Background

The control of plant anthocyanin accumulation is via transcriptional regulation of the genes encoding the biosynthetic enzymes. A key activator appears to be an R2R3 MYB transcription factor. In apple fruit, skin anthocyanin levels are controlled by a gene called MYBA or MYB1, while the gene determining fruit flesh and foliage anthocyanin has been termed MYB10. In order to further understand tissue-specific anthocyanin regulation we have isolated orthologous MYB genes from all the commercially important rosaceous species.

Results

We use gene specific primers to show that the three MYB activators of apple anthocyanin (MYB10/MYB1/MYBA) are likely alleles of each other. MYB transcription factors, with high sequence identity to the apple gene were isolated from across the rosaceous family (e.g. apples, pears, plums, cherries, peaches, raspberries, rose, strawberry). Key identifying amino acid residues were found in both the DNA-binding and C-terminal domains of these MYBs. The expression of these MYB10 genes correlates with fruit and flower anthocyanin levels. Their function was tested in tobacco and strawberry. In tobacco, these MYBs were shown to induce the anthocyanin pathway when co-expressed with bHLHs, while over-expression of strawberry and apple genes in the crop of origin elevates anthocyanins.

Conclusions

This family-wide study of rosaceous R2R3 MYBs provides insight into the evolution of this plant trait. It has implications for the development of new coloured fruit and flowers, as well as aiding the understanding of temporal-spatial colour change.

An R2R3 MYB transcription factor associated with regulation of the anthocyanin biosynthetic pathway in Rosaceae

Flavonoids are a signature class of secondary metabolites formed from a relatively simple collection of scaffolds. They are extensively decorated by chemical reactions including glycosylation, methylation, and acylation. They are present in a wide variety of fruits and vegetables and as such in Western populations it is estimated that 20-50 mg of flavonoids are consumed daily per person. In planta they have demonstrated to contribute to both flower color and UV protection. Their consumption has been suggested to presenta wide range of health benefits. Recent technical advances allowing affordable whole genome sequencing, as well as a better inventory of species-by-species chemical diversity, have greatly advanced our understanding as to how flavonoid biosynthesis pathways vary across species. In parallel, reverse genetics combined with detailed molecular phenotyping is currently allowing us to elucidate the functional importance of individual genes and metabolites and by this means to provide further mechanistic insight into their biological roles. Here we provide an inventory of current knowledge of pathways of flavonoid biosynthesis in both the model plant Arabidopsis thaliana and a range of crop species, including tomato, maize, rice, and bean.

Current understanding of the pathways of flavonoid biosynthesis in model and crop plants

Predicting physical response of an artificially structured material is of particular interest for scientific and engineering applications. Here we use deep learning to predict optical response of artificially engineered nanophotonic devices. In addition to predicting forward approximation of transmission response for any given topology, this approach allows us to inversely approximate designs for a targeted optical response. Our Deep Neural Network (DNN) could design compact (2.6 × 2.6 μm2) silicon-on-insulator (SOI)-based 1 × 2 power splitters with various target splitting ratios in a fraction of a second. This model is trained to minimize the reflection (to smaller than ~ −20 dB) while achieving maximum transmission efficiency above 90% and target splitting specifications. This approach paves the way for rapid design of integrated photonic components relying on complex nanostructures.

Deep Neural Network Inverse Design of Integrated Photonic Power Splitters.

Genetics and Control of Tomato Fruit_Ripening and Quality Attributes

Abiotic and biotic stresses adversely affect the growth and productivity of plants and constitute the major yield-limiting factor in agriculture. In recent years, several  transcription factors (TF) have been identified that can function as switches to control the expression of potential stress-related genes. These transcription factors play crucial roles in governing transcriptional reprogramming during development in plant biological systems and are also capable of increasing the tolerance of plants to abiotic and biotic stresses. Thus, identifying and characterizing critical genes that are involved in plant stress responses are essential for the development of transgenic plants that exhibit enhanced stress tolerance. This review describes the DREB/ERF, MYB, NAC and WRKY TF and summarizes the studies that highlight their potential in engineering abiotic and biotic stress tolerance in transgenic plants.

Potential use of the DREB/ERF, MYB, NAC and WRKY transcription factors to improve abiotic and biotic stress in transgenic plants

MADS-domain proteins are important transcription factors involved in many biological processes of plants. In our study, a tomato MADS-box gene, SlFYFL, was isolated. SlFYFL is expressed in all tissues of tomato and significantly higher in mature leave, fruit of different stages, AZ (abscission zone) and sepal. Delayed leaf senescence and fruit ripening, increased storability and longer sepals were observed in 35S:FYFL tomato. The accumulation of carotenoid was reduced, and ethylene content, ethylene biosynthetic and responsive genes were down-regulated in 35S:FYFL fruits. Abscission zone (AZ) did not form normally and abscission zone development related genes were declined in AZs of 35S:FYFL plants. Yeast two-hybrid assay revealed that SlFYFL protein could interact with SlMADS-RIN, SlMADS1 and SlJOINTLESS, respectively. These results suggest that overexpression of SlFYFL regulate fruit ripening and development of AZ via interactions with the ripening and abscission zone-related MADS box proteins.

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Overexpression of a novel MADS-box gene SlFYFL delays senescence, fruit ripening and abscission in tomato

The basic helix-loop-helix (bHLH) proteins are a large family of transcription factors that control various developmental processes in eukaryotes, but the biological roles of most bHLH proteins are not very clear, especially in tomato. In this study, a PRE-like atypical bHLH gene was isolated and designated as SlPRE2 in tomato. SlPRE2 was highly expressed in immature-green fruits, moderately in young leaves, flowers, and mature-green fruits. To further research the function of SlPRE2, a 35 S:PRE2 binary vector was constructed and transformed into wild type tomato. The transgenic plants showed increased leaf angle and stem internode length, rolling leaves with decreased chlorophyll content. The water loss rate of detached leaves was increased in young transgenic lines but depressed in mature leaves. Besides, overexpression of SlPRE2 promoted morphogenesis in seedling development, producing light-green unripening fruits and yellowing ripen fruits with reduced chlorophyll and carotenoid accumulation in pericarps, respectively. Quantitative RT-PCR analysis showed that expression of the chlorophyll related genes, such as GOLDEN 2-LIKE and RbcS, were decreased in unripening 35 
 S:PRE2 fruit, and carotenoid biosynthesis-related genes PHYTOENE SYNTHASE1A and ζ-CAROTENE DESATURASE in ripening fruit were also down-regulated. These results suggest that SlPRE2 affects plant morphology and is a negative regulator of fruit pigment accumulation.

Overexpression of SlPRE2, an atypical bHLH transcription factor, affects plant morphology and fruit pigment accumulation in tomato.

Kohlrabi (Brassica oleracea var. gongylodes L.) is an important dietary vegetable cultivated and consumed widely for the round swollen stem. Purple kohlrabi shows abundant anthocyanin accumulation in the leaf and swollen stem. Here, different kinds of anthocyanins were separated and identified from the purple kohlrabi cultivar (Kolibri) by high-performance liquid chromatography-electrospray ionization tandem mass spectrometry. In order to study the molecular mechanism of anthocyanin biosynthesis in purple kohlrabi, the expression of anthocyanin biosynthetic genes and regulatory genes in purple kohlrabi and a green cultivar (Winner) was examined by quantitative PCR. In comparison with the colorless parts in the two cultivars, most of the anthocyanin biosynthetic genes and two transcription factors were drastically upregulated in the purple tissues. To study the effects of light shed on the anthocyanin accumulation of kohlrabi, total anthocyanin contents and transcripts of associated genes were analyzed in sprouts of both cultivars grown under light and dark conditions.

Anthocyanin Accumulation and Molecular Analysis of Correlated Genes in Purple Kohlrabi (Brassica oleracea var. gongylodes L.).

Adverse environmental conditions, such as drought, high salinity and extreme temperature, severely affect the growth and productivity of crop plants MADS-box transcription factors have been described to participate in stress responses In our study, a MADS-box transcription factor gene, SlMBP8, has been cloned from tomato The expression of SlMBP8 was induced by Methyl-jasmonic acid (MeJA), high salinity, high temperature, wounding and dehydration Whereas, the transcript of SlMBP8 was down-regulated by Abscisic acid (ABA), 1-aminocyclopropane-1-carboxylic acid (ACC) and Indole-3-acetic acid (IAA) To further elucidate the function of SlMBP8 gene in response to abiotic stress, plants by knockdown of SlMBP8 through RNA interference (RNAi) were used for investigating the effect of drought and salt stresses on tomato seedlings of wild type (WT) and SlMBP8-RNAi lines Seedling growth of SlMBP8-RNAi plants was less inhibited by salt than WT at post-germination stage Transgenic plants became more tolerant to drought and salt stress than WT plants in soil, which was demonstrated by higher levels of chlorophyll and water contents, lower water loss rate and malondialdehyde (MDA) contents In addition, the expression of multiple stresses related genes were significantly up-regulated in the RNAi lines under control and abiotic stresses Taken together, these results suggest that SlMBP8 function as a negative stress-responsive transcription factor in the drought and high salinity stress signaling pathways, and may have promising applications in the engineering of drought- and salt-tolerant tomato

Tomato (Solanum lycopersicum) MADS-box transcription factor SlMBP8 regulates drought, salt tolerance and stress-related genes.

Histone deacetylation is one of the well characterized post-translational modifications related to transcriptional repression in eukaryotes. The process of histone deacetylation is achieved by histone deacetylases (HDACs). Over the last decade, substantial advances in our understanding of the mechanism of fruit ripening have been achieved, but the role of HDACs in this process has not been elucidated. In our study, an RNA interference (RNAi) expression vector targeting SlHDA1 was constructed and transformed into tomato plants. Shorter fruit ripening time and decreased storability were observed in SlHDA1 RNAi lines. The accumulation of carotenoid was increased through an alteration of the carotenoid pathway flux. Ethylene content, ethylene biosynthesis genes (ACS2, ACS4 and ACO1, ACO3) and ripening-associated genes (RIN, E4, E8, Cnr, TAGL1, PG, Pti4 and LOXB) were significantly up-regulated in SlHDA1 RNAi lines. In addition, the expression of fruit cell wall metabolism genes (HEX, MAN, TBG4, XTH5 and XYL) was enhanced compared with wild type. Furthermore, SlHDA1 RNAi seedlings displayed shorter hypocotyls and were more sensitive to ACC (1-aminocyclopropane-1-carboxylate) than the wild type. The results of our study indicate that SlHDA1 functions as a negative regulator of fruit ripening by affecting ethylene synthesis and carotenoid accumulation.

Zhiguo Zhu

Papers

Overexpression of a novel MADS-box gene SlFYFL delays senescence, fruit ripening and abscission in tomato

Overexpression of SlPRE2, an atypical bHLH transcription factor, affects plant morphology and fruit pigment accumulation in tomato.

Anthocyanin Accumulation and Molecular Analysis of Correlated Genes in Purple Kohlrabi (Brassica oleracea var. gongylodes L.).

Tomato (Solanum lycopersicum) MADS-box transcription factor SlMBP8 regulates drought, salt tolerance and stress-related genes.

The tomato histone deacetylase SlHDA1 contributes to the repression of fruit ripening and carotenoid accumulation.