Browsing by Author "Kuhn, Nathalie"

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    Color desynchronization with softening of 'Hass' avocado: Targeted pigment, hormone and gene expression analysis
    (2022) Arancibia-Guerra, Camila; Nunez-Lillo, Gerardo; Caceres-Mella, Alejandro; Carrera, Esther; Meneses, Claudio; Kuhn, Nathalie; Pedreschi, Romina
    Main determinants of 'Hass' avocado quality and consumer acceptance are mesocarp firmness and skin color. Relevant producing and exporting countries have evidenced during the last seasons color desynchronization with softening at edible ripeness. The mechanisms driving this desynchronization are still unknown. Thus, this study aimed to provide a first deep insight into this problem by combining targeted pigment, hormone and gene expression analysis in avocado exocarp samples from different harvests and storage conditions. Results showed that color desynchronization was more pronounced in regular air (RA) condition and early harvest for all or-chards. Prolonged controlled atmosphere (CA) storage synchronized color development in all orchards analyzed. Chlorophylls and carotenoids did not decrease in content as the fruit reached the ready to eat stage but remained stable while total anthocyanins increased in all evaluated orchards. Total anthocyanins and abscisic acid were strongly and positively correlated with the "black color" phenotype. The other evaluated hormones (JA, IAA, SA, tZ, DHZ, iP) revealed negative correlations with the "black color" phenotype. Gene expression related to the ethylene biosynthesis pathway (PamACS, PamETR avocado gene orthologues) showed an up-regulation in fruit phenotyped as ready to eat (RTE) Green. In addition, the expression of the genes orthologues PamPAL, PamF3H and PamCHS was also positively correlated with anthocyanin content in the skin. Our results revealed that color desynchronization with softening of 'Hass' avocado is quite complex in terms of hormonal interplay and the role of storage conditions (RA vs CA). Thus, further studies need broader approaches such as the incorporation of omics studies to elucidate the physiological and molecular mechanisms driving color desynchronization.
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    The Glucose-Related Decrease in Polar Auxin Transport During Ripening and its Possible Role in Grapevine Berry Coloring
    (2023) Serrano, Alejandra; Kuhn, Nathalie; Restovic, Franko; Meyer-Regueiro, Carlos; Madariaga, Mónica; Arce Johnson, Jorge Patricio
    Auxin is a hormone that delays ripening in part by reducing anthocyanin content and impairing color development. Auxin content declines during the ripening process, whereas sugars accumulate from pre-veraison onwards. The spatio-temporal distribution of this hormone depends in part on polar auxin transport. On the other hand, sugar, acting as a signal molecule, modulates auxin distribution in model organisms; however, its efect on polar auxin transport during the coloring process in grapevine berries has not been investigated. To address this issue, we characterized auxin transport and sugar variations during the ripening process and performed treatments intended to alter auxin homeostasis in grape fruits. We found that polar auxin transport declines in concert with increasing sugar content prior to and at veraison. Moreover, N-1-napthylphthalamic acid (NPA; a polar auxin transport inhibitor) and glucose treatment increased berry coloration, reduced polar auxin transport and VvPIN1 transcript abundance at pre-veraison, and combined NPA and glucose treatment further increased berry color compared to glucose and NPA alone. Indole-3-acetic acid (IAA) treatment prevented the negative efect of glucose on auxin transport, suggesting that auxin homeostasis might be relevant for glucose modulation of berry ripening in grapevine. Impaired auxin transport is associated with increased ethylene sensitivity in several plant processes, including fruit abscission. For exploring a potential involvement of the ethylene pathway during the coloring process, we analyzed the transcript abundance of the putative ethylene receptor, VvETR2, a possible negative regulator of the ethylene pathway. We found that glucose plus NPA treatment reduced VvETR2 transcript abundance, whose expression is reported to decline from veraison onwards. Our results suggest a possible mechanism in which a rise in glucose contributes to auxin transport inhibition in coloring berries. As glucose has been reported to promote ripening and IAA inhibits berry coloring, our results further support an antagonistic switch between IAA and glucose, that could also involve changes in the expression of the VvETR2 gene
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    The role of auxin during early berry development in grapevine as revealed by transcript profiling from pollination to fruit set
    (2021) Godoy, Francisca; Kuhn, Nathalie; Munoz, Mindy; Marchandon, German; Gouthu, Satyanarayana; Deluc, Laurent; Delrot, Serge; Lauvergeat, Virginie; Arce-Johnson, Patricio
    Auxin is a key phytohormone that modulates fruit formation in many fleshy fruits through the regulation of cell division and expansion. Auxin content rapidly increases after pollination and the manipulation in its levels may lead to the parthenocarpic development. ln Vitis vinifera L., little is known about the early fruit development that encompasses from pollination to fruit set. Pollination/fertilization events trigger fruit formation, and auxin treatment mimics their effect in grape berry set. However, the role of auxin in this process at the molecular level is not well understood. To elucidate the participation of auxin in grapevine fruit formation, morphological, reproductive, and molecular events from anthesis to fruit set were described in sequential days after pollination. Exploratory RNA-seq analysis at four time points from anthesis to fruit set revealed that the highest percentage of genes induced/repressed within the hormone-related gene category were auxin-related genes. Transcript profiling showed significant transcript variations in auxin signaling and homeostasis-related genes during the early fruit development. Indole acetic acid and several auxin metabolites were present during this period. Finally, application of an inhibitor of auxin action reduced cell number and the mesocarp diameter, similarly to unpollinated berries, further confirming the key role of auxin during early berry development. This work sheds light into the molecular features of the initial fruit development and highlights the auxin participation during this stage in grapevine.