp of the NILs revealed that some reciprocal interaction occurs between the genes. Expression of each of the two genes was up-regulated in purple-grained line with dominant alleles at the both loci. The lines carrying dominant allele either in the Ant1 or in the Ant2 locus were characterized by the decreased level of expression of the dominant gene and scant activity of the recessive one. The Ant1 and Ant2 expression was barely detected in uncolored line with recessive alleles at both loci. The anthocyanin biosynthesis structural genes were differently regulated: Chs, Chi, F3h, Dfr were transcribed in all lines independently on allelic state of the Ant1 and Ant2 genes, whereas F3'h and Ans were activated in presence on dominant alleles of the both regulatory genes.

CONCLUSIONS

The R2R3-MYB-encoding counterpart (Ant1) of the regulatory Ant2 gene was determined for the first time. The dominant alleles of both of them are required for activation of anthocyanin synthesis in barley lemma and pericarp. The R2R3-MYB + bHLH complex activates the synthesis via affecting expression of the F3'h and Ans structural genes. In addition, positive regulatory loop between Ant1 and Ant2 was detected. Earlier the interaction between the anthocyanin biosynthesis regulatory genes has been revealed in dicot plant species only. Our data demonstrated that the regulatory mechanism is considered to be more common for plant kingdom than it has been reported so far.

Upregulated structural and regulatory genes involved in anthocyanin biosynthesis for coloration of purple grains during the middle and late grain-filling stages

Anthocyanin biosynthesis is controlled by structural and regulatory genes. Purple wheat grains accumulate anthocyanin during developmental processes. However, anthocyanin cannot accumulate at the beginning of grain formation. To understand the reason for this phenomenon, we performed observations and analyses of pigments, developmental stages, and the transcriptome of caryopsis in Triticum aestivum L. cv. Guizi 1 (GZ1). In the early grain-filling stage (10 dpa to 20 dpa), anthocyanin accumulated from nearly 0 mg·kg^-1 (10 dpa) to 15.39 mg·kg^-1 (20 dpa), and the expression levels of structural genes (except GzDFR) and main regulatory genes GzMYB-7D1 and GzMYC-2A1 were low. When the grains developed to the middle (20 dpa to 30 dpa) and late (30 dpa to 40 dpa) grain-filling stages, the anthocyanin content peaked at 197.31 mg·kg^-1, and the expression levels of structural and regulatory genes at 25 dpa and 35 dpa were higher than that at 10 dpa. In particular, the expression levels of GzANS, Gz3GT, GzMYB-7D1, and GzMYC-2A1 were upregulated 45.74˜28.54, 765.00˜384.00, 419.00˜574.00, and 5.34˜29.05 times, respectively. Grains were also colored from green to purple. Anthocyanin accumulates in the pericarp and testa and is stored in vacuoles of epidermal and transverse cells. The major compositions are cyanidin and peonidin. These results revealed that the upregulated structural and regulatory genes in the middle and late grain-filling stages may result in the anthocyanin biosynthesis and coloration of grains, which provides new insights into anthocyanin biosynthesis and regulation mechanisms.