Silicon flow from root to shoot in pepper: a comprehensive in silico analysis reveals a potential linkage between gene expression and hormone signaling that stimulates plant growth and metabolism.

Background: Silicon (Si) is categorized as a -essential element for plants thanks to the benefits on growth, development and metabolism in a hormetic manner. Si uptake is cooperatively mediated by Lsi1 and Lsi2. Nevertheless, Lsi channels have not yet been identified and characterized in pepper (), while genes involved in major physiological processes in pepper are Si-regulated. Furthermore, Si and phytohormones may act together in regulating plant growth, metabolism and tolerance against stress. Our aim was to identify potential synergies between Si and phytohormones stimulating growth and metabolism in pepper, based on in silico data.

Methods: We established a hydroponic system to test the effect of Si (0, 60, 125 and 250 mg L Si) on the concentrations of this element in different pepper plant tissues. We also performed an in silico analysis of putative genes from pepper and other species, including tomato (), potato () and , to look for -acting elements responsive to phytohormones in their promoter regions. With the Lsi1 and Lsi2 protein sequences from various plant species, we performed a phylogenetic analysis. Taking into consideration the genes retrieved from tomato, potato and , an expression profiling analysis in different plant tissues was carried out. Expression of Si-regulated genes was also analyzed in response to phytohormones and different plant tissues and developmental stages in .

Results: Si concentrations in plant tissues exhibited the following gradient: roots > stems > leaves. We were able to identify 16 and three genes in silico in the pepper genome, while putative homologs were also found in other plant species. They were mainly expressed in root tissues in the genomes analyzed. Both and Si-regulated genes displayed -acting elements responsive to diverse phytohormones. In , Si-regulated genes were transcriptionally active in most tissues analyzed, though at different expressed levels. From the set of Si-responsive genes, the gene was highly expressed in germinated seeds, whereas , and , were moderately expressed in developed flowers. All genes analyzed showed responsiveness to phytohormones and phytohormone precursors.

Conclusion: Pepper root cells are capable of absorbing Si, but small amounts of this element are transported to the upper parts of the plant. We could identify putative Si influx (Lsi1) and efflux (Lsi2) channels that potentially participate in the absorption and transport of Si, since they are mainly expressed in roots. Both and Si-regulated genes exhibit -regulatory elements in their promoter regions, which are involved in phytohormone responses, pointing to a potential connection among Si, phytohormones, plant growth, and other vital physiological processes triggered by Si in pepper.