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JXB Advance Access published online on January 6, 2009
Journal of Experimental Botany, doi:10.1093/jxb/ern336
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© 2009 The Author(s).
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-commercial License (http://creativecommons.org/licences/by-nc/2.0/uk) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. This paper is available online free of all access charges (see http://jxb.oxfordjournals.org/open_access.html for further details)

RESEARCH PAPER

Post-veraison sunlight exposure induces MYB-mediated transcriptional regulation of anthocyanin and flavonol synthesis in berry skins of Vitis vinifera

José Tomás Matus1, Rodrigo Loyola2, Andrea Vega2, Alvaro Peña-Neira3, Edmundo Bordeu1, Patricio Arce-Johnson2,* and José Antonio Alcalde1,*

1Departamento de Fruticultura y Enología, Pontificia Universidad Católica de Chile, Av. Vicuña Mackenna 4560, Santiago, Chile
2Departamento de Genética Molecular y Microbiología, Pontificia Universidad Católica de Chile, Av. Alameda 340, PO Box 114-D, Santiago, Chile
3Departamento de Agroindustria y Enología, Facultad de Ciencias Agronómicas, Universidad de Chile Santiago, Chile

* To whom correspondence should be addressed: E-mail: parce{at}bio.puc.cl or jalcalde{at}uc.cl

Anthocyanins, flavan-3-ols, and flavonols are the three major classes of flavonoid compounds found in grape berry tissues. Several viticultural practices increase flavonoid content in the fruit, but the underlying genetic mechanisms responsible for these changes have not been completely deciphered. The impact of post-veraison sunlight exposure on anthocyanin and flavonol accumulation in grape berry skin and its relation to the expression of different transcriptional regulators known to be involved in flavonoid synthesis was studied. Treatments consisting of removing or moving aside the basal leaves which shade berry clusters were applied. Shading did not affect sugar accumulation or gene expression of HEXOSE TRANSPORTER 1, although in the leaf removal treatment, these events were retarded during the first weeks of ripening. Flavonols were the most drastically reduced flavonoids following shading and leaf removal treatments, related to the reduced expression of FLAVONOL SYNTHASE 4 and its putative transcriptional regulator MYB12. Anthocyanin accumulation and the expression of CHS2, LDOX, OMT, UFGT, MYBA1, and MYB5a genes were also affected. Other regulatory genes were less affected or not affected at all by these treatments. Non-transcriptional control mechanisms for flavonoid synthesis are also suggested, especially during the initial stages of ripening. Although berries from the leaf removal treatment received more light than shaded fruits, malvidin-3-glucoside and total flavonol content was reduced compared with the treatment without leaf removal. This work reveals that flavonol-related gene expression responds rapidly to field changes in light levels, as shown by the treatment in which shaded fruits were exposed to light in the late stages of ripening. Taken together, this study establishes MYB-specific responsiveness for the effect of sun exposure and sugar transport on flavonoid synthesis.

Key words: bHLH, flavonoids, grape, leaf removal, MYB12, PAR, sugar, source, sink, WDR

Received 7 November 2008; Accepted 26 November 2008


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