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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.

In sweet cherry, as in most non-climacteric species, abscisic acid (ABA) plays a major role in the control of fruit ripening and color development. Although the ABA treatment of sweet cherry fruits has been reported to upregulate anthocyanin pathway-related genes or ABA pathway-related genes, the temporality of molecular and physiological events occurring during color development and the ABA control of these events during the color initiation are lacking in this species. In this work, we analyzed variations in the Index of Absorbance Difference (IAD), a maturity index, and total anthocyanins along with changes in transcript abundance of ABA and anthocyanin pathway-related genes, from light green to red fruit stages. PavNCED1 and ABA signaling pathway-related genes upregulated when fruits transitioned from light green to pink stage, whereas anthocyanin pathway-related transcripts increased from pink to the red stage, together with increases in the anthocyanin content and IAD, suggesting sequentiality in molecular and physiological events during color development. Additionally, ABA applied at color initiation in planta advanced IAD, increased anthocyanin content, and yielded darker fruits at harvest. These changes were accompanied by changes in the transcript accumulation of ABA and anthocyanin pathway-related genes. This in planta treatment of sweet cherry fruits with ABA confirms that ABA is a central player in the control of color initiation in sweet cherries, associated with the transcript accumulation of genes involved in ABA homeostasis and signaling, which is followed by the up-regulation of anthocyanin pathway-related genes and color development.

Berry formation is the process of ovary conversion into a functional fruit, and is characterized by abrupt changes in the content of several phytohormones, associated with pollination and fertilization. Much effort has been made in order to improve our understanding of berry development, particularly from veraison to post-harvest time. However, the period of berry formation has been poorly investigated, despite its importance. Phytohormones are involved in the control of fruit formation; hence it is important to understand the regulation of their content at this stage. Grapevine is an excellent fleshy-fruit plant model since its fruits have particularities that differentiate them from those of commonly studied organisms. For instance, berries are prepared to cope with stress by producing several antioxidants and they are non-climacteric fruits. Also its genome is fully sequenced, which allows to identify genes involved in developmental processes. In grapevine, no link has been established between pollination and phytohormone biosynthesis, until recently. Here we highlight relevant findings regarding pollination effect on gene expression related to phytohormone biosynthesis, and present results showing how quickly this effect is achieved.

International audience; Grapevine (Vitis vinifera L.) is a non-climacteric fruit species used as table fruit, dried raisins, and for vinification (wines) and distillation (liquors). In recent years, our knowledge of the molecular basis of ripening regulation has improved. Water status, light conditions, and temperature may hasten, delay, or enhance ripening. Hormones seem to play a central role, as their concentrations change prior to and during ripening and in response to several environmental cues. The review summarizes recent data related to the molecular and hormonal control of grape berry development and ripening, with special emphasis on secondary metabolism and its response to the environment, and pinpoints some experimental limitations.

Background Indole-3-acetic acid (IAA), the most abundant auxin, is a growth promoter hormone involved in several developmental processes. Auxin homeostasis is very important to its function and this is achieved through the regulation of IAA biosynthesis, conjugation, degradation and transport. In grapevine, IAA plays an essential role during initial stages of berry development, since it delays fruitlet abscission by reducing the ethylene sensitivity in the abscission zone. For this reason, Continuous polar IAA transport to the pedicel is required. This kind of transport is controlled by IAA, which regulates its own movement by modifying the expression and localization of PIN-FORMED (PIN) auxin efflux facilitators that localize asymmetrically within the cell. On the other hand, the hormone gibberellin (GA) also activates the polar auxin transport by increasing PIN stability. In Vitis vinifera, fruitlet abscission occurs during the first two to three weeks after flowering. During this time, IAA and GA are present, however the role of these hormones in the control of polar auxin transport is unknown. Results In this work, the use of radiolabeled IAA showed that auxin is basipetally transported during grapevine fruitlet abscission. This observation was further supported by immunolocalization of putative VvPIN proteins that display a basipetal distribution in pericarp cells. Polar auxin transport and transcripts of four putative VvPIN genes decreased in conjunction with increased abscission, and the inhibition of polar auxin transport resulted in fruit drop. GA3 and IAA treatments reduced polar auxin transport, but only GA3 treatment decreased VvPIN transcript abundance. When GA biosynthesis was blocked, IAA was capable to increase polar auxin transport, suggesting that its effect depends on GA content. Finally, we observed significant changes in the content of several IAA-related compounds during the abscission period. Conclusions These results provide evidence that auxin homeostasis plays a central role during grapevine initial fruit development and that GA and IAA controls auxin homeostasis by reducing polar auxin transport. Electronic supplementary material The online version of this article (doi:10.1186/s12870-016-0914-1) contains supplementary material, which is available to authorized users.