Grape berry responses to sequential flooding and heatwave events: a physiological, transcriptional, and metabolic overview

Grapevine cultivation, such as the whole horticulture, is currently challenged by several factors, among which the extreme weather events occurring under the climate change scenario are the most relevant. Within this context, the present study aims at characterizing at the berry level the physiological response of Vitis vinifera cv. Sauvignon Blanc to sequential stresses simulated under a semi-controlled environment: flooding at bud-break followed by multiple summer stress (drought plus heatwave) occurring at pre-vèraison. Transcriptomic and metabolomic assessments were performed through RNASeq and NMR, respectively. A comprehensive hormone profiling was also carried out. Results pointed out a different response to the heatwave in the two situations. Flooding caused a developmental advance, determining a different physiological background in the berry, thus affecting its response to the summer stress at both transcriptional levels, with the upregulation of genes involved in oxidative stress responses, and metabolic level, with the increase in osmoprotectants, such as proline and other amino acids. In conclusion, sequential stress, including a flooding event at bud-break followed by a summer heatwave, may impact phenological development and berry ripening, with possible consequences on berry and wine quality. A berry physiological model is presented that may support the development of sustainable vineyard management solutions to improve the water use efficiency and adaptation capacity of actual viticultural systems to future scenario

Ripening behavior in red flesh ‘Kissabel®’ apple fruit during postharvest

In the last few years, the cultivation of red flesh apple cultivars received great attention due to their novelty and valuable nutraceutical properties, considering their higher anthocyanin and phenols content than white flesh apple cultivars. Nevertheless, red flesh cultivars can be characterized by a low storability, being therefore prone to develop internal browning disorder. In this preliminary work, we investigated the postharvest ripening behavior of the red flesh apple R201-‘Kissabel®’, a late season cultivar, in comparison with the white pulp apple ‘Golden Delicious’, generally considered as the standard reference cultivar for apple. For this purpose, fruit were collected at commercial harvest and kept for one month at room temperature in regular atmosphere. The cortex of five apple was sampled every two days along this period. Total RNA was extracted, reverse transcribed and RT-qPCR were performed on specific ripening related genes, such as ethylene biosynthetic genes (MdACS3, MdACS1 and MdACO1) and the polygalacturonase-1 (MdPG1). Moreover, proton-transferreaction mass spectrometry (PTR-ToF-MS) was employed to quantify ethylene evolution during the stored period. In ‘Kissabel®’, ethylene started to be accumulated immediately after harvest, and one week earlier than ‘Golden Delicious’. Moreover, both cultivars showed a first peak at 9 and 16 days after harvest (DAH) and a second one at 14 and 21 DHA, respectively. Based on the expression profile of selected genes, the first peak coincided with the ripening onset. In ‘Golden Delicious’, indeed, the highest expression level, for all genes, corresponded with the maximum of ethylene production at 16 DAH. In ‘Kissabel®’ the maximum expression was instead detected two days earlier respect the ethylene burst, while the expression pattern of MdACS3 decreased immediately after harvest in both cultivars, as expected. These results represent the first step to better characterize the ripening behavior and storability of this new apple cultiva

Apple (Malus domestica L. Borkh) as an emerging model for fruit development

Apple research has undergone great improvements in the last years, in both quantitative and qualitative terms. Huge amount of data are now available, especially as far as the early development and the ripening phase are concerned. Moreover, the recent release of the apple genome sequence is significantly speeding up research, allowing on one hand to shed light on the most critical aspects of fruit development with almost immediate practical implications and, on the other hand, to identify new molecular markers that will improve the future breeding programs. In this context, apple is being increasingly considered as a model for fruit development studies, although many gaps still exist in apple research. These gaps are being filled by coupling the next generation high-throughput technologies with new physiological approaches, aimed at achieving both new basic knowledge and innovative tools to improve the final quality of the fruit. In this review, the available information on the regulatory aspects of apple fruit development will be reported and discussed in the light of the future perspectives of apple research

Auxin is part of the regulatory circuit that sustains the ripening initiation in apple fruit

The wide array of changes occurring during the ripening process of fleshy fruits can be considered as a series of events genetically determined and finely tuned by the action of a complex hormonal interplay. In climacteric fruit, such as apple, the effect of ethylene has been traditionally accounted for the ripening progression, albeit auxin, originally known as an ethylene antagonist, is now considered as an active player in the initiation of the maturation phase. To investigate the complex synergistic regulation occurring between these hormones we profiled the ethylene production and auxin accumulation in three apple cultivars that exhibit different ripening behavior, during the postharvest stage and after treatment with 1-methylcyclopropene (1-MCP), an ethylene competitor. These data were correlated with the whole transcriptome analyzed by RNA-seq, dissecting the effect of the interference acted by 1-MCP on the ethylene perception machinery. Interestingly, the ripening blockage induced an initial accumulation of auxin, highlighting the connection existing between these two hormones. This phenomenon was further supported by a candidate-gene based expression analysis that revealed an antagonistic activation of GH3 and ILL genes, encoding key steps in the regulation of the auxin homeostasis. The data we provided underline the auxin attribute to mediate the ripening initiation, through a de-novo synthesis and de-conjugation of auxin as a tentative to restore the normal ripening physiology, when ethylene metabolism is compromised at the onset of the climacteric ripenin