Towards the definition of a detailed transcriptomic map of grape berry development

Abstract

Context and purpose of the study ‐ In the last years the application of genomic tools to the analysis of gene expression during grape berry development generated a huge amount of transcriptomic data from different varieties and growing conditions. This information set the stage to understand the molecular basis of crucial developmental and metabolic rearrangements occurring during grape berry formation and ripening. It is now clear that the variation of a portion of berry transcriptome is conserved across cultivars and growing conditions, and thus may be used universally to describe the stage of berry development. In this work we explore the possibility of using the transcriptomic data generated from two cultivars to define a very detailed developmental map of the grape berry.

Material and methods ‐ To map the molecular events associated with berry development at very high temporal resolution, we performed RNA‐seq analysis of berry samples collected every week from fruit‐ set to maturity from Pinot noir and Cabernet Sauvignon vines grown in the same location. The experiment was replicated across three consecutive years (2012, 2013, 2014) resulting in 219 samples overall. Applying multivariate analyses to the most variable portion of the transcriptome, we built a transcriptomic model of berry development based on the molecular information obtained from samples of both cultivars.

Results ‐ The Pinot noir and Cabernet Sauvignon samples mostly aligned in a 3D transcriptomic map (~80% of the variance described by Principal Component Analysis), allowing to define a general model of berry development based on gene expression. The performance of the model in describing the development of other grape varieties was accessed projecting RNA‐seq samples of fruit development of ten Italian cultivars onto the model. Both red and white‐skin berry samples mapped on the transcriptomic map and revealed alignment by standard ripening parameters (e.g. total soluble solids) as well as unrelated to any of these. Moreover, we validated that berry maturation of the same cultivar cultivated in different International growing regions can be well represented and aligned by means of our transcriptomic map. These results showed that the transcriptomic information can be accessed to precisely define a model of “molecular phenology” that can be used to map the ontogenetic development of the fruit with high precision and to align the stage of berry development of different grapes.