Tissue-specific transcriptional analysis outlines calcium-induced core metabolic changes in sweet cherry fruit.

The role of calcium in fruit ripening has been established, however knowledge regarding the molecular analysis at fruit tissue-level is still lacking. To address this, we examined the impact of foliar-applied calcium (0.5% CaCl2) in the ripening metabolism in skin and flesh tissues of the sweet cherry 'Tragana Edessis' fruit at the harvest stage. Exogenously applied calcium increased endogenous calcium level in flesh tissue and reduced fruit respiration rate and cracking traits. Fruit metabolomic along with transcriptomic analysis unraveled common and tissue-specific metabolic pathways associated with calcium feeding. Treatment with calcium diminished several alcohols (arabitol, sorbitol), sugars (fructose, maltose), acids (glyceric acid, threonic acid) and increased ribose and proline in both fruit tissues. Moreover, numerous primary metabolites, such as proline and galacturonic acid, were differentially accumulated in calcium-exposed tissues. Calcium-affected genes that involved in ubiquitin/ubl conjugation and cell wall biogenesis/degradation were differentially expressed between skin and flesh samples. Notably, skin and flesh tissues shared common calcium-responsive genes and exhibited substantial similarity in their expression patterns. In both tissues, calcium activated gene expression, most strongly those involved in plant-pathogen interaction, plant hormone signaling and MAPK signaling pathway, thus affecting related metabolic processes. By contrast, calcium depressed the expression of genes related to TCA cycle, oxidative phosphorylation, and starch/sucrose metabolism in both tissues. This work established both calcium-driven common and specialized metabolic suites in skin and flesh cherry tissues, demonstrating the utility of this approach to characterize fundamental aspects of calcium in fruit physiology.

Olive Fruit Development and Ripening: Break on through to the "-Omics" Side.

The olive tree (Olea europaea L. subsp. europaea) is the most important perennial crop in the Mediterranean region, producing table olives and oil, both appreciated for their nutraceutical value. Although olive oil quality traits have been extensively studied, much less attention has been paid to olive drupe. Olive drupe ripening is an extremely complex process involving numerous physiological and molecular changes that are unique in this fruit crop species. This review underlines the contribution of "-omics" techniques and of the recent advances in bioinformatics and analytical tools, notably next-generation sequencing and mass spectrometry, for the characterization of the olive ripening syndrome. The usage of high-dimensional datasets, such as transcriptomics, proteomics, and metabolomics, will provide a systematical description of the molecular-specific processes regulating olive fruit development and ripening. However, the incomplete sequence of the O. europaea L. reference genome has largely hampered the utilization of omics tools towards olive drupe research. Due to this disadvantage, the most reported -omics studies on fruit trees concern metabolomics and only a few transcriptomics and proteomics. In this review, up-to-date applications of -omics technologies towards olive drupe biology are addressed, and future perspectives in olive fruit research are highlighted.