Manipulation of the blue light photoreceptor cryptochrome 2 in tomato affects vegetative development, flowering time, and fruit antioxidant content

Association of the circadian rhythmic expression of GmCRY1a with a latitudinal cline in photoperiodic flowering of soybean

Photoperiodic control of flowering time is believed to affect latitudinal distribution of plants. The blue light receptor CRY2 regulates photoperiodic flowering in the experimental model plant Arabidopsis thaliana. However, it is unclear whether genetic variations affecting cryptochrome activity or expression is broadly associated with latitudinal distribution of plants. We report here an investigation of the function and expression of two cryptochromes in soybean, GmCRY1a and GmCRY2a. Soybean is a short-day (SD) crop commonly cultivated according to the photoperiodic sensitivity of cultivars. Both cultivated soybean (Glycine max) and its wild relative (G. soja) exhibit a strong latitudinal cline in photoperiodic flowering. Similar to their Arabidopsis counterparts, both GmCRY1a and GmCRY2a affected blue light inhibition of cell elongation, but only GmCRY2a underwent blue light- and 26S proteasome-dependent degradation. However, in contrast to Arabidopsis cryptochromes, soybean GmCRY1a, but not GmCRY2a, exhibited a strong activity promoting floral initiation, and the level of protein expression of GmCRY1a, but not GmCRY2a, oscillated with a circadian rhythm that has different phase characteristics in different photoperiods. Consistent with the hypothesis that GmCRY1a is a major regulator of photoperiodic flowering in soybean, the photoperiod-dependent circadian rhythmic expression of the GmCRY1a protein correlates with photoperiodic flowering and latitudinal distribution of soybean cultivars. We propose that genes affecting protein expression of the GmCRY1a protein play an important role in determining latitudinal distribution of soybeans.

Genetic engineering of carotenoid formation in tomato fruit and the potential application of systems and synthetic biology approaches

The health benefits conferred by numerous carotenoids have led to attempts to elevate their levels in foodstuffs. Tomato fruit and its products contain the potent antioxidant lycopene and are the predominant source of lycopene in the human diet. In addition, tomato products are an important source of provitamin A (beta-carotene). The presence of other health promoting phytochemicals such as tocopherols and flavonoids in tomato has led to tomato and its products being termed a functional food. Over the past decade genetic/metabolic engineering of carotenoid biosynthesis and accumulation has resulted in the generation of transgenic varieties containing high lycopene and beta-carotene contents. In achieving this important goal many fundamental lessons have been learnt. Most notably is the observation that the endogenous carotenoid pathways in higher plants appear to resist engineered changes. Typically, this resistance manifests itself through intrinsic regulatory mechanisms that are "silent" until manipulation of the pathway is initiated. These mechanisms may include feedback inhibition, forward feed, metabolite channelling, and counteractive metabolic and cellular perturbations. In the present article we will review progress made in the genetic engineering of carotenoids in tomato fruit, highlighting the limiting regulatory mechanisms that have been observed experimentally. The predictability and efficiency of the present engineering strategies will be questioned and the potential of more Systems and Synthetic Biology approaches to the enhancement of carotenoids will be assessed.

Virus-induced gene silencing and its application in characterizing genes involved in water-deficit-stress tolerance

Understanding post-transcriptional gene silencing (PTGS) phenomena in plants has provided breakthroughs in advancing plant functional genomics. A recently developed approach based on one of the strategies adopted by plants to defend against viruses, called virus-induced gene silencing (VIGS), is being widely used to enumerate the function of plant genes. Since its discovery, VIGS has been widely used to characterize plant genes involved in metabolic pathways, homeostasis, basic cellular functions, plant-microbe, plant-nematode and plant-herbivore interaction. Recently, the application of this technique has been extended to characterize the genes and cellular processes involved in abiotic-stress tolerance, and in particular drought and oxidative stress. Because abiotic-stress tolerance is multigenic, identification and characterization of genes involved in this process is challenging. VIGS could become one among the several potential tools in understanding the relevance of these stress-responsive genes. Development of VIGS protocols for the use of heterologous gene sequences as VIGS-inducers has extended its applicability to analyze genes of VIGS recalcitrant plant species. This article describes the methodology of VIGS for characterizing the water-deficit-stress-responsive genes, precautions to be taken during the experimentation, and future application of this technology as a fast forwarded as well as a reverse genetics tool to identify and characterize plant genes involved in drought tolerance. We also describe the importance of accurate water-deficit-stress imposition and quantification of stress-induced changes in the silenced plants during the process of screening to identify genes responsible for tolerance. Further, limitations of VIGS in characterizing the abiotic-stress-responsive genes are noted, with suggestions to overcome these limitations.

Diurnal and circadian rhythms in the tomato transcriptome and their modulation by cryptochrome photoreceptors

BACKGROUND

Circadian clocks are internal molecular time-keeping mechanisms that provide living organisms with the ability to adjust their growth and physiology and to anticipate diurnal environmental changes. Circadian clocks, without exception, respond to light and, in plants, light is the most potent and best characterized entraining stimulus. The capacity of plants to respond to light is achieved through a number of photo-perceptive proteins including cryptochromes and phytochromes. There is considerable experimental evidence demonstrating the roles of photoreceptors in providing light input to the clock.

METHODOLOGY

In order to identify genes regulated by diurnal and circadian rhythms, and to establish possible functional relations between photoreceptors and the circadian clock in tomato, we monitored the temporal transcription pattern in plants entrained to long-day conditions, either by large scale comparative profiling, or using a focused approach over a number of photosensory and clock-related genes by QRT-PCR. In parallel, focused transcription analyses were performed in cry1a- and in CRY2-OX tomato genotypes.

CONCLUSIONS

We report a large series of transcript oscillations that shed light on the complex network of interactions among tomato photoreceptors and clock-related genes. Alteration of cryptochrome gene expression induced major changes in the rhythmic oscillations of several other gene transcripts. In particular, over-expression of CRY2 had an impact not only on day/night fluctuations but also on rhythmicity under constant light conditions. Evidence was found for widespread diurnal oscillations of transcripts encoding specific enzyme classes (e.g. carotenoid biosynthesis enzymes) as well as for post-transcriptional diurnal and circadian regulation of the CRY2 transcript.

Carotenoid metabolism: biosynthesis, regulation, and beyond

Carotenoids are indispensable to plants and play a critical role in human nutrition and health. Significant progress has been made in our understanding of carotenoid metabolism in plants. The biosynthetic pathway has been extensively studied. Nearly all the genes encoding the biosynthetic enzymes have been isolated and characterized from various organisms. In recent years, there is an increasing body of work on the signaling pathways and plastid development, which might provide global control of carotenoid biosynthesis and accumulation. Herein, we will highlight recent progress on the biosynthesis, regulation, and metabolic engineering of carotenoids in plants, as well as the future research towards elucidating the regulatory mechanisms and metabolic network that control carotenoid metabolism.

SHORT HYPOCOTYL IN WHITE LIGHT1, a serine-arginine-aspartate-rich protein in Arabidopsis, acts as a negative regulator of photomorphogenic growth

Light is an important factor for plant growth and development. We have identified and functionally characterized a regulatory gene SHORT HYPOCOTYL IN WHITE LIGHT1 (SHW1) involved in Arabidopsis (Arabidopsis thaliana) seedling development. SHW1 encodes a unique serine-arginine-aspartate-rich protein, which is constitutively localized in the nucleus of hypocotyl cells. Transgenic analyses have revealed that the expression of SHW1 is developmentally regulated and is closely associated with the photosynthetically active tissues. Genetic and molecular analyses suggest that SHW1 acts as a negative regulator of light-mediated inhibition of hypocotyl elongation, however, plays a positive regulatory role in light-regulated gene expression. The shw1 mutants also display shorter hypocotyl in dark, and analyses of shw1 cop1 double mutants reveal that SHW1 acts nonredundantly with COP1 to control hypocotyl elongation in the darkness. Taken together, this study provides evidences that SHW1 is a regulatory protein that is functionally interrelated to COP1 and plays dual but opposite regulatory roles in photomorphogenesis.

Plant metabolomics and its potential application for human nutrition

With the growing interest in the use of metabolomic technologies for a wide range of biological targets, food applications related to nutrition and quality are rapidly emerging. Metabolomics offers us the opportunity to gain deeper insights into, and have better control of, the fundamental biochemical basis of the things we eat. So doing will help us to design modified breeding programmes aimed at better quality produce; optimised food processing strategies and ultimately, improved (micro)nutrient bioavailability and bioefficacy. A better understanding of the pathways responsible for the biosynthesis of nutritionally relevant metabolites is key to gaining more effective control of the absence/level of presence of such components in our food. Applications of metabolomic technologies in both applied and fundamental science strategies are therefore growing rapidly in popularity. Currently, the world has two highly contrasting nutrition-related problems--over-consumption and under-nourishment. Dramatic increases in the occurrence of overweight individuals and obesity in developed countries are in staggering contrast to the still-familiar images of extreme malnutrition in many parts of the developing world. Both problems require a modified food supply, achieved through highly contrasting routes. For each, metabolomics has a future role to play and this review shall deal with this key dichotomy and illustrate where metabolomics may have a future part to play. In this short overview, attention is given to how the various technologies have already been exploited in a plant-based food context related to key issues such as biofortification, bioprotectants and the general link between food composition and human health. Research on key crops such as rice and tomato are used as illustration of potentially broader application across crop species. Although the focus is clearly on food supply, some attention is given to the complementary field of research, nutrigenomics, where similar technologies are being applied to understand nutrition better from the human side.

Metabolic engineering of carotenoid biosynthesis in plants

Carotenoids are one of the most diverse classes of natural compounds. Plant carotenoids are composed of a C40 isoprenoid skeleton with or without epoxy, hydroxy and keto groups. They have fundamental roles in human nutrition as antioxidants and vitamin A precursors and their consumption is increasingly associated with protection from a range of diseases. They are also used commercially as safe food, feed and cosmetic colorants and they protect plants from photooxidative stress. In the past six years many metabolic engineering efforts have been undertaken in plants aiming to improve the nutritional value of staple crops, to enable the use of plants as 'cell factories' for producing specialty carotenoids and to improve plant resistance to abiotic stress.

Structural and functional genomics of tomato

Tomato (Solanum lycopersicum L.) is the most intensively investigated Solanaceous species both in genetic and genomics studies. It is a diploid species with a haploid set of 12 chromosomes and a small genome (950 Mb). Based on the detailed knowledge on tomato structural genomics, the sequencing of the euchromatic regions started in the year 2005 as a common effort of different countries. The manuscript focuses on markers used for tomato, on mapping efforts mainly based on exploitation of natural biodiversity, and it gives an updated report on the international sequencing activities. The principal tools developed to explore the function of tomato genes are also summarized, including mutagenesis, genetic transformation, and transcriptome analysis. The current progress in bioinformatic strategies available to manage the overwhelming amount of data generated from different tomato "omics" approaches is reported, and emphasis is given to the effort of producing a computational workbench for the analysis of the organization, as well as the functionality and evolution of the Solanaceae family.

Genetic modification of plant metabolism for human health benefits

There has been considerable research progress over the past decade on elucidating biosynthetic pathways for important human health components of crops. This has enabled the use of genetic modification (GM) techniques to develop crop varieties with increased amounts of essential vitamins and minerals, and improved profiles of 'nutraceutical' compounds. Much of the research into vitamins and minerals has focused on generating new varieties of staple crops to improve the diet of populations in developing nations. Of particular note is the development of new rice lines with increased amounts of provitamin A and iron. Research on modifying production of nutraceuticals has generally been aimed at generating new crops for markets in the developed nations, commonly to deliver distinctive cultivars with high consumer appeal. Most progress on nutraceuticals has been made with just a few types of metabolites to date, in particular in the production of novel long-chain polyunsaturated fatty acids in oil-seed crops and to increase amounts of flavonoids and carotenoids in tomato and potato. However, given the rapid progress on elucidating plant metabolite biosynthetic pathways, wide-ranging success with metabolic engineering for levels of human health-related compounds in plants would be expected in the near future. A key aspect for future success will be better medical information to guide metabolic engineering endeavors. Although the desired levels of many vitamins are known, detailed information is lacking for most of the nutraceuticals that have attracted much interest over the past few years.

Cryptochrome signaling in plants

Cryptochromes are blue light receptors that mediate various light-induced responses in plants and animals. They share sequence similarity to photolyases, flavoproteins that catalyze the repair of UV light-damaged DNA, but do not have photolyase activity. Arabidopsis cryptochromes work together with the red/far-red light receptor phytochromes to regulate various light responses, including the regulation of cell elongation and photoperiodic flowering, and are also found to act together with the blue light receptor phototropins to mediate blue light regulation of stomatal opening. The signaling mechanism of Arabidopsis cryptochromes is mediated through negative regulation of COP1 by direct CRY-COP1 interaction through CRY C-terminal domain. Arabidopsis CRY dimerized through its N-terminal domain and dimerization of CRY is required for light activation of the photoreceptor activity. Recently, significant progresses have been made in our understanding of cryptochrome functions in other dicots such as pea and tomato and lower plants including moss and fern. This review will focus on recent advances in functional and mechanism characterization of cryptochromes in plants. It is not intended to cover every aspect of the field; readers are referred to other review articles for historical perspectives and a more comprehensive understanding of this photoreceptor.

Fruit ripening mutants yield insights into ripening control

Fruit ripening is a developmental process that is exclusive to plants whereby mature seed-bearing organs undergo physiological and metabolic changes that promote seed dispersal. Molecular investigations into ripening control mechanisms have been aided by the recent cloning of tomato ripening genes that were previously known only through mutation. Advances in the genomics of tomato have provided genetic and molecular tools that have facilitated the positional and candidate-gene-based cloning of several key ripening genes. These discoveries have created new inroads into understanding of the primary ripening control mechanisms, including transcription factors such as those encoded by the RIPENING-INHIBITOR (RIN) MADS-box and COLOURLESS NON-RIPENING (CNR) SPB-box genes, which are necessary for the progression of virtually all ripening processes. They have also facilitated the elucidation of downstream signal transduction components that impact the hormonal and environmental stimuli that coordinate and modulate ripening phenotypes.

Microclimate influence on mineral and metabolic profiles of grape berries

The grape berry microclimate is known to influence berry quality. The effects of the light exposure of grape berry clusters on the composition of berry tissues were studied on the "Merlot" variety grown in a vineyard in Bordeaux, France. The light exposure of the fruiting zone was modified using different intensities of leaf removal, cluster position relative to azimuth, and berry position in the cluster. Light exposures were identified and classified by in situ measurements of berry temperatures. Berries were sampled at maturity (>19 Brix) for determination of skin and/or pulp chemical and metabolic profiles based on (1) chemical and physicochemical measurement of minerals (N, P, K, Ca, Mg), (2) untargeted 1H NMR metabolic fingerprints, and HPLC targeted analyses of (3) amino acids and (4) phenolics. Each profile defined by partial least-square discriminant analysis allowed us to discriminate berries from different light exposure. Discriminant compounds between shaded and light-exposed berries were quercetin-3-glucoside, kaempferol-3-glucoside, myricetin-3-glucoside, and isorhamnetin-3-glucoside for the phenolics, histidine, valine, GABA, alanine, and arginine for the amino acids, and malate for the organic acids. Capacities of the different profiling techniques to discriminate berries were compared. Although the proportion of explained variance from the 1H NMR fingerprint was lower compared to that of chemical measurements, NMR spectroscopy allowed us to identify lit and shaded berries. Light exposure of berries increased the skin and pulp flavonols, histidine and valine contents, and reduced the organic acids, GABA, and alanine contents. All the targeted and nontargeted analytical data sets used made it possible to discriminate sun-exposed and shaded berries. The skin phenolics pattern was the most discriminating and allowed us to sort sun from shade berries. These metabolite classes can be used to qualify berries collected in an undetermined environment. The physiological significance of light and temperature effects on berry composition is discussed.

CRY-DASHgene expression is under the control of the circadian clock machinery in tomato

Recently a new member of the blue-light photoreceptor family, CRY-DASH, was reported in Arabidopsis, though its distinctive biological functions are still unclear. We characterized the CRY-DASH gene of tomato and evidenced that its mRNA is expressed in both seeds and adult organs showing diurnal and circadian fluctuations. Moreover, the CRY-DASH transcription pattern is altered in both in a cry1a mutant and in a transgenic CRY2 overexpressor suggesting that CRY-DASH regulation must be mediated at least partially by an interaction of CRY1a and CRY2 with the timekeeping mechanism.

Involvement of rice cryptochromes in de-etiolation responses and flowering

In order to elucidate the function of cryptochromes (cry) in rice, we have characterized all rice CRY genes, including OsCRY1a, OsCRY1b and OsCRY2. Our studies revealed that OsCRY1 genes were mainly expressed in the green plant tissue, while OsCRY2 gene expression was high in the coleoptile, flower and callus. Light treatment affected neither the expression of any of the OsCRY genes nor the stability of their transcripts. However, it was found that Oscry2 protein was negatively regulated by blue light. Moreover, the level of Oscry2 protein also decreased upon red light treatment, and this red light-dependent degradation was shown to be mediated by phytochrome B. Overexpression of OsCRY1 genes resulted in an increased responsiveness to blue light when measuring coleoptile growth inhibition. Moreover, growth of leaf sheaths and blades was also repressed more in OsCRY1 overexpressers than in wild type (WT) under blue light conditions. These results suggest that Oscry1s are responsible for regulating blue light-mediated de-etiolation in rice. In addition, OsCRY2 antisense transgenic rice flowered later than WT under both long-day and short-day conditions, indicating that Oscry2 is involved in the promotion of flowering time in rice.

Cryptochrome 2 is involved in betacyanin decomposition induced by blue light in Suaeda salsa

Seeds of the halophyte Suaeda salsa (L.) Pall. were cultured in 24 h dark and 14 h blue light / 10 h dark to examine the role of blue light and the blue-light-absorbing photoreceptor cryptochrome 2 (CRY2) in betacyanin accumulation, hypocotyl elongation and cotyledon opening in S. salsa seedlings. Darkness significantly promoted betacyanin accumulation and hypocotyl elongation but inhibited cotyledon opening. Blue light suppressed betacyanin accumulation and hypocotyl elongation but stimulated cotyledon opening. Betacyanin in S. salsa seedlings decomposed with time in blue light. Western blot analysis showed that CRY2 protein accumulated both in hypocotyls and cotyledons of S. salsa seedlings grown in dark, but degraded with time in blue light, which was paralleled by a decrease of tyrosine hydroxylation activity of tyrosinase, a key enzyme involved in the betalain biosynthesis pathway. These results suggest that CRY2 protein mediates betacyanin decomposition via inactivation of tyrosinase in S. salsa seedlings, and the blue-light-dependent degradation of CRY2 protein is crucial to its function.

Functional and signaling mechanism analysis of rice CRYPTOCHROME 1

Cryptochromes (CRY) are blue-light photoreceptors that mediate various light responses, such as inhibition of hypocotyl elongation, enhancement of cotyledon expansion, anthocyanin accumulation and stomatal opening in Arabidopsis. The signaling mechanism of Arabidopsis CRY is mediated through direct interaction with COP1, a negative regulator of photomorphogenesis. CRY has now been characterized in tomato, pea, moss and fern, but its function in monocots is largely unknown. Here we report the function and basic signaling mechanism of rice cryptochrome 1 (OsCRY1). Overexpresion of OsCRY1b resulted in a blue light-dependent short hypcotyl phenotype in Arabidopsis, and a short coleoptile, leaf sheath and leaf blade phenotype in rice (Oryza sativa). On fusion with beta-glucuronidase (GUS), the C-terminal domain of either OsCRY1a (OsCCT1a) or OsCRY1b (OsCCT1b) mediated a constitutive photomorphogenic (COP) phenotype in both Arabidopsis and rice, whereas OsCCT1b mutants corresponding to missense mutations in previously described Arabidopsis cry1 alleles failed to confer a COP phenotype. Yeast two-hybrid and subcellular co-localization studies demonstrated that OsCRY1b interacted physically with rice COP1 (OsCOP1). From these results, we conclude that OsCRY1 is implicated in blue-light inhibition of coleoptile and leaf elongation during early seedling development in rice, and that the signaling mechanism of OsCRY1 involves direct interaction with OsCOP1.

Cryptochrome 1 from Brassica napus is up-regulated by blue light and controls hypocotyl/stem growth and anthocyanin accumulation

Cryptochromes are blue/ultraviolet-A light sensing photoreceptors involved in regulating various growth and developmental responses in plants. Investigations on the structure and functions of cryptochromes in plants have been largely confined to Arabidopsis (Arabidopsis thaliana), tomato (Lycopersicon esculentum), and pea (Pisum sativum). We report here the characterization of the cryptochrome 1 gene from Brassica napus (BnCRY1), an oilseed crop, and its functional validation in transgenics. The predicted BnCRY1 protein sequence shows a high degree of sequence identity (94%) to Arabidopsis CRY1. A semiquantitative reverse transcription-polymerase chain reaction and the western-blot analysis revealed that blue light up-regulates its transcript and protein levels in young seedlings. The BnCRY1 promoter harbors conventional light-responsive cis-acting elements, which presumably impart light activation to the GUS (beta-glucuronidase) reporter gene expressed in Arabidopsis. Although the BnCRY1 transcript could be detected in all the tissues examined, its protein was virtually undetectable in mature leaves and the root, indicating a tissue-specific translational control or protein turnover. The antisense-BnCRY1 Brassica transgenic seedlings accumulated negligible levels of CRY1 protein and displayed an elongated hypocotyl when grown under continuous white or blue light (but not under red or far-red light); the accumulation of anthocyanins was also reduced significantly. The adult transformants were also found to be tall when grown under natural light environment in a containment facility without any artificial illumination. These data provide functional evidence for a role of blue light up-regulated cry1 in controlling photomorphogenesis in Brassica species.

Understanding carotenoid metabolism as a necessity for genetic engineering of crop plants

As a proof of concept, the qualitative and quantitative engineering of carotenoid formation has been achieved in crop plants. Successful reports in tomato, potato, rice, and canola all describe the enhancement of carotenoid with nutritional value, while in model systems such as tobacco and Arabidopsis the engineering of carotenoid to confer abiotic stress has been described. For all the successful applications there have been many examples of unintended/unpredicted phenotypes and results. Typically this has resided from our lack of understanding of carotenoid formation and its regulation. In the present article, we will review advances in carotenoid formation and its regulation to illustrate how metabolic engineering experiments have shed light on regulatory mechanisms.

The cryptochrome gene family in pea includes two differentially expressed CRY2 genes

The cryptochromes are a family of blue light photoreceptors that play important roles in the control of plant development. We have characterised the cryptochrome gene family in the model legume garden pea (Pisum sativum L.). Pea contains three expressed cryptochrome genes; a single CRY1 orthologue, and two distinct CRY2 genes that we have termed CRY2a and CRY2b. Genomic southern blots indicate that there are unlikely to be more CRY genes in pea. Each of the three genes encodes a full-length CRY protein that contains all the major domains characteristic of other higher plant cryptochromes. Database searches have identified Medicago truncatula expressed sequence tags (ESTs) corresponding to all three genes, whereas only a single CRY2 is represented in EST collections from the more distantly related legumes soybean and Lotus japonicus. The proteins encoded by the pea and Medicago CRY2b genes are distinguished from other CRY2 proteins by their shorter C-terminus. Expression analyses have identified marked differences in the regulation of the three genes, with CRY2b expression in particular distinguished by high-amplitude diurnal cycling and rapid repression in seedlings transferred from darkness to blue light.

Cryptochrome 1 contributes to blue-light sensing in pea

Cryptochromes are widespread in higher plants but their physiological roles as blue-light photoreceptors have been examined in relatively few species. Screening in a phyA null mutant background has identified several blue-light response mutants in pea (Pisum sativum), including one that carries a substitution of a highly conserved glycine residue in the N-terminal photolyase-homologous domain of the pea CRY1 gene. Analyses of cry1, phyA, and phyB mutants show that all three photoreceptors contribute to seedling photomorphogenesis under high-irradiance blue light, whereas phyA is the main photoreceptor active under low irradiances. Triple phyA phyB cry1 mutants grown under high-irradiance blue light are indistinguishable from dark-grown wild-type plants in length and leaf expansion but show a small residual response to higher-irradiance white light. Monogenic cry1 mutants have little discernable phenotype at the seedling stage, but later in development are more elongated than wild-type plants. In addition, the loss of cry1 moderates the short-internode phenotype of older phyA mutants, suggesting an antagonism between phyA and cry1 under some conditions. Pea cry1 has a small inhibitory effect on flowering under long and short days. However, the phyA cry1 double mutant retains a clear promotion of flowering in response to blue-light photoperiod extensions, indicating a role for one or more additional blue-light photoreceptors in the control of flowering in pea.

Biogenesis, molecular regulation and function of plant isoprenoids

Isoprenoids represent the oldest class of known low molecular-mass natural products synthesized by plants. Their biogenesis in plastids, mitochondria and the endoplasmic reticulum-cytosol proceed invariably from the C5 building blocks, isopentenyl diphosphate and/or dimethylallyl diphosphate according to complex and reiterated mechanisms. Compounds derived from the pathway exhibit a diverse spectrum of biological functions. This review centers on advances obtained in the field based on combined use of biochemical, molecular biology and genetic approaches. The function and evolutionary implications of this metabolism are discussed in relation with seminal informations gathered from distantly but related organisms.

Fruit-specific RNAi-mediated suppression of DET1 enhances carotenoid and flavonoid content in tomatoes

Tomatoes are a principal dietary source of carotenoids and flavonoids, both of which are highly beneficial for human health. Overexpression of genes encoding biosynthetic enzymes or transcription factors have resulted in tomatoes with improved carotenoid or flavonoid content, but never with both. We attempted to increase tomato fruit nutritional value by suppressing an endogenous photomorphogenesis regulatory gene, DET1, using fruit-specific promoters combined with RNA interference (RNAi) technology. Molecular analysis indicated that DET1 transcripts were indeed specifically degraded in transgenic fruits. Both carotenoid and flavonoid contents were increased significantly, whereas other parameters of fruit quality were largely unchanged. These results demonstrate that manipulation of a plant regulatory gene can simultaneously influence the production of several phytonutrients generated from independent biosynthetic pathways, and provide a novel example of the use of organ-specific gene silencing to improve the nutritional value of plant-derived products.

Breeding and biotechnology for improving berry nutritional quality

Breeding and biotechnological approaches are currently used to increase the content of specific bioactive components of plants, but the manipulation of plant metabolism is still not easy to address. There is an increasing awareness that multiple genetic and environmental factors affect production and accumulation of bioactive compounds, but these factors are rarely taken into account when fruit is marketed. Rigorous and unprejudiced evaluation of scientific evidence requires a defined set of criteria and methods of evaluation, particularly when breeding and biotech programs are aimed of producing new varieties with improved nutritional values combined with high plant production efficiency and fruit quality. In order to develop new genotypes and commercial cultivars the availability of new sources of Quality Attributes (QA) and Nutritional Attributes (NA) should be explored. In the strawberry, wild species such as F. virginiana glauca and F. vesca are good sources of bioactive compounds, but in raspberries the introduction of the wild germplasm (R. parvifolium) did not improve the nutritional quality of fruit. The methods available for detecting fruit TAC, combined with TPH and other quality parameters such as sugars, total acidity and fruit color, can be proposed as excellent tools for developing a fast and reliable program for screening large breeding populations for high nutritional quality genotypes. Furthermore, NA can represent a useful tool to facilitate analysis of "substantial equivalence" of transgenic and control derived fruit.