Mechanistic analysis of the transition from juvenility to maturity in perennial Arabis alpina and comparison with Brassica crop species

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Many perennial plants exhibit a clearly defined juvenile phase during which they will not flower even if exposed to inductive environmental cues. We developed Arabis alpina, a member of the Brassicaceae, as a herbaceaous perennial model. In this species juvenile plants do not flower in response to vernalization, and we found that the progressive decline of miRNA156 acts as a timer defining the duration of the juvenile phase. Here we propose to deepen our knowledge of juvenility in perennials. First we will identify targets of miRNA156 that underlie this trait. In A. alpina 10 mRNAs encoding different SQUAMOSA PROMOTER BINDING LIKE PROTEIN (SPL) transcription factors are targets of miRNA156. Five of these are expressed around floral induction and orthologues of A. thaliana genes implicated in flowering. We will generate mutations that prevent miRNA156 binding to each of these 5 mRNAs and test which of the mutations reduce the juvenile phase by enabling younger plants to respond to vernalization. Secondly, we will exploit existing populations made by crossing A. alpina and A. montbretiana, an annual sister of A. alpina with no detectable juvenile phase, to genetically map and isolate loci that confer the difference in juvenility between the two species. Thirdly, we will extend our characterization of the flowering responses of A. alpina accessions collected across its European range to test for intra-species natural-genetic variation for juvenility. Fourthly, we will pursue hybrid crosses carried out between annual and perennial species in the Brassica genus and explore whether allelic variation exists in these species at loci identified in Arabis as controlling the juvenile phase. These experiments build on our earlier work in the priority programme to elucidate a major flowering trait differing between annuals and perennials and to extend the results to crops.