18 research outputs found
Genotypic variation in Actinidia deliciosa fruit size and carbohydrate content
In a global and increasingly competitive fresh produce market, more attention is being
given to fruit quality traits and consumer satisfaction. Kiwifruit occupies a niche
position in the worldwide market, when compared to apples, oranges or bananas. It is a
fruit with extraordinarily good nutritional traits, and its benefits to human health have
been widely described.
Until recently, international trade in kiwifruit was restricted to a single cultivar, but
different types of kiwifruit are now becoming available in the market. Effective
programmes of kiwifruit improvement start by considering the requirements of
consumers, and recent surveys indicate that sweeter fruit with better flavour are
generally preferred. There is a strong correlation between at-harvest dry matter and
starch content, and soluble solid concentration and flavour when fruit are eating ripe.
This suggests that carbon accumulation strongly influences the development of kiwifruit
taste.
The overall aim of the present study was to determine what factors affect carbon
accumulation during Actinidia deliciosa berry development. One way of doing this is by
comparing kiwifruit genotypes that differ greatly in their ability to accumulate dry
matter in their fruit. Starch is the major component of dry matter content. It was
hypothesized that genotypes were different in sink strength. Sink strength, by definition,
is the effect of sink size and sink activity.
Chapter 1 reviews fruit growth, kiwifruit growth and development and carbon
metabolism.
Chapter 2 describes the materials and methods used.
Chapter 3, 4, 5 and 6 describes different types of experimental work.
Chapter 7 contains the final discussions and the conclusions
Three Actinidia deliciosa breeding populations were analysed in detail to confirm that
observed differences in dry matter content were genetically determined. Fruit of the
different genotypes differed in dry matter content mainly because of differences in
starch concentrations and dry weight accumulation rates, irrespective of fruit size. More
detailed experiments were therefore carried out on genotypes which varied most in fruit
starch concentrations to determine why sink strengths were so different.
The kiwifruit berry comprises three tissues which differ in dry matter content. It was
initially hypothesised that observed differences in starch content could be due to a larger
proportion of one or other of these tissues, for example, of the central core which is
highest in dry matter content. The study results showed that this was not the case.
Sink size, intended as cell number or cell size, was then investigated. The outer pericarp
makes up about 60% of berry weight in âHaywardâ kiwifruit. The outer pericarp
contains two types of parenchyma cells: large cells with low starch concentration, and
small cells with high starch concentration. Large cell, small cell and total cell densities
in the outer pericarp were shown to be not correlated with either dry matter content or
fruit size but further investigation of volume proportion among cell types seemed
justified. It was then shown that genotypes with fruit having higher dry matter contents
also had a higher proportion of small cells. However, the higher proportion of small cell
volume could only explain half of the observed differences in starch content. So, sink
activity, intended as sucrose to starch metabolism, was investigated.
In transiently starch storing sinks, such as tomato fruit and potato tubers, a pivotal role
in carbon metabolism has been attributed to sucrose cleaving enzymes (mainly sucrose
synthase and cell wall invertase) and to ADP-glucose pyrophosphorylase (the
committed step in starch synthesis). Studies on tomato and potato genotypes differing in
starch content or in final fruit soluble solid concentrations have demonstrated a strong
link with either sucrose synthase or ADP-glucose pyrophosphorylase, at both enzyme
activity and gene expression levels, depending on the case. Little is known about
sucrose cleaving enzyme and ADP-glucose pyrophosphorylase isoforms. The
HortResearch Actinidia EST database was then screened to identify sequences
putatively encoding for sucrose synthase, invertase and ADP-glucose
pyrophosphorylase isoforms and specific primers were designed. Sucrose synthase,
invertase and ADP-glucose pyrophosphorylase isoform transcript levels were anlayzed
throughout fruit development of a selection of four genotypes (two high dry matter and
two low dry matter). High dry matter genotypes showed higher amounts of sucrose
synthase transcripts (SUS1, SUS2 or both) and higher ADP-glucose pyrophosphorylase
(AGPL4, large subunit 4) gene expression, mainly early in fruit development. SUS1-
like gene expression has been linked with starch biosynthesis in several crop (tomato,
potato and maize). An enhancement of its transcript level early in fruit development of
high dry matter genotypes means that more activated glucose (UDP-glucose) is
available for starch synthesis. This can be then correlated to the higher starch observed
since soon after the onset of net starch accumulation. The higher expression level of
AGPL4 observed in high dry matter genotypes suggests an involvement of this subunit
in drive carbon flux into starch. Changes in both enzymes (SUSY and AGPse) are then
responsible of higher starch concentrations. Low dry matter genotypes showed
generally higher vacuolar invertase gene expression (and also enzyme activity), early in
fruit development. This alternative cleavage strategy can possibly contribute to energy
loss, in that invertasesâ products are not adenylated, and further reactions and transport
are needed to convert carbon into starch. Although these elements match well with
observed differences in starch contents, other factors could be involved in carbon
metabolism control. From the microarray experiment, in fact, several kinases and
transcription factors have been found to be differentially expressed.
Sink strength is known to be modified by application of regulators. In âHaywardâ
kiwifruit, the synthetic cytokinin CPPU (N-(2-Chloro-4-Pyridyl)-N-Phenylurea)
promotes a dramatic increase in fruit size, whereas dry matter content decreases. The
behaviour of CPPU-treated âHaywardâ kiwifruit was similar to that of fruit from low dry
matter genotypes: dry matter and starch concentrations were lower. However, the CPPU
effect was strongly source limited, whereas in genotype variation it was not. Moreover,
CPPU-treated fruit gene expression (at sucrose cleavage and AGPase levels) was
similar to that in high dry matter genotypes. It was therefore concluded that CPPU
promotes both sink size and sink activity, but at different âspeedsâ and this ends in the
observed decrease in dry matter content and starch concentration. The lower âspeedâ in
sink activity is probably due to a differential partitioning of activated glucose between
starch storage and cell wall synthesis to sustain cell expansion.
Starch is the main carbohydrate accumulated in growing Actinidia deliciosa fruit.
Results obtained in the present study suggest that sucrose synthase and AGPase
enzymes contribute to sucrose to starch conversion, and differences in their gene
expression levels, mainly early in fruit development, strongly affect the rate at which
starch is therefore accumulated. This results are interesting in that starch and Actinidia
deliciosa fruit quality are tightly connected
VirusMINT: a viral protein interaction database
Understanding the consequences on host physiology induced by viral infection requires complete understanding of the perturbations caused by virus proteins on the cellular protein interaction network. The VirusMINT database (http://mint.bio.uniroma2.it/virusmint/) aims at collecting all protein interactions between viral and human proteins reported in the literature. VirusMINT currently stores over 5000 interactions involving more than 490 unique viral proteins from more than 110 different viral strains. The whole data set can be easily queried through the search pages and the results can be displayed with a graphical viewer. The curation effort has focused on manuscripts reporting interactions between human proteins and proteins encoded by some of the most medically relevant viruses: papilloma viruses, human immunodeficiency virus 1, EpsteinâBarr virus, hepatitis B virus, hepatitis C virus, herpes viruses and Simian virus 40
A manually annotated Actinidia chinensis var. chinensis (kiwifruit) genome highlights the challenges associated with draft genomes and gene prediction in plants
Most published genome sequences are drafts, and most are dominated by computational gene prediction. Draft genomes typically incorporate considerable sequence data that are not assigned to chromosomes, and predicted genes without quality confidence measures. The current Actinidia chinensis (kiwifruit) 'Hongyang' draft genome has 164\ua0Mb of sequences unassigned to pseudo-chromosomes, and omissions have been identified in the gene models
Phytohormone and Transcriptomic Analysis Reveals Endogenous Cytokinins Affect Kiwifruit Growth under Restricted Carbon Supply
Following cell division, fruit growth is characterized by both expansion through increases in cell volume and biomass accumulation in cells. Fruit growth is limited by carbon starvation; however, the mechanism controlling fruit growth under restricted carbohydrate supply is poorly understood. In a previous study using red-fleshed kiwifruit, we showed that long-term carbon starvation had detrimental effects on carbohydrate, anthocyanin metabolism, and fruit growth. To elucidate the mechanisms underlying the reduction in fruit growth during kiwifruit development, we integrated phytohormone profiling with transcriptomic and developmental datasets for fruit under high or low carbohydrate supplies. Phytohormone profiling of the outer pericarp tissue of kiwifruit showed a 6-fold reduction in total cytokinin concentrations in carbon-starved fruit, whilst other hormones were less affected. Principal component analysis visualised that cytokinin composition was distinct between fruit at 16 weeks after mid bloom, based on their carbohydrate supply status. Cytokinin biosynthetic genes (IPT, CYP735A) were significantly downregulated under carbon starvation, in agreement with the metabolite data. Several genes that code for expansins, proteins involved in cell wall loosening, were also downregulated under carbon starvation. In contrast to other fleshy fruits, our results suggest that cytokinins not only promote cell division, but also drive fruit cell expansion and growth in kiwifruit
Drymatter content and fruit size affect flavour and texture of novel Actinidia deliciosa genotypes
BACKGROUND: Previous studies with commercial kiwifruit cultivars have demonstrated that the taste of fruit with higher dry matter content (DM) is more liked by consumers. A unique replicated trial of kiwifruit genotypes (10 high/low DM Ă small/large-fruited genotypes) has provided an opportunity to consider how the genetic propensity for a kiwifruit to accumulate DM affects fruit flavour and texture. In the present study, eating-ripe fruit from each of the genotypes were assessed using a trained sensory panel and the relationships between these sensory attributes and fresh weight, DM, flesh firmness and soluble solids content (SSC) were explored.
RESULTS: The genotypes provided a diversity of flavour and texture attributes, each of which varied in perceived intensity of the sensory experience. High-DM genotypes had higher SSC and were perceived as sweeter than low-DM genotypes. Sweet taste was closely associated with the perception of the tropical flavour and high-DM genotypes were found to have more tropical notes. Fruit size was associated with fruit texture, and small fruit were characterised by a firmer and more fibrous core. Large high-DM fruit were perceived as juicier than those of all other genotypes.
CONCLUSIONS: Genotypes were perceived differently from one another, and differences in fruit size and DM content were reflected in fruit sensorial properties. This study is unique in demonstrating interactions between fruit size, DM and sensory properties. These findings could be relevant not only to kiwifruit but to fruiting crop breeders in general, because of the demonstrated potential for effects of fruit size and DM content on sweetness, flavour and fruit texture
Is fruit anatomy involved in variation in fruit starch concentration between Actinidia deliciosa genotypes?
Metabolic analysis of kiwifruit (Actinidia deliciosa) berries from extreme genotypes reveals hallmarks for fruit starch metabolism
Re-programming of Pseudomonas syringae pv. actinidiae gene expression during early stages of infection of kiwifruit
Abstract Background Pseudomonas syringae is a widespread bacterial species complex that includes a number of significant plant pathogens. Amongst these, P. syringae pv. actinidiae (Psa) initiated a worldwide pandemic in 2008 on cultivars of Actinidia chinensis var. chinensis. To gain information about the expression of genes involved in pathogenicity we have carried out transcriptome analysis of Psa during the early stages of kiwifruit infection. Results Gene expression in Psa was investigated during the first five days after infection of kiwifruit plantlets, using RNA-seq. Principal component and heatmap analyses showed distinct phases of gene expression during the time course of infection. The first phase was an immediate transient peak of induction around three hours post inoculation (HPI) that included genes that code for a Type VI Secretion System and nutrient acquisition (particularly phosphate). This was followed by a significant commitment, between 3 and 24 HPI, to the induction of genes encoding the Type III Secretion System (T3SS) and Type III Secreted Effectors (T3SE). Expression of these genes collectively accounted for 6.3% of the bacterial transcriptome at this stage. There was considerable variation in the expression levels of individual T3SEs but all followed the same temporal expression pattern, with the exception of hopAS1, which peaked later in expression at 48 HPI. As infection progressed over the time course of five days, there was an increase in the expression of genes with roles in sugar, amino acid and sulfur transport and the production of alginate and colanic acid. These are both polymers that are major constituents of extracellular polysaccharide substances (EPS) and are involved in biofilm production. Reverse transcription-quantitative PCR (RT-qPCR) on an independent infection time course experiment showed that the expression profile of selected bacterial genes at each infection phase correlated well with the RNA-seq data. Conclusions The results from this study indicate that there is a complex remodeling of the transcriptome during the early stages of infection, with at least three distinct phases of coordinated gene expression. These include genes induced during the immediate contact with the host, those involved in the initiation of infection, and finally those responsible for nutrient acquisition
Variation in carbon content and size in developing fruit of Actinidia deliciosa genotypes
Additional file 4: of A manually annotated Actinidia chinensis var. chinensis (kiwifruit) genome highlights the challenges associated with draft genomes and gene prediction in plants
BLASTP comparison of manually edited gene models to the revised âHongyangâ gene models. List of best reciprocal BLASTp matches between the revised Actinidia chinensis âHongyangâ genes [18]and the Red5 gene set (XLSX 436Â kb