Strawberry and beyond: a novel and comprehensive investigation of fruit maturation and ripening

A. Aharoni

Research output: Thesisinternal PhD, WU

Abstract

</strong></font><font size="3"><p>Functional-genomics tools such as Expressed Sequence Tags (ESTs) and whole genome sequencing, gene expression using macro and micro arrays and generation of mutant populations contributed largely to the research on model plants, mainly <em>Arabidopsis thaliana</em> . A substantial portion of this "tool-box" can also be utilized successfully for research on non-model plants, which are more difficult and time consuming to deal with, but allow investigations of unique biological processes such as fruit flavour biogenesis. As a first phase in a strategy to investigate strawberry fruit maturation and to identify key genes associated with fruit quality traits (in particularly aroma and flavour), we generated a collection of more than 1000 ESTs from ripe fruit cDNA library (cv. <em>Elsanta</em> ). Combining information on the putative identity of the ESTs and gene expression studies was subsequently used to select candidate genes for further investigation. In early studies we used RNA gel-blots to analyse levels of 50 selected genes (selected based on homology). More than 15 transcripts showed ripening - regulated expression pattern and included <em>FaMYB1</em> , a member of the R2R3 MYB family of transcription factors. The <em>FaMYB1</em> gene was subjected to a more profound investigation, and the results suggested it to function as repressor of late flavonoid biosynthesis genes in the ripe strawberry fruit. To perform a more comprehensive study of gene expression we constructed DNA microarrays representing 1700 strawberry cDNAs and compared gene expression both during fruit development and between receptacle and achene tissues. A major finding in this study was the identification of the <em>SAAT</em> gene encoding the ester-forming enzyme from strawberry. Volatile esters are major components of the aroma profiles of most fruit, including strawberry. We also generated a second, dedicated set of arrays, comprising only 384 probes selected on the basis of the first hybridisation results including mainly ripening regulated and receptacle associated cDNAs. This set was used to analyse gene expression in fruit treated with auxin and fruit under oxidative stress conditions. Taken as a whole, microarray experiments have provided us with an extensive and novel insight into the transcriptional programs active in strawberry fruit during maturation. They also led to the identification of several other flavour associated genes which are currently being characterised. As a complementary step for the large-scale analysis of gene expression using microarrays we conducted a set of experiments aimed at identifying key metabolic changes in strawberry fruit during development using a Fourier Transform Ion Cyclotron Mass Spectrometry (FTMS)-based method. The analysis identified changes in the levels of a large range of masses corresponding to known fruit metabolites and revealed novel information on the metabolic transition from immature to ripe fruit. The integration of emerging functional genomic practices will be an invaluable approach both for gene discovery and for understanding the biology of non-model plant species such as strawberry.
Original languageEnglish
QualificationDoctor of Philosophy
Awarding Institution
  • Wageningen University
Supervisors/Advisors
  • Mol, J.N.M., Promotor, External person
  • Stiekema, W.J., Promotor, External person
  • O'Connell, A.P., Promotor, External person
Award date16 Oct 2002
Place of PublicationS.l.
Print ISBNs9789058087256
Publication statusPublished - 2002

Keywords

  • fragaria
  • strawberries
  • ripening
  • maturation
  • gene expression
  • genomics
  • cum laude

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