MYB transcription factor isolated from Raphanus sativus enhances anthocyanin accumulation in chrysanthemum cultivars

Towards the Improvement of Ornamental Attributes in Chrysanthemum: Recent Progress in Biotechnological Advances

Incessant development and introduction of novel cultivars with improved floral attributes are vital in the dynamic ornamental industry. Chrysanthemum (Chrysanthemum morifolium) is a highly favored ornamental plant, ranking second globally in the cut flower trade, after rose. Development of new chrysanthemum cultivars with improved and innovative modifications in ornamental attributes, including floral color, shape, plant architecture, flowering time, enhanced shelf life, and biotic and abiotic stress tolerance, is a major goal in chrysanthemum breeding. Despite being an economically important ornamental plant, the application of conventional and molecular breeding approaches to various key traits of chrysanthemum is hindered owing to its genomic complexity, heterozygosity, and limited gene pool availability. Although classical breeding of chrysanthemum has resulted in the development of several hundreds of cultivars with various morphological variations, the genetic and transcriptional control of various important ornamental traits remains unclear. The coveted blue colored flowers of chrysanthemums cannot be achieved through conventional breeding and mutation breeding due to technical limitations. However, blue-hued flower has been developed by genetic engineering, and transgenic molecular breeding has been successfully employed, leading to substantial progress in improving various traits. The recent availability of whole-genome sequences of chrysanthemum offers a platform to extensively employ MAS to identify a large number of markers for QTL mapping, and GWAS to dissect the genetic control of complex traits. The combination of NGS, multi-omic platforms, and genome editing technologies has provided a tremendous scope to decipher the molecular and regulatory mechanisms. However, the application and integration of these technologies remain inadequate for chrysanthemum. This review, therefore, details the significance of floral attributes, describes the efforts of recent advancements, and highlights the possibilities for future application towards the improvement of crucial ornamental traits in the globally popular chrysanthemum plant.

Anthocyanins in Floral Colors: Biosynthesis and Regulation in Chrysanthemum Flowers

Chrysanthemum (Chrysanthemum morifolium) is an economically important ornamental crop across the globe. As floral color is the major factor determining customer selection, manipulation of floral color has been a major objective for breeders. Anthocyanins are one of the main pigments contributing to a broad variety of colors in the ray florets of chrysanthemum. Manipulating petal pigments has resulted in the development of a vast range of floral colors. Although the candidate genes involved in anthocyanin biosynthesis have been well studied, the genetic and transcriptional control of floral color remains unclear. Despite advances in multi-omics technology, these methods remain in their infancy in chrysanthemum, owing to its large complex genome and hexaploidy. Hence, there is a need to further elucidate and better understand the genetic and molecular regulatory mechanisms in chrysanthemum, which can provide a basis for future advances in breeding for novel and diverse floral colors in this commercially beneficial crop. Therefore, this review describes the significance of anthocyanins in chrysanthemum flowers, and the mechanism of anthocyanin biosynthesis under genetic and environmental factors, providing insight into the development of novel colored ray florets. Genetic and molecular regulatory mechanisms that control anthocyanin biosynthesis and the various breeding efforts to modify floral color in chrysanthemum are detailed.

Transcriptional activation of anthocyanin structural genes in Torenia 'Kauai Rose' via overexpression of anthocyanin regulatory transcription factors

This study was conducted to examine the role of the transcription factors (TFs), RsMYB1 and mPAP1 together with B-Peru (mPAP1 + B-Peru), in regulating anthocyanin biosynthesis in the ornamental torenia (Torenia fournieri) cultivar Kauai Rose using Agrobacterium-mediated transformation. Expression levels of RsMYB1 were the highest in the lines RS5 and RS3, followed by RS4, RS2, and RS1, while transcript levels of mPAP1 + B-Peru increased in the order of PB-6 > PB-5 > PB-7 > PB-8 > PB-2. Moreover, transcript levels of the anthocyanin structural genes in transgenic lines were significantly higher than those in wild-type (WT) plants. Anthocyanin structural gene expression was specifically altered by TF overexpression: the highest expression of anthocyanidin synthase (ANS) was observed in transgenic lines with RsMYB1, while expression of dihydroflavonol-4-reductase (DFR) was the highest in lines with mPAP1 + B-Peru. We expect that enhanced expression of these anthocyanin structural genes will improve anthocyanin content in the flowers of transgenic torenia. Moreover, these results indicate that RsMYB1 and mPAP1 + B-Peru can be exploited as anthocyanin regulatory TFs to enhance anthocyanin content in other horticultural plants.

Roles of R2R3-MYB transcription factors in transcriptional regulation of anthocyanin biosynthesis in horticultural plants

This review contains functional roles of MYB transcription factors in the transcriptional regulation of anthocyanin biosynthesis in horticultural plants. This review describes potential uses of MYB TFs as tools for metabolic engineering for anthocyanin production. Anthocyanins (ranging from red to blue) are controlled by specific branches of the anthocyanin biosynthetic pathway and are mostly visible in ornamentals, fruits, and vegetables. In the present review, we describe which R2R3-MYB transcription factors (TFs) control the transcriptional regulation of anthocyanin structural genes involved in the specific branches of the anthocyanin biosynthetic pathway in various horticultural plants (e.g., ornamentals, fruits, and vegetables). In addition, some MYBs responsible for anthocyanin accumulation in specific tissues are described. Moreover, we highlight the phylogenetic relationships of the MYBs that suppress or promote anthocyanin synthesis in horticultural crops. Enhancement of anthocyanin synthesis via metabolic genetic engineering of anthocyanin MYBs, which is described in the review, is indicative of the potential use of the mentioned anthocyanin-related MYBs as tools for anthocyanin production. Therefore, the MYBs would be suitable for metabolic genetic engineering for improvement of flower colors, fruit quality, and vegetable nutrients.