Abstract
BackgroundTIR1-like proteins are F-box auxin receptors. Auxin binding to the F-box receptor proteins promotes the formation of SCFTIR1 ubiquitin ligase complex that targets the auxin repressors, Aux/IAAs, for degradation via the ubiquitin/26S proteasome pathway. The release of auxin response factors (ARFs) from their Aux/IAA partners allows ARFs to mediate auxin-responsive changes in downstream gene transcription. In an attempt to understand the potential role of auxin during fruit development, a plum auxin receptor, PslTIR1, has previously been characterized at the cellular, biochemical and molecular levels, but the biological significance of this protein is still lacking. In the present study, tomato (Solanum lycopersicum) was used as a model to investigate the phenotypic and molecular changes associated with the overexpression of PslTIR1.ResultsThe findings of the present study highlighted the critical role of PslTIR1 as positive regulator of auxin-signalling in coordinating the development of leaves and fruits. This was manifested by the entire leaf morphology of transgenic tomato plants compared to the wild-type compound leaf patterning. Moreover, transgenic plants produced parthenocarpic fruits, a characteristic property of auxin hypersensitivity. The autocatalytic ethylene production associated with the ripening of climacteric fruits was not significantly altered in transgenic tomato fruits. Nevertheless, the fruit shelf-life characteristics were affected by transgene presence, mainly through enhancing fruit softening rate. The short shelf-life of transgenic tomatoes was associated with dramatic upregulation of several genes encoding proteins involved in cell-wall degradation, which determine fruit softening and subsequent fruit shelf-life.ConclusionsThe present study sheds light into the involvement of PslTIR1 in regulating leaf morphology, fruit development and fruit softening-associated ripening, but not autocatalytic ethylene production. The results demonstrate that auxin accelerates fruit softening independently of ethylene action and this is probably mediated through the upregulation of many cell-wall metabolism genes.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-016-0746-z) contains supplementary material, which is available to authorized users.
Highlights
Genetic studies indicated that the AFB4-class of auxin receptors negatively regulates the auxin-response, unlike other members of the family that act as positive regulators [47, 50, 51]
The results suggested that PslAFB5 is more involved in flowering and early fruit development processes with minor contribution during fruit maturation and ripening; both PslTIR1 and PslAFB2 proteins play important roles in mediating overall reproductive growth development
The present study provides another line of evidence through the overexpression of a plum auxin receptor, PslTIR1, in tomato
Summary
Auxin bioassays highlight the pivotal role played by auxin in regulating the reproductive growth and the final fruit size through coordinating the abundant cell division and expansion that occurs after anthesis [10,11,12,13]. Fruit textural changes during ripening are associated with numerous modifications of the cell-wall architecture, leading to a reduction in intercellular adhesion, depolymerization and solubilization of pectins and hemicellulose, and loss of pectic galactose side chains [24, 25]. These modifications in cell-walls involve the coordinated and interdependent action of many cell-wall modifying enzymes and proteins. The exact molecular mechanisms by which auxin regulates these processes are not fully understood
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