Towards a virtual fruit focusing on quality: modelling features and potential uses

The fruit is a hierarchically organized organ composed of cells from different tissues. Its quality, defined by traits such as fruit size and composition, is the result of a complex chain of biological processes. These processes involve exchanges (transpiration, respiration, photosynthesis, phloem and xylem fluxes, and ethylene emission) between the fruit and its environment (atmosphere or plant), tissue differentiation, and cell functioning (division, endoreduplication, expansion, metabolic transformations, and vacuolar storage). In order to progress in our understanding of quality development, it is necessary to analyse the fruit as a system, in which processes interact. In this case, a process-based modelling approach is particularly powerful. Such a modelling approach is proposed to develop a future 'virtual fruit' model. The value of a virtual fruit for agronomists and geneticists is also discussed.     

Virtual profiling: a new way to analyse phenotypes

Simulation models can be used to perform virtual profiling in order to analyse eco‐physiological processes controlling plant phenotype. To illustrate this, an eco‐physiological model has been used to compare and contrast the status of a virtual fruit system under two situations of carbon supply. The model simulates fruit growth, accumulation of sugar, citric acid and water, transpiration, respiration and ethylene emission, and was successfully tested on peach (Prunus persica L. Batsch) for two leaf‐to‐fruit ratios (6 and 18 leaves per fruit). The development stage and the variation in leaf number had large effects of the fruit model variables dealing with growth, metabolism and fruit quality. A sensitivity analysis showed that changing a single parameter value, which could correspond to a genotypic change induced by a mutation, either strongly affects most of the processes, or affects a specific process or none. Correlation analysis showed that, in a complex system such as fruit, the intensity of many physiological processes and quality traits co‐varies. It also showed unexpected co‐variations resulting from emergent properties of the system. This virtual profiling approach opens a new route to explore the impact of mutations, or naturally occurring genetic variations, under differing environmental conditions.     

Simulating genotypic variation of fruit quality in an advanced peach x Prunus davidiana cross

Ecophysiological models are increasingly expected to describe genotypic variation within breeding populations. Accordingly, the ability of an ecophysiological model of peach to explain variation in fruit quality among 100 genotypes of a second backcross progeny derived from a clone of wild peach (Prunus davidiana) crossed with two commercial nectarine (Prunus persica) varieties was explored. Experimental measurements were carried out to calibrate the model for each genotype. The predictive quality of the model was tested on several independent datasets. The genotypic variation in dry and fresh growth of the fruit and the stone were effectively described by the model. Prediction of the amount of total sugar in flesh at maturity was accurate, whereas prediction of flesh dry matter content and total sugar concentration was suitable but less accurate. This approach and the results have allowed physiological processes to be ranked according to their contribution to the variation in fruit quality between genotypes. Fruit growth demand and the hydraulic conductance in the fruit were the main processes that explained the fruit quality variation. Shortcomings and further potential uses of the model are discussed.     

果实成熟和衰老的分子调控机制

成熟和衰老是果实生命周期中的两个重要阶段, 直接影响果实的品质保持及采后寿命。果实的成熟、衰老是一个复杂的生理过程, 受诸多内源因子的调控和外源因素的影响。该文重点综述近年来果实成熟、衰老分子机制方面的研究进展, 以及外源信号分子对果实成熟和衰老的调控作用。     

A model considering light reabsorption processes to correct in vivo chlorophyll fluorescence spectra in apples.

Chlorophyll-a contained in the peel of Granny Smith apples emits fluorescence upon excitation with blue light. The observed emission, collected by an external detector and corrected by its spectral response, is still distorted by light reabsorption processes taking place in the fruit skin and differs appreciably from the true spectral distribution of fluorescence emerging from chlorophyll molecules in the biological tissue. Reabsorption processes particularly affect the ratio of fluorescence intensities at 680 nm and at 730 nm. A model to obtain the correct spectral distribution of the emission, from the experimental fluorescence recorded at a fluorometer detector and corrected for the detector spectral sensitivity, is developed in the present work. Measurements of the whole fruit reflectance, the peel transmittance and the flesh reflectance allow the calculation of the reabsorption-corrected spectra. The model is validated by comparing the corrected emission spectra with that obtained for a thin layer of apple-peel-chloroplasts, where no reabsorption takes place. It is recommended to correct distortions in emission spectra of intact fruits due to light reabsorption effects whenever a correlation between the physiological state of the fruit and its fluorescence spectra is investigated.     

QualiTree, a virtual fruit tree to study the management of fruit quality. I. Model development

This article presents QualiTree, a generic fruit tree model that can simulate the effects of various cultivation practices on the development and within-tree variability of fruit quality. These practices include fruit thinning, summer and winter pruning, irrigation and tree training. Combining both agronomic and physiology viewpoints, the model describes the tree as a set of objects??fruiting units organised into a tree architecture and viewed in detail, and other compartments viewed globally??that exchange carbon and are the targets of physiological functions that can be changed by cultivation practices. The complex effect of shoot removal on tree behaviour was subjected to a special modelling effort using the coordination theory. QualiTree combines existing models of fruit quality development and simple carbon allocation functions. Though parsimonious, it is able to express a high degree of variability of fruit quality criteria. Future developments of QualiTree relative to an extension of the range of fruit quality criteria and the effects of cultivation practices are also discussed.     

Insights into fruit function from the proteome of the hypanthium

Apple (Malus×domestica Borkh.) was used as a model to studying essential biological processes occurring in mature fruit hypanthium, commonly referred to as the fruit flesh or pulp, a highly active tissue where numerous metabolic processes such as carbohydrate metabolism and signal transduction occur. To understand the complex biological processes occurring in the hypanthium, a proteomics approach was used to analyze the proteome from freshly harvested ripe apple fruits. A total of 290 well-resolved spots were detected using two-dimensional gel electrophoresis (2-DE). Out of these, 216 proteins were identified representing 116 non-redundant proteins using matrix-assisted laser-desorption ionisation time-of-flight mass spectrometry (MALDI-TOF MS) and either the MASCOT or ProteinProspector engine for peptide mass fingerprinting (PMF) database searching. Identified proteins were classified into 13 major functional categories. Among these, the energy metabolism class was the most represented and included 50% of proteins homologous to Arabidopsis proteins that are involved in the response to biotic and abiotic stresses, suggesting a dual role for these proteins in addition to energy metabolism. We also identified dynein heavy chain in the hypanthium although this protein has been proposed as absent from angiosperms and thus suggest that the lack of dyneins in higher plants studied to date may not be a general characteristic to angiosperm genomic organisation. We therefore conclude that the detection and elucidation of the apple hypanthium proteome is an indispensable step towards the comprehension of fruit metabolism, the integration of genomic, proteomic and metabolomic data to agronomic trait information and thus fruit quality improvements.     

果树代谢组学研究进展

果树代谢组学是继基因组学、蛋白质组学之后又一新兴的组学技术,主要是从代谢水平研究果树整体或局部代谢物变化差异,帮助发现新功能基因和了解代谢网络。目前果树代谢组学研究刚刚起步,相关研究相对较少,该文介绍了果树代谢组学的主要研究内容与方法以及在果树上的相关应用。     

Persistent infection and promiscuous recombination of multiple genotypes of an RNA virus within a single host generate extensive diversity

Recombination and reassortment of viral genomes are major processes contributing to the creation of new, emerging viruses. These processes are especially significant in long-term persistent infections where multiple viral genotypes co-replicate in a single host, generating abundant genotypic variants, some of which may possess novel host-colonizing and pathogenicity traits. In some plants, successive vegetative propagation of infected tissues and introduction of new genotypes of a virus by vector transmission allows for viral populations to increase in complexity for hundreds of years allowing co-replication and subsequent recombination of the multiple viral genotypes. Using a resequencing microarray, we examined a persistent infection by a Citrus tristeza virus (CTV) complex in citrus, a vegetatively propagated, globally important fruit crop, and found that the complex comprised three major and a number of minor genotypes. Subsequent deep sequencing analysis of the viral population confirmed the presence of the three major CTV genotypes and, in addition, revealed that the minor genotypes consisted of an extraordinarily large number of genetic variants generated by promiscuous recombination between the major genotypes. Further analysis provided evidence that some of the recombinants underwent subsequent divergence, further increasing the genotypic complexity. These data demonstrate that persistent infection of multiple viral genotypes within a host organism is sufficient to drive the large-scale production of viral genetic variants that may evolve into new and emerging viruses.     

Ecophysiological analysis of genotypic variation in peach fruit growth

Cultivated varieties generally differ greatly from wild genotypes of the same closely related species. However, the processes responsible for these differences have not been elucidated. To analyse variations in fruit mass, fruit growth was characterized in a peach cultivar, a wild related species non-cultivated, and four hybrids derived by crossing them. These genotypes offer a wide range of agronomic values. An ecophysiological model of peach fruit growth in dry mass was used. This model simulates carbon partitioning at the 'shoot-bearing fruit' level by considering three compartments: fruits, 1-year-old stems and leafy shoots. The experimental measurements showed considerable variation between genotypes for fruit mass at maturity, fruit growth and source activity. The parameters of the ecophysiological model for each genotype were estimated from experimental data,. The model made it possible to account for genotypic variations in fruit growth and for genotype x fruit load interactions. Using the model, it was shown that the main processes explaining fruit growth variations among the genotypes studied were differences in potential fruit growth.     

Fruit size: Towards an understanding of the metabolic control of fruit growth using avocado as a model system

Final fruit size is the consequence of complex metabolic events that occur between fruit set and maturation. Disruption of these biochemical and molecular processes at any stage during fruit growth will impact on final fruit size. Because fruit size is a function of cell number rather than cell size, factors affecting cell division cycle activity assume importance. In this paper, we focus attention on the metabolic control of fruit growth using avocado as a model system. Three areas of current interest are highlighted, viz. the contribution by isoprenoid metabolism in the control of cell proliferation, the role played by carbohydrate content and composition in signalling changes in metabolite status and gene expression and maintenance of plant hormone homeostasis. Central to the process of fruit growth and control of final fruit size by cell division is 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGR) and activity of the sucrose non-fermenting 1-related protein kinase (SnRK1) complex. It is argued that sugar content and composition of sink cells impact on SnRK1 (and hexokinase) to modulate expression of sugar-metabolizing enzymes, HMGR and molybdenum cofactor (MoCo)-containing enzymes. These changes, in turn, impact on hormone metabolism by affecting allocation of the purine-derived MoCo to aldehyde oxidase and thus the endogenous concentration of indole-3-acetic acid, abscisic acid and cytokinin (CK) to alter plant hormone homeostasis. These aspects are integrated into a model to explain the metabolic control of avocado fruit growth and final fruit size.     

Model-assisted analysis of tomato fruit growth in relation to carbon and water fluxes

This work proposed a model of tomato growth adapted from the Fishman and Génard model developed to predict carbon and water accumulation in peach fruit. The main adaptations relied on the literature on tomato and mainly concerned: (i) the decrease in cell wall extensibility coefficient during fruit development; (ii) the increase in the membrane reflection coefficient to solute from 0 to 1, which accounted for the switch from symplasmic to apoplasmic phloem unloading, and (iii) the negative influence of the initial fruit weight on the maximum rate of active carbon uptake based on the assumption of higher competition for carbon among cells in large fruits containing more cells. A sensitivity analysis was performed and the model was calibrated and evaluated with satisfaction on 17 experimental datasets obtained under contrasting environmental (temperature, air vapour pressure deficit) and plant (plant fruit load and fruit position) conditions. Then the model was used to analyse the variations in the main fluxes involved in tomato fruit growth and accumulation of carbon in response to virtual carbon and water stresses. The conclusions are that this model, integrating simple biophysical laws, was able to simulate the complex fruit behaviour in response to external or internal factors and thus it may be a powerful tool for managing fruit growth and quality.     

Impact of introduction of Bactrocera dorsalis (Diptera: Tephritidae) and classical biological control releases of Fopius arisanus (Hymenoptera: Braconidae) on economically important fruit flies in French Polynesia

Oriental fruit fly, Bactrocera dorsalis (Hendel) (Diptera: Tephritidae), was discovered on Tahiti Island in July 1996. Eradication programs were conducted from 1997 to 2001, but failed. From 1998 to 2006, B. dorsalis was recovered from 29 different host fruit from the five Society Islands: Tahiti, Moorea, Raiatea, Tahaa, and Huahine. Analysis of coinfestation patterns by B. dorsalis, Bactrocera tryoni (Froggatt), and Bactrocera kirki (Froggatt) suggested B. dorsalis had displaced these two species and become the most abundant fruit fly in coastal areas. To suppress B. dorsalis populations, a classical biological control program was initiated to introduce the natural enemy Fopius arisanus (Sonan) (Hymenoptera: Braconidae) into French Polynesia from Hawaii. Wasps were released and established on Tahiti, Moorea, Raiatea, Tahaa, and Huahine Islands. In guava, Psidium guajava L., collections for Tahiti, F. arisanus parasitism of fruit flies was 2.1, 31.8, 37.5, and 51.9% for fruit collected for 2003, 2004, 2005 and 2006, respectively. Based on guava collections in 2002 (before releases) and 2006 (after releases), there was a subsequent decrease in numbers of B. dorsalis, B. tryoni, and B. kirki fruit flies emerging (per kilogram of fruit) by 75.6, 79.3, and 97.9%, respectively. These increases in F. arisanus parasitism and decreases in infestation were similar for other host fruit. Establishment of F. arisanus is the most successful example of classical biological control of fruit flies in the Pacific area outside of Hawaii and serves as a model for introduction into South America, Africa, and China where species of the B. dorsalis complex are established.     

Ethylene and fruit ripening

The latest advances in our understanding of the relationship between ethylene and fruit ripening are reviewed. Considerable progress has been made in the characterisation of genes encoding the key ethylene biosynthetic enzymes, ACC synthase (ACS) and ACC oxidase (ACO) and in the isolation of genes involved in the ethylene signal transduction pathway, particularly those encoding ethylene receptors ( ETR ). These have allowed the generation of transgenic fruit with reduced ethylene production and the identification of the Nr tomato ripening mutant as an ethylene receptor mutant. Through these tools, a clearer picture of the role of ethylene in fruit ripening is now emerging. In climacteric fruit, the transition to autocatalytic ethylene production appears to result from a series of events where developmentally regulated ACO and ACS gene expression initiates a rise in ethylene production, setting in motion the activation of autocatalytic ethylene production. Differential expression of ACS and ACO gene family members is probably involved in such a transition. Finally, we discuss evidence suggesting that the NR ethylene perception and transduction pathway is specific to a defined set of genes expressed in ripening climacteric fruit and that a distinct ETR pathway regulates other ethylene-regulated genes in both immature and ripening climacteric fruit as well as in non-climacteric fruit. The emerging picture is one where both ethylene-dependent and -independent pathways coexist in both climacteric and non-climacteric fruits. Further work is needed in order to dissect the molecular events involved in individual ripening processes and to understand the regulation of the expression of both ethylene-dependent and -independent genes.     

Whole-genome expression analysis: challenges beyond clustering.

Measuring the expression of most or all of the genes in a biological system raises major analytic challenges. A wealth of recent reports uses microarray expression data to examine diverse biological phenomena - from basic processes in model organisms to complex aspects of human disease. After an initial flurry of methods for clustering the data on the basis of similarity, the field has recognized some longer-term challenges. Firstly, there are efforts to understand the sources of noise and variation in microarray experiments in order to increase the biological signal. Secondly, there are efforts to combine expression data with other sources of information to improve the range and quality of conclusions that can be drawn. Finally, techniques are now emerging to reconstruct networks of genetic interactions in order to create integrated and systematic models of biological systems.     

Spatial and temporal variations in mango colour,acidity, and sweetness in relation to temperature and ethylene gradients within the fruit

Managing fruit quality is complex because many different attributes have to be taken into account, which are themselves subjected to spatial and temporal variations. Heterogeneous fruit quality has been assumed to be partly related to temperature and maturity gradients within the fruit.     

植物激素对果树单性结实调控的研究进展

尽管种子与果实的发育过程密切相关,但由于无籽果实提高了果实的品质并延长了货架期,因此无籽果实受到生产者和消费者的广泛青睐。果实的生长受激素调控,而相关研究也初步揭示了激素在单性结实果实形成过程中的作用。本文对单性结实的概念、诱导单性结实的激素种类及功能、诱导机理,以及转基因技术在单性结实果实生产中的应用概况进行了综述,以期为果树单性结实的研究提供参考。     

Recent Advances in the Regulation of Citric Acid Metabolism in Citrus Fruit

The regulation of citric acid metabolism during fruit ripening has a major impact on the production of high-quality fruit. The impact of citric acid on organoleptic fruit quality attributes, fruit storage performance and the synthesis of several secondary metabolites has led to an exponential increase in research efforts during the last two decades. Recent research has focused on the relationship among citric acid biosynthesis, transportation, storage, and utilization. Among citrate metabolic processes, activities of a proton pump, especially the plasma membrane H⁺-ATPase on tonoplast and citrate catabolism in cytosol play important roles in the regulation of citrate accumulation in cell vacuoles. Moreover, we highlight recent advances and provide an overview of citrate metabolism, postharvest physiology of citrate metabolism, and the influence of agro-climatic factors on citrus fruits. It is the first review that provides a comprehensive model for citrate metabolism in citrus fruit juice sacs. We anticipate that this model for the regulation of citrate metabolism will facilitate the study of fruit acidity in citrus and other nonclimacteric fruits.