Chinese researchers have identified a new gene which regulates the ripening of tomatoes. Several genes known to control tomato ripening are members of the NAC family of regulators. To identify others, a team led by Daqi Fu of China Agricultural University blocked the expression of candidate NAC genes. The discovered that silencing NOR-like1 repressed ripening, leaving the tomatoes partially green. The team also engineered plants with defective copies of NOR-like1 and found that this delayed ripening and eventually resulted in partially ripe fruit and impaired seed development. RNA sequencing of these lines revealed that NOR-like1 directly regulates genes involved in ethylene synthesis, carotenoid accumluation, chlorophyll metabolism, and cell wall breakdown. These findings clearly demonstrate a key role for NOR-like1 as a positive regulator of tomato ripening and a potential tool for controlling this important process.
This collection reviews how transcription factors regulate multiple biochemical pathways that underpin fruit ripening traits, including the levels of sugars, acids, pigments, and flavor and aroma compounds and fruit firmness and texture.
Genetic analysis suggests an explanation for differing arrangements of tendrils on grapevine plants, with implications for grape production. Grapevines are unique in that their tendrils, which are usually modified leaves, are also the starting point for the bunches of flowers that will later become fruits. Thus, an understanding of how tendril development is controlled may provide insights into grape production. An international team led by Gan-Yuan Zhong of the USDA-Agricultural Research Service, Geneva, USA, studied a population of grape plants, some of which displayed a normal grapevine tendril arrangment relative to the leaves, and some of which showed alternative arrangements. By comparing the genes that differed in activity between the two types of grapevine, they identified key components in the genetic control of this complex trait.
Combination of iTRAQ proteomics and RNA-seq transcriptomics reveals multiple levels of regulation in phytoplasma-infected Ziziphus jujuba Mill
A multi-omics approach sheds light on the mechanisms of infection and defense at play between jujube trees and an enigmatic pathogen. Phytoplasmas are unculturable bacterial parasites discovered only a few decades ago, which cause deformed growths known as ‘witch's brooms’ in woody plants. A team at Henan Agricultural University, led by Jiancan Feng, explored the mechanisms of phytoplasma infection in the jujube tree (Ziziphus jujuba), by grafting healthy trees with infected branches. They employed a multi-pronged approach, analyzing the trees' gene activity, protein production, and hormone levels following infection. Their results suggest that the plant hormones auxin and jasmonic acid play important early roles in response to phytoplasma infection and that, as the witch's broom developed, processes such as photosynthesis were negatively impacted. These findings underpin future research towards preventing this devastating disease.
The genetic processes that determine the colors in purple kiwifruit have been revealed by researchers in New Zealand. Anthocyanin pigments are not only essential for plant growth and development, but also provide color to make fruit attractive to pollinators and indicate ripeness for the food industry. Andrew Allan and co-workers at the University of Auckland and The New Zealand Institute for Plant and Food Research Limited examined several different kiwifruit species, and found that their color was determined by the ratio of red cyanidin-based to blue delphinidin-based anthocyanins. The team identified four biosynthetic genes that are crucial for accumulating anthocyanins, and showed that two of those genes control the red-to-blue pigment ratio. This new understanding of the anthocyanin profile could allow metabolic engineering of novel fruit colors, possibly with greater health benefits for humans.
Diversity and redundancy of the ripening regulatory networks revealed by the fruitENCODE and the new CRISPR/Cas9 CNR and NOR mutants
The regulatory circuits that govern the expression of genes required for ripening in tomato plants are highly redundant. Fleshy fruits that use the hormone ethylene to regulate ripening have developed independently multiple times in the history of the angiosperms. Guiqin Qu at China Agricultural University in Beijing and colleagues working on the fruitENCODE project are exploring the genetic and epigenetic basis of this convergent evolution. In tomatoes, three transcription factors have been shown to control ethylene production and regulate ripening. However, when gene editing techniques were used to introduce mutations that interfere with the function of these transcription factors, partial ripening or a delay in ripening was observed. The fact that ripening was not abolished indicates that the ripening process is more robust and complex than previously thought.
Integrated analysis of high-throughput sequencing data shows abscisic acid-responsive genes and miRNAs in strawberry receptacle fruit ripening
Researchers in China have uncovered the genetic factors through which the plant hormone ABA controls strawberry ripening. Zisheng Luo’s team at Zhejiang University used high-throughput sequencing to compare gene expression in strawberry plants after they were treated with ABA or an ABA-blocker. They discovered that ABA changes the expression of genes related to other hormones, metabolite synthesis, and breaking down cell walls. The team also checked the expression of short RNA molecules which regulate gene expression, known as microRNAs (miRNAs). They found 26 miRNAs which changed expression in response to ABA, six of which were novel, and identified 18 genes regulated by these miRNAs, including a cell wall gene which may be involved in fruit enlargement. These findings clarify the molecular mechanisms linking ABA with strawberry ripening and lay the groundwork for detailed functional studies.
Investigation of benzylisoquinoline alkaloid biosynthetic pathway and its transcriptional regulation in lotus
Researchers at the Chinese Academy of Sciences have discovered the genes in lotus responsible for the synthesis of benzylisoquinole alkaloids (BIAs), a diverse set of pharmacologically significant plant metabolites. By comparing gene expression in two lotus varieties, a high- and low-BIA cultivar, they identified the genes that were active during BIA biosynthesis as well as five transcription factors which regulate the process. One of the biosynthesis genes is expressed more strongly in the embryo and another in the leaves, leading to the accumulation of different types of BIAs in these tissues. Although many of these genes are related to known BIA synthesis genes in other species, identifying the lotus equivalents not only reveals the particulars of the process in this species but also expands our understanding of BIA synthesis in general.
PpERF3 positively regulates ABA biosynthesis by activating PpNCED2/3 transcription during fruit ripening in peach
Two hormones that regulate fruit ripening are more closely linked than previously thought, according to a study of ripening in peaches. Ethylene is a key ripening hormone in many fruits, and high ethylene levels turn on ethylene response factors (ERFs), genes that trigger production of sugars, pigments, and flavor compounds associated with ripening. Another hormone, abscisic acid (ABA), has recently been found to affect ripening, but its interaction with ethylene is unclear. Zhiqiang Wang and Guohuai Li at the Chinese Academy of Agricultural Sciences and coworkers investigated how ethylene and ABA interact during ripening. They found that as ethylene levels increased, ABA production was stimulated. Further investigation showed that ethylene directly triggered the ABA increase via ERFs. These results illuminate the fruit ripening process, and may help in finding ways to prolong fruit shelf life.
SlMYB75, an MYB-type transcription factor, promotes anthocyanin accumulation and enhances volatile aroma production in tomato fruits
A single gene has been identified in tomatoes that regulates multiple aspects of fruit quality, including levels of health-promoting anthocyanins, opening the door to engineering more nutritious and better-tasting tomatoes. Fruit breeders have long-manipulated genes to enhance traits like yield or disease resistance, but it is rare to find a single gene that can improve multiple aspects of fruit quality. In this study, Zhengguo Li at Chongquing University in China and colleagues show that over-expressing a transcription factor called SIMYB75 results in striking deep purple tomatoes enriched in anthrocyanins–antioxidants thought to be protective against various diseases - which tomatoes are usually devoid of. They also had higher levels of other health-promoting phytochemicals and enhanced production of aroma volatiles, which can influence the taste and flavor of fruit.
The bZIP transcription factor MdHY5 regulates anthocyanin accumulation and nitrate assimilation in apple
The regulatory gene HY5 plays an important role in two biochemical pathways controlling fruit quality and coloration in apple. The gene HY5 has long been recognized as a key regulator of other genes, controlling multiple processes in plant growth and development. A team from Shandong Agricultural University, China, led by Xiao-Fei Wang and Yu-Jin Hao, investigated the gene‘s action in apples, one of the world‘s most important fruit crops. They found that HY5 strongly influences the production of pigments known as anthocyanins, which help give apples their appealing color. They also found evidence that it is involved in regulating nitrogen uptake, a crucial process for plant growth, and that its action is light-activated. These results may prove useful to breeders engineering better quality and more attractive apples for the consumer market.
The tomato HIGH PIGMENT1/DAMAGED DNA BINDING PROTEIN 1 gene contributes to regulation of fruit ripening
A mutation in the tomato gene encoding UV-damaged DNA binding protein 1 (DDB1) delays fruit ripening and softening. Previous studies have established that DDB1 mutants produce fruit with high levels of carotenoids, flavonoids, and vitamin C. However, little was known about the effects of the mutation on fruit ripening processes. Yongsheng Liu at Hefei University of Technology, China, and colleagues showed that DDB1 is implicated in the synthesis of the fruit ripening hormone ethylene, the expression of ripening-associated genes, particularly during early fruit development, and cell wall-related genes. The slower ripening and increased firmness of DDB1 mutant tomatoes highlight this gene as a useful target for improving both the shelf-life and nutritional value of fleshy fruits.
The WRKY transcription factor HpWRKY44 regulates CytP450-like1 expression in red pitaya fruit (Hylocereus polyrhizus)
Two newly characterized genes play important roles in producing antioxidant pigments in red pitaya (dragonfruit). The striking red and yellow pigments known as betalains have antioxidant properties, and are only found in plants of the order Caryophyllales (carnations, beets and cacti). A team from South China Agricultural University led by Yong-hua Qin and Jian-ye Chen studied the genetic control of betalain production in the dragonfruit ( Hylocereus polyrhizus). They found evidence that the gene CytP450-like, which encodes a key enzyme in betalain synthesis, is controlled by a second gene, HpWRKY44. Both genes are highly active during fruit coloration, and HpWRKY44 was shown to bind to and activate a DNA ‘promoter’ of CytP450-like. The results provide key targets for further study of the genetic basis of betalain production.
Transcriptome driven characterization of curly- and smooth-leafed endives reveals molecular differences in the sesquiterpenoid pathway
Genetic analyses show molecular differences that could explain why curly endives taste bitterer than smooth ones. Donato Giannino of the Institute of Agricultural Biology and Biotechnology and colleagues in Italy analyzed the genetic differences between curly and smooth endives, a leafy vegetable used in salads. They found more than 3000 single sequence variations in genes distinguishing the two types from each other. Twenty six genes were involved in the biosynthesis of sesquiterpenoids, metabolites important for plant survival that also contribute to the bitter taste of endives and have antimalarial, sedative and analgesic effects when isolated for humans. Their levels were higher in curly than in smooth endives, potentially contributing to their more bitter taste. The information expands the genetic data available on endives for breeding programs.