Thesis title: Mechanisms and molecular basis of the effect of natural oils on the development and resilience of plants aimed at the eco-sustainable production of vegetable species
Anthesis, defined as the moment in which flowers open and become ready for fertilization and reproduction, is a crucial trait for breeding programs and for agriculture, as it plays a critical role in various agronomic aspects, influencing processes from fertilization to plant shelf-life. Although there is considerable interest in identifying 'green' approaches to regulate anthesis, very little evidence, if any, has been presented so far. In this thesis work, we investigate whether essential oils, which are already known in the literature for their bioactive properties, can be used to regulate this process.
Working with the model species Arabidopsis thaliana and the locally relevant crop species Brassica rapa subsp. sylvestris, both belonging to the same Brassicaceae family, we propose a multi-level translational biology approach that compared phenotypic, transcriptomic and metabolic analyses to evaluate the effect of a specific family essential oil from Lavender in the regulation of the timing of anthesis.
We first optimized the concentration and timing of the treatments with essential oils from Lavandula officinalis (Lav-A) and Lavandula latifolia (Lav-B) on A. thaliana inflorescences under controlled conditions. We obtained a biologically significant delay in flower opening without damaging the plants, as also indicated by a transcriptomic analysis. Indeed, although only a few genes were altered by the treatment, key genes involved in flower development and metabolism were significantly downregulated by both Lav-A and -B. These genes were also altered upon treatment of the inflorescences with specific individual components (linalool and linalyl acetate) from the two essential oils, which also resulted in a significant delay in anthesis.
For B. rapa, field trials were conducted for two consecutive years under organic farming conditions. In the first year, treatments were applied using Lav-A, while in the second year, even Lav-B oil was included. In both years, we observed a delay in anthesis, which was further analyzed, focusing on Lav-A treatments for both years, through metabolomic profiling using nuclear magnetic resonance spectroscopy (NMR) and high-performance liquid chromatography (HPLC). Overall, NMR analysis analyses showed a general decrease in most metabolite classes related to primary metabolism. The only class of compounds that increased were glucosinolates, known for their nutraceutical importance in Brassicaceae. Consequently, we conducted targeted HPLC analyses for the main glucosinolate compounds, confirming the NMR results.
Transcriptomic analyses provided a comprehensive overview of important genes that were altered after lavender oils in both years, in particular those involved in sugar and amino acid metabolism. Notably, an upregulation of genes related to sulfur-containing compounds, including glucosinolates, was observed. We then conducted a correlation analysis between glucosinolate content and gene expression, constructing a biosynthetic pathway for glucosinolates in B. rapa and linking it to the differentially expressed genes identified through RNA-seq. This correlation analysis allowed us to identify a gene cluster containing putative transcription factors involved in the essential oil response and glucosinolate synthesis, and through this we identified four novel putative TFs.
Finally, a comparative analysis between the transcriptomes of B.rapa and A.thaliana revealed that genes related to pollen development and primary metabolism genes are co-regulated in both species.