Flowering time, miRNA regulation and climatic adaptation: Variation in Brassica napus idiotypes under drought stress

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The timing of flowering is an important adaptive trait. Because flowering time and duration have a profound influence on other adaptive traits, like resistance to pests and tolerance to abiotic stresses like high/low temperatures or drought, a crosstalk is assumed between the underlying regulatory networks. While the flowering network and stress signalling pathways are well-studied, links between the two pathways still leave open questions, although important links would serve as excellent markers for abiotic stress adaptation in marker-assisted breeding programs. Micro-RNAs (miRNA) are a class of small regulatory RNAs that have been found to play an important role in numerous regulatory pathways. Associations have been established linking miRNAs with germination, flowering and senescence as well as responses to abiotic stress. They are also promising candidates as crosstalk messengers. While miRNA research is established in model plants, only minor progress has been made in determining the scope and action of miRNA-mediated trait regulation in crops. By mining genomic and transcriptome datasets we revealed miRNA binding sites in an A-genome homologues of FRIGIDA (FRI), a key floral regulator also implicated in abiotic stress adaptation. We found the corresponding copy of FRI to be upregulated in a drought-resistant B. rapa genotype under osmotic stress, whereas down-regulation was observed in drought-sensitive genotypes and in the absence of stress. Based on this potential interaction of the central flowering regulator FRI, miRNA and drought stress responses, we aim to investigate this interaction within different tissues in B. napus genotypes that exhibit differential responses to drought stress under stressed and non-stressed conditions. For this purpose, we will extract and sequence miRNA from different time points during the plant lifecycle before and after stress application. At the same time, selected Bna.FRI homologues and other potential miRNA targets will be quantified by qRT-PCR. Expression patterns will be associated to physiological influences in terms of flowering and drought response, assessed by detailed phenotyping in a large-container system which allows exact control of drought stress under conditions resembling a field soil environment.