Flowering time, miRNA regulation and climatic adaptation - variation in Brassica napus idiotypes under drought stress
The timing of flowering is an important adaptive trait in important crops like oilseed rape (Brassica napus) that are grown globally in highly divergent environments. Because flowering time and duration have a profound influence on other adaptive traits, for example resistance to pests and tolerance to abiotic stresses, a crosstalk is assumed between the underlying regulatory networks. While the flowering network and stress signaling pathways are well-studied, links between the two pathways still leave open questions. On the other hand, important links between flowering and stress responses can potentially serve as excellent markers for abiotic stress adaptation in marker-assisted breeding programs.
Micro-RNAs (miRNAs) 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.
Brassica napus (genome AACC) is a complex allopolyploid derived from recent hybridizations of B. rapa (AA) and B. oleracea (CC). By mining B. napus genome and transcriptome datasets we revealed miRNA binding sites in A-genome homologues of FRIGIDA (FRI), a key floral regulator also implicated in abiotic stress adaptation. We found the corresponding copy of Bra.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 are investigating this interaction throughout the plant lifecycle, under stressed and non-stressed conditions, in different tissues of winter-type B. napus genotypes that exhibit differential responses to drought stress. Besides sequencing miRNAs from different time points during, before and after stress application, selected Bna.FRI homologues and other potential miRNA targets will be quantified by qRT-PCR. Expression patterns will be associated to physiological responses, assessed by detailed phenotyping in a large-container system that allows exact control of drought stress under conditions resembling a field soil environment.
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