Light Microclimate-Driven Changes at Transcriptional Level in Photosynthetic Grape Berry Tissues.

Andreia Garrido,Artur Conde,Ric C H De Vos,Ana Cunha

doi:10.3390/plants10091769

Abstract

Viticulture practices that change the light distribution in the grapevine canopy can interfere with several physiological mechanisms, such as grape berry photosynthesis and other metabolic pathways, and consequently impact the berry biochemical composition, which is key to the final wine quality. We previously showed that the photosynthetic activity of exocarp and seed tissues from a white cultivar (Alvarinho) was in fact responsive to the light microclimate in the canopy (low and high light, LL and HL, respectively), and that these different light microclimates also led to distinct metabolite profiles, suggesting a berry tissue-specific interlink between photosynthesis and metabolism. In the present work, we analyzed the transcript levels of key genes in exocarps and seed integuments of berries from the same cultivar collected from HL and LL microclimates at three developmental stages, using real-time qPCR. In exocarp, the expression levels of genes involved in carbohydrate metabolism (VvSuSy1), phenylpropanoid (VvPAL1), stilbenoid (VvSTS1), and flavan-3-ol synthesis (VvDFR, VvLAR2, and VvANR) were highest at the green stage. In seeds, the expression of several genes associated with both phenylpropanoid (VvCHS1 and VvCHS3) and flavan-3-ol synthesis (VvDFR and VvLAR2) showed a peak at the véraison stage, whereas that of RuBisCO was maintained up to the mature stage. Overall, the HL microclimate, compared to that of LL, resulted in a higher expression of genes encoding elements associated with both photosynthesis (VvChlSyn and VvRuBisCO), carbohydrate metabolism (VvSPS1), and photoprotection (carotenoid pathways genes) in both tissues. HL also induced the expression of the VvFLS1 gene, which was translated into a higher activity of the FLS enzyme producing flavonol-type flavonoids, whereas the expression of several other flavonoid pathway genes (e.g., VvCHS3, VvSTS1, VvDFR, and VvLDOX) was reduced, suggesting a specific role of flavonols in photoprotection of berries growing in the HL microclimate. This work suggests a possible link at the transcriptional level between berry photosynthesis and pathways of primary and secondary metabolism, and provides relevant information for improving the management of the light microenvironment at canopy level of the grapes.

Highlights

Grapevine (Vitis vinifera L.) is commonly cultivated across temperate to semi-dry areas, including the Mediterranean region [1,2]
The results obtained in this study corroborate those of our previous studies [31,32], suggesting that tissue-specific photosynthesis coincides with the expression of photosynthesis and sucrose synthesis-related genes, and to the gene transcription and enzyme activities of key steps in secondary metabolism
The berries have a relatively high demand for carbon and energy to sustain their high growth rate, and the main part of the sucrose imported through the dorsal vascular system is used to meet that demand: the relatively high levels of transcripts of genes involved in sucrose catabolism (VvSuSy1), combined with the low levels of VvSPS1 in the exocarp, may support our hypothesis that photosynthesis contributes energy to that unloading process

Summary

Introduction

Grapevine (Vitis vinifera L.) is commonly cultivated across temperate to semi-dry areas, including the Mediterranean region [1,2]. Grape berry is composed of different tissues and cell layers, including the exocarp (skin), mesocarp (pulp), and seeds, which present distinct anatomical characteristics and biochemical profiles during development [4,5,6]. The seed is rich in flavan-3-ol monomers and procyanidins (tannins), which confer protection against herbivory but are responsible for the bitterness and astringency of the wine [11]. Both primary and secondary metabolites of grape berry tissues are extremely important for fruit nutritional and organoleptic characteristics [12]. Complex regulatory mechanisms are involved in their synthesis, such as many transcriptional, translational and biochemical mechanisms, which can be modulated by biotic and abiotic factors (as reviewed by Serrano et al [13])

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