Molecular mechanisms underlying natural deficient and ultraviolet-induced accumulation of anthocyanin in the peel of 'Jinxiu' peach.

Peach varieties that differ in red coloration due to varied anthocyanin accumulation result from transcriptional regulation by PpMYB10s, a group of specific R2R3 MYBs. Here we investigated the mechanisms driving a lack of anthocyanin in yellow-skinned 'Jinxiu' peach peel, as well as accumulation induced by UV irradiance. It was found that PpMYB10.1, PpMYB10.2 and PpMYB10.3 were positive regulators of anthocyanin accumulation, but the stimulation by PpMYB10.2 was weak. Low expression of PpMYB10.1 causes natural anthocyanin deficiency in 'Jinxiu' peel. However, the promoter sequences of PpMYB10.1 were identical in 'Jinxiu' and a naturally red-coloured peach 'Hujingmilu'. Therefore, potential negative regulator(s) upstream of PpMYB10.1 were explored. A novel R2R3-MYB repressor termed PpMYB80 was identified through comparative transcriptomic analysis and then functionally confirmed via transiently overexpressing and silencing in peach fruit, as well as transformation in tobacco. PpMYB80 directly binds to the promoter of PpMYB10.1 and inhibits its expression, but does not affect PpMYB10.3. In UV-exposed 'Jinxiu' fruit, expression of PpMYB10.3 was upregulated, while PpMYB10.1 remained low and PpMYB80 enhanced, which results in accumulation of anthocyanin in peel. This study revealed a transcriptional cascade involving PpMYB activators and repressors in regulating basal and UV-induced anthocyanin accumulation in peach peel.

An 'activator-repressor' loop controls the anthocyanin biosynthesis in red-skinned pear.

The color of red-skinned pear (Pyrus spp.) is primarily attributed to accumulation of anthocyanins, which provide nutritional benefits for human health and are closely associated with the commercial value of fruits. Here, we reported the functional characterization of a R2R3-MYB repressor PyMYB107, which forms an 'activator-repressor' loop to control anthocyanin accumulation in the red-skinned pear. PyMYB107 overexpression inhibited anthocyanin biosynthesis in both pear calli and fruits, while virus-induced gene silencing of PyMYB107 increased anthocyanin accumulation in pear fruits. Furthermore, ectopic expression of PyMYB107 decreased anthocyanin accumulation in tomato, strawberry and tobacco. PyMYB107 can competitively bind to PybHLH3 with PyMYB10/MYB114, thereby suppressing the transcriptional activation of key anthocyanin biosynthesis genes, PyANS and PyUFGT. Site-directed mutagenesis showed that mutations within the R3 domain and EAR motif of PyMYB107 eliminated its repressive activity. Additionally, PyMYB107 exhibited a comparable expression pattern to PyMYB10/MYB114 and was transcriptionally activated by them. Our finding advanced comprehension of the repression mechanism underlying anthocyanin accumulation, providing valuable molecular insights into improving quality of pear fruits.

The Response of Growth and Transcriptome Profiles of Tea Grey Blight Disease Pathogen Pestalotiopsis theae to the Variation of Exogenous L-Theanine.

Tea grey blight disease is one of the most destructive diseases that infects tea and is caused by the pathogen Pestalotiopsis theae (Sawada) Steyaert. L-theanine is a unique non-protein amino acid of the tea plant. Different concentrations of L-theanine exhibit significant inhibitory effects on the growth and sporulation ability of the pathogen causing tea grey blight disease. To understand the effect mechanism of L-theanine on P. theae, transcriptome profiling was performed on the pathogenic mycelium treated with three different concentrations of L-theanine: no L-theanine treatment (TH0), 20 mg/mL theanine treatment (TH2), and 40 mg/mL theanine treatment (TH4). The colony growths were significantly lower in the treatment with L-theanine than those without L-theanine. The strain cultured with a high concentration of L-theanine produced no spores or only a few spores. In total, 2344, 3263, and 1158 differentially expressed genes (DEGs) were detected by RNA-sequencing in the three comparisons, Th2 vs. Th0, Th4 vs. Th0, and Th4 vs. Th2, respectively. All DEGs were categorized into 24 distinct clusters. According to GO analysis, low concentrations of L-theanine primarily affected molecular functions, while high concentrations of L-theanine predominantly affected biological processes including external encapsulating structure organization, cell wall organization or biogenesis, and cellular amino acid metabolic process. Based on KEGG, the DEGs of Th2 vs. Th0 were primarily involved in pentose and glucuronate interconversions, histidine metabolism, and tryptophan metabolism. The DEGs of Th4 vs. Th0 were mainly involved in starch and sucrose metabolism, amino sugar, and nucleotide sugar metabolism. This study indicated that L-theanine has a significant impact on the growth and sporulation of the pathogen of tea grey blight disease and mainly affects amino acid metabolism, carbohydrate metabolism, and cellular structure-related biosynthesis processes of pathogenic fungi. This work provides insights into the direct control effect of L-theanine on pathogenic growth and also reveals the molecular mechanisms of inhibition of L-theanine to P. theae.

MYB transcription factors encoded by diversified tandem gene clusters cause varied Morella rubra fruit color.

Chinese bayberry (Morella rubra) is a fruit tree with a remarkable variation in fruit color, ranging from white to dark red as determined by anthocyanin content. In dark red "Biqi" (BQ), red "Dongkui" (DK), pink "Fenhong" (FH), and white "Shuijing" (SJ), we identified an anthocyanin-related MYB transcription factor-encoding gene cluster of four members, i.e. MrMYB1.1, MrMYB1.2, MrMYB1.3, and MrMYB2. Collinear analysis revealed that the MYB tandem cluster may have occurred in a highly conserved region of many eudicot genomes. Two alleles of MrMYB1.1 were observed; MrMYB1.1-1 (MrMYB1.1n) was a full-length allele and homozygous in "BQ", MrMYB1.1-2 (MrMYB1.1d) was a nonfunctional allele with a single base deletion and homozygous in "SJ", and MrMYB1.1n/MrMYB1.1d were heterozygous in "DK" and "FH". In these four cultivars, expression of MrMYB1.1, MrMYB1.2, and MrMYB2 was enhanced during ripening. Both alleles were equally expressed in MrMYB1.1n/MrMYB1.1d heterozygous cultivars as revealed by a cleaved amplified polymorphic sequence marker. Expression of MrMYB1.3 was restricted to some dark red cultivars only. Functional characterization revealed that MrMYB1.1n and MrMYB1.3 can induce anthocyanin accumulation while MrMYB1.1d, MrMYB1.2, and MrMYB2 cannot. DNA-protein interaction assays indicated that MrMYB1.1n and MrMYB1.3 can directly bind to and activate the promoters of anthocyanin-related genes via interaction with a MYC-like basic helix-loop-helix protein MrbHLH1. We concluded that the specific genotype of MrMYB1.1 alleles, as well as the exclusive expression of MrMYB1.3 in some dark red cultivars, contributes to fruit color variation. The study provides insights into the mechanisms for regulation of plant anthocyanin accumulation by MYB tandem clusters.

Allelic variation of BBX24 is a dominant determinant controlling red coloration and dwarfism in pear.

Variation in anthocyanin biosynthesis in pear fruit provides genetic germplasm resources for breeding, while dwarfing is an important agronomic trait, which is beneficial to reduce the management costs and allow for the implementation of high-density cultivation. Here, we combined bulked segregant analysis (BSA), quantitative trait loci (QTL), and structural variation (SV) analysis to identify a 14-bp deletion which caused a frame shift mutation and resulted in the premature translation termination of a B-box (BBX) family of zinc transcription factor, PyBBX24, and its allelic variation termed PyBBX24ΔN14. PyBBX24ΔN14 overexpression promotes anthocyanin biosynthesis in pear, strawberry, Arabidopsis, tobacco, and tomato, while that of PyBBX24 did not. PyBBX24ΔN14 directly activates the transcription of PyUFGT and PyMYB10 through interaction with PyHY5. Moreover, stable overexpression of PyBBX24ΔN14 exhibits a dwarfing phenotype in Arabidopsis, tobacco, and tomato plants. PyBBX24ΔN14 can activate the expression of PyGA2ox8 via directly binding to its promoter, thereby deactivating bioactive GAs and reducing the plant height. However, the nuclear localization signal (NLS) and Valine-Proline (VP) motifs in the C-terminus of PyBBX24 reverse these effects. Interestingly, mutations leading to premature termination of PyBBX24 were also identified in red sports of un-related European pear varieties. We conclude that mutations in PyBBX24 gene link both an increase in pigmentation and a decrease in plant height.

Integrative analysis of metabolome and transcriptome reveals a dynamic regulatory network of potato tuber pigmentation.

Potatoes consist of flavonoids that provide health benefits for human consumers. To learn more about how potato tuber flavonoid accumulation and flesh pigmentation are controlled, we analyzed the transcriptomic and metabolomic profile of potato tubers from three colored potato clones at three developmental phases using an integrated approach. From the 72 flavonoids identified in pigmented flesh, differential abundance was noted for anthocyanins, flavonols, and flavones. Weighted gene co-expression network analysis further allowed modules and candidate genes that positively or negatively regulate flavonoid biosynthesis to be identified. Furthermore, an R2R3-MYB repressor StMYB3 and an R3-MYB repressor StMYBATV involved in the modulation of anthocyanin biosynthesis during tuber development were identified. Both StMYB3 and StMYBATV could interact with the cofactor StbHLH1 and repress anthocyanin biosynthesis. Our results indicate a feedback regulatory mechanism of a coordinated MYB activator-repressor network on fine-tuning of potato tuber pigmentation during tuber development.

DNA methylation reprogramming provides insights into light-induced anthocyanin biosynthesis in red pear.

DNA methylation, an epigenetic mark, is proposed to regulate plant anthocyanin biosynthesis. It well known that light induces anthocyanin accumulation, with bagging treatments commonly used to investigate light-controlled anthocyanin biosynthesis. We studied the DNA methylome landscape during pear skin coloration under various conditions (fruits re-exposed to sunlight after bag removal). The DNA methylation level in gene body/TE and its flanking sequence was generally similar between debagged and bagged treatments, however differentially methylated regions (DMRs) were re-modelled after light-exposure. Both DNA demethylase homologs and the RNA-directed DNA methylation (RdDM) pathways contributed to this re-distribution. A total of 310 DEGs were DMR-associated during light-induced anthocyanin biosynthesis between debagged and bagged treatments. The hypomethylated mCHH context was seen within the promoter of PyUFGT, together with other anthocyanin biosynthesis genes (PyPAL, PyDFR and PyANS). This enhanced transcriptional activation and promoted anthocyanin accumulation after light re-exposure. Unlike previous reports on bud sports, we did not detect DMRs within the MYB10 promoter. Instead, we observed the genome-wide re-distribution of methylation patterns, suggesting different mechanisms underlying methylation patterns of differentially accumulated anthocyanins caused by either bud mutation or environment change. We investigate the dynamic landscape of genome-scale DNA methylation, which is the combined effect of DNA demethylation and RdDM pathway, in the process of light-induced fruit colour formation in pear. This process is regulated by methylation changes on promoter regions of several DEGs. These results provide a DMR-associated DEGs set and new insight into the mechanism of DNA methylation involved in light-induced anthocyanin biosynthesis.

Exogenous abscisic acid and sugar induce a cascade of ripening events associated with anthocyanin accumulation in cultured Pinot Noir grape berries.

Fruit quality is dependent on various factors including flavour, texture and colour. These factors are determined by the ripening process, either climacteric or non-climacteric. In grape berry, which is non-climacteric, the process is signalled by a complex set of hormone changes. Abscisic acid (ABA) is one of the key hormones involved in ripening, while sugar availability also plays a significant role in certain ripening aspects such as anthocyanin production. To understand the relative influence of hormone and sugar signalling in situ can prove problematic due to the physiological and environmental (abiotic and biotic) factors at play in vineyards. Here we report on the use of in vitro detached berry culture to investigate the comparative significance of ABA and sugar in the regulation of Pinot noir berry anthocyanin production under controlled conditions. Using a factorial experimental design, pre-véraison berries were cultured on media with various concentrations of sucrose and ABA. After 15 days of in vitro culture, the berries were analysed for changes in metabolites, hormones and gene expression. Results illustrated a stimulatory effect of sucrose and ABA on enhancing berry colour and a corresponding increase in anthocyanins. Increased ABA concentration was able to boost anthocyanin production in berries when sucrose supply was low. The sucrose and ABA effects on berry anthocyanins were primarily manifested through the up-regulation of transcription factors and other genes in the phenylpropanoid pathway, while in other parts of the pathway a down-regulation of key proanthocyanindin transcription factors and genes corresponded to sharp reduction in berry proanthocyanidins, irrespective of sucrose supply. Similarly, increased ABA was correlated with a significant reduction in berry malic acid and associated regulatory genes. These findings suggest a predominance of berry ABA over berry sugar in coordinating the physiological and genetic regulation of anthocyanins and proanthocyanins in Pinot noir grape berries.

Elevating fruit carotenoid content in apple (Malus x domestica Borkh).

Carotenoid compounds accumulate to confer coloration to plant tissues and have some established health benefits in humans. These pigments have antioxidant properties and are precursors of vitamin A, which is important for human vision. Apple is widely consumed globally, but most commercial apple cultivars have low fruit carotenoid content because these pigments accumulate mostly in the fruit skin rather than the flesh (the majority of the edible portion). Although carotenoids accumulate in the early stages of fruit development, much of this carotenoid is lost by fruit maturity as a result of low biosynthetic rate, rapid turnover of compounds and/or lack of storage capacity in these tissues. Improving apple fruit carotenoid content through traditional breeding or genetic technologies, will take a long time because of the extended juvenile phase of the trees and limited germplasm diversity within many commercial breeding programs. This process, however, can be accelerated by fundamental understanding of the apple carotenoid biosynthetic pathway and the mechanisms controlling the metabolic steps. The availability of a well annotated apple genome sequence has led to the identification of apple carotenoid gene families and potential transcription factors. This is an important step since the knowledge could be used to elevate carotenoid content either through breeding or genetic transformation techniques. Here, we provide an overview of carotenogenesis in apple and outline the methods employed to improve the carotenoid content of this horticultural crop.

The apple BTB protein MdBT2 positively regulates MdCOP1 abundance to repress anthocyanin biosynthesis.

The ubiquitin ligase CONSTITUTIVELY PHOTOMORPHOGENIC 1 (COP1) plays a central role in light-induced anthocyanin biosynthesis. However, the upstream regulatory factors of COP1 remain poorly understood, particularly in horticultural plants. Here, we identified an MdCOP1-interacting protein, BROAD-COMPLEX, TRAMTRACK AND BRIC A BRAC2 (MdBT2), in apple (Malus domestica). MdBT2 is a BTB protein that directly interacts with and stabilizes MdCOP1 by inhibiting self-ubiquitination. Fluorescence observation and cell fractionation assays showed that MdBT2 increased the abundance of MdCOP1 in the nucleus. Moreover, a series of phenotypic analyses indicated that MdBT2 promoted MdCOP1-mediated ubiquitination and degradation of the MdMYB1 transcription factor, inhibiting the expression of anthocyanin biosynthesis genes and anthocyanin accumulation. Overall, our findings reveal a molecular mechanism by which MdBT2 positively regulates MdCOP1, providing insight into MdCOP1-mediated anthocyanin biosynthesis.

The red flesh of kiwifruit is differentially controlled by specific activation-repression systems.

Anthocyanins are visual cues for pollination and seed dispersal. Fruit containing anthocyanins also appeals to consumers due to its appearance and health benefits. In kiwifruit (Actinidia spp.) studies have identified at least two MYB activators of anthocyanin, but their functions in fruit and the mechanisms by which they act are not fully understood. Here, transcriptome and small RNA high-throughput sequencing were used to comprehensively identify contributors to anthocyanin accumulation in kiwifruit. Stable overexpression in vines showed that both 35S::MYB10 and MYB110 can upregulate anthocyanin biosynthesis in Actinidia chinensis fruit, and that MYB10 overexpression resulted in anthocyanin accumulation which was limited to the inner pericarp, suggesting that repressive mechanisms underlie anthocyanin biosynthesis in this species. Furthermore, motifs in the C-terminal region of MYB10/110 were shown to be responsible for the strength of activation of the anthocyanic response. Transient assays showed that both MYB10 and MYB110 were not directly cleaved by miRNAs, but that miR828 and its phased small RNA AcTAS4-D4(-) efficiently targeted MYB110. Other miRNAs were identified, which were differentially expressed between the inner and outer pericarp, and cleavage of SPL13, ARF16, SCL6 and F-box1, all of which are repressors of MYB10, was observed. We conclude that it is the differential expression and subsequent repression of MYB activators that is responsible for variation in anthocyanin accumulation in kiwifruit species.

The genome of low-chill Chinese plum "Sanyueli" (Prunus salicina Lindl.) provides insights into the regulation of the chilling requirement of flower buds.

Chinese plum (Prunus salicina Lindl.) is a stone fruit that belongs to the Prunus genus and plays an important role in the global production of plum. In this study, we report the genome sequence of the Chinese plum "Sanyueli", which is known to have a low-chill requirement for flower bud break. The assembled genome size was 282.38 Mb, with a contig N50 of 1.37 Mb. Over 99% of the assembly was anchored to eight pseudochromosomes, with a scaffold N50 of 34.46 Mb. A total of 29,708 protein-coding genes were predicted from the genome and 46.85% (132.32 Mb) of the genome was annotated as repetitive sequence. Bud dormancy is influenced by chilling requirement in plum and partly controlled by DORMANCY ASSOCIATED MADS-box (DAM) genes. Six tandemly arrayed PsDAM genes were identified in the assembled genome. Sequence analysis of PsDAM6 in "Sanyueli" revealed the presence of large insertions in the intron and exon regions. Transcriptome analysis indicated that the expression of PsDAM6 in the dormant flower buds of "Sanyueli" was significantly lower than that in the dormant flower buds of the high chill requiring "Furongli" plum. In addition, PsDAM6 expression was repressed by chilling treatment. The genome sequence of "Sanyueli" plum provides a valuable resource for elucidating the molecular mechanisms responsible for the regulation of chilling requirements, and it is also useful for the identification of the genes involved in the control of other important agronomic traits and molecular breeding in plum.

Pear genetics: Recent advances, new prospects, and a roadmap for the future.

Pear, belonging to the genus Pyrus, is one of the most economically important temperate fruit crops. Pyrus is an important genus of the Rosaceae family, subfamily Maloideae, and has at least 22 different species with over 5000 accessions maintained or identified worldwide. With the release of draft whole-genome sequences for Pyrus, opportunities for pursuing studies on the evolution, domestication, and molecular breeding of pear, as well as for conducting comparative genomics analyses within the Rosaceae family, have been greatly expanded. In this review, we highlight key advances in pear genetics, genomics, and breeding driven by the availability of whole-genome sequences, including whole-genome resequencing efforts, pear domestication, and evolution. We cover updates on new resources for undertaking gene identification and molecular breeding, as well as for pursuing functional validation of genes associated with desirable economic traits. We also explore future directions for "pear-omics".

Identification of a Strong Anthocyanin Activator, VbMYBA, From Berries of Vaccinium bracteatum Thunb.

Wufanshu (Vaccinium bracteatum Thunb.), which is a wild member of the genus Vaccinium, accumulates high concentration of anthocyanin in its berries. In this study, the accumulated anthocyanins and their derivatives in Wufanshu berries were identified through UHPLC-MS/MS analysis. Candidate anthocyanin biosynthetic genes were identified from the transcriptome of Wufanshu berries. qRT-PCR analyses showed that the expression of anthocyanin structural genes correlated with anthocyanin accumulation in berries. The R2R3-MYB, VbMYBA, which is a homolog of anthocyanin promoting R2R3-MYBs from other Vaccinium species, was also identified. Transient expression of VbMYBA in Nicotiana tabacum leaves confirmed its role as an anthocyanin regulator, and produced a higher anthocyanin concentration when compared with blueberry VcMYBA expression. Dual-luciferase assays further showed that VbMYBA can activate the DFR and UFGT promoters from other Vaccinium species. VbMYBA has an additional 23 aa at the N terminus compared with blueberry VcMYBA, but this was shown not to affect the ability to regulate anthocyanins. Taken together, our results provide important information on the molecular mechanisms responsible for the high anthocyanin content in Wufanshu berries.

Competition between anthocyanin and kaempferol glycosides biosynthesis affects pollen tube growth and seed set of Malus.

Flavonoids play important roles in regulating plant growth and development. In this study, three kaempferol 3-O-glycosides were identified and mainly accumulated in flowers but not in leaves or fruits of Malus. In Malus, flower petal color is normally white, but some genotypes have red flowers containing anthocyanin. Anthocyanin biosynthesis appears to be in competition with kaempferol 3-O-glycosides production and controlled by the biosynthetic genes. The white flower Malus genotypes had better-developed seeds than the red flower genotypes. In flowers, the overexpression of MYB10 in Malus domestica enhanced the accumulation of anthocyanin, but decreased that of kaempferol 3-O-glycosides. After pollination the transgenic plants showed slower pollen tube growth and fewer developed seeds. Exogenous application of different flavonoid compounds suggested that kaempferol 3-O-glycosides, especially kaempferol 3-O-rhamnoside, regulated pollen tube growth and seed set rather than cyanidin or quercetin 3-O-glycosides. It was found that kaempferol 3-O-rhamnoside might regulate pollen tube growth through effects on auxin, the Rho of plants (ROP) GTPases, calcium and the phosphoinositides signaling pathway. With the inhibition of auxin transport, the transcription levels of Heat Shock Proteins (HSPs) and ROP GTPases were downregulated while the levels were not changed or even enhanced when blocking calcium signaling, suggesting that HSPs and ROP GTPases were downstream of auxin signaling, but upstream of calcium signaling. In summary, kaempferol glycoside concentrations in pistils correlated with auxin transport, the transcription of HSPs and ROP GTPases, and calcium signaling in pollen tubes, culminating in changes to pollen tube growth and seed set.

Activation of PsMYB10.2 Transcription Causes Anthocyanin Accumulation in Flesh of the Red-Fleshed Mutant of 'Sanyueli' (Prunus salicina Lindl.).

Plum is one of the most important stone fruits in the world and anthocyanin-rich plums are increasingly popular due to their health-promoting potential. In this study, we investigated the mechanisms of anthocyanin accumulation in the flesh of the red-fleshed mutant of the yellow-fleshed plum 'Sanyueli'. RNA-Seq and qRT-PCR showed that anthocyanin biosynthetic genes and the transcription factor PsMYB10.2 were upregulated in the flesh of the mutant. Functional testing in tobacco leaves indicated that PsMYB10.2 was an anthocyanin pathway activator and can activate the promoter of the anthocyanin biosynthetic genes PsUFGT and PsGST. The role of PsMYB10.2 in anthocyanin accumulation in the flesh of plum was further confirmed by virus-induced gene silencing. These results provide information for further elucidating the underlying mechanisms of anthocyanin accumulation in the flesh of plum and for the breeding of new red-fleshed plum cultivars.

Unraveling a genetic roadmap for improved taste in the domesticated apple.

Although taste is an important aspect of fruit quality, an understanding of its genetic control remains elusive in apple and other fruit crops. In this study, we conducted genomic sequence analysis of 497 Malus accessions and revealed erosion of genetic diversity caused by apple breeding and possible independent domestication events of dessert and cider apples. Signatures of selection for fruit acidity and size, but not for fruit sugar content, were detected during the processes of both domestication and improvement. Furthermore, we found that single mutations in major genes affecting fruit taste, including Ma1, MdTDT, and MdSOT2, dramatically decrease malate, citrate, and sorbitol accumulation, respectively, and correspond to important domestication events. Interestingly, Ma1 was identified to have pleiotropic effects on both organic acid content and sugar:acid ratio, suggesting that it plays a vital role in determining fruit taste. Fruit taste is unlikely to have been negatively affected by linkage drag associated with selection for larger fruit that resulted from the pyramiding of multiple genes with minor effects on fruit size. Collectively, our study provides new insights into the genetic basis of fruit quality and its evolutionary roadmap during apple domestication, pinpointing several candidate genes for genetic manipulation of fruit taste in apple.

Differential regulation of triterpene biosynthesis induced by an early failure in cuticle formation in apple.

Waxy apple cuticles predominantly accumulate ursane-type triterpenes, but the profile shifts with the induction of skin russeting towards lupane-type triterpenes. We previously characterised several key enzymes in the ursane-type and lupane-type triterpene pathways, but this switch in triterpene metabolism associated with loss of cuticle integrity is not fully understood. To analyse the relationship between triterpene biosynthesis and russeting, we used microscopy, RNA-sequencing and metabolite profiling during apple fruit development. We compared the skin of three genetically-close clones of 'Golden Delicious' (with waxy, partially russeted and fully russeted skin). We identified a unique molecular profile for the russet clone, including low transcript abundance of multiple cuticle-specific metabolic pathways in the early stages of fruit development. Using correlation analyses between gene transcription and metabolite concentration we found MYB transcription factors strongly associated with lupane-type triterpene biosynthesis. We showed how their transcription changed with the onset of cuticle cracking followed by russeting and that one factor, MYB66, was able to bind the promoter of the oxidosqualene cyclase OSC5, to drive the production of lupeol derivatives. These results provide insights into the breakdown of cuticle integrity leading to russet and how this drives MYB-regulated changes to triterpene biosynthesis.

The PyPIF5-PymiR156a-PySPL9-PyMYB114/MYB10 module regulates light-induced anthocyanin biosynthesis in red pear.

Some cultivars of pear (Pyrus L.) show attractive red fruit skin due to anthocyanin accumulation. This pigmentation can be affected by environmental conditions, especially light. To explore the light-induced regulation network for anthocyanin biosynthesis and fruit coloration in pear, small RNA libraries and mRNA libraries from fruit skins of 'Yunhongyihao' pear were constructed to compare the difference between bagging and debagging treatments. Analysis of RNA-seq of fruit skins with limited light (bagged) and exposed to light (debagged), showed that PyPIF5 was down-regulated after bag removal. PymiR156a was also differentially expressed between bagged and debagged fruit skins. We found that PyPIF5 negatively regulated PymiR156a expression in bagged fruits by directly binding to the G-box motif in its promoter. In addition, PymiR156a overexpression promoted anthocyanin accumulation in both pear skin and apple calli. We confirmed that PymiR156a mediated the cleavage of PySPL9, and that the target PySPL9 protein could form heterodimers with two key anthocyanin regulators (PyMYB114/PyMYB10). We proposed a new module of PyPIF5-PymiR156a-PySPL9-PyMYB114/MYB10. When the bagged fruits were re-exposed to light, PyPIF5 was down-regulated and its inhibitory effect on PymiR156a was weakened, which leads to degradation of the target PySPL, thus eliminating the blocking effect of PySPL on the formation of the regulatory MYB complexes. Ultimately, this promotes anthocyanin biosynthesis in pear skin.

Genomic survey and gene expression analysis of the MYB-related transcription factor superfamily in potato (Solanum tuberosum L.).

The MYB transcription factors (TFs) comprise a major TF family in the plant kingdom. Studies increasingly show that MYB-related genes drive physiological functions in plants. However, little is known regarding their regulatory networks and downstream pathways in potato. We conducted a genome-wide analysis of MYB TFs and related proteins in potato (Solanum tuberosum, abbreviated as St), and identified 138 StMYB-related TFs that were phylogenetically classified into three distinct subgroups based on highly conserved gene structures, consensus motifs and protein domain architecture. Segmental duplication events were detected in the StMYB-related gene family by collinearity analysis, which likely contributed to the expansion of this family. Synteny analysis indicated that 41 StMYB-related genes were orthologous to Arabidopsis and 24 to wheat. In addition, RNA-seq analysis identified several tissue-specific and abiotic stress-responsive StMYB-related genes. To determine a potential role of these genes in anthocyanin biosynthesis and drought response, we analyzed the transcriptomes of the white, pigmented, drought-sensitive ('Atlantic') and drought-resistant ('Qingshu No.9') tetraploid potato cultivars from three flowering stages: early, peak (full blooms) and late (foliage falling). The interaction networks of StMYB-related proteins that were differentially expressed between pigmented versus white, as well as the drought-tolerant versus sensitive cultivars were also predicted. Our findings lay the foundation for prospective functional studies of potato StMYB-related TFs.