Talk by Fabio Fornara from University of Milan – University of Copenhagen

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Talk by Fabio Fornara from University of Milan

On 19 June at 10.30-11.30 Fabio Fornara from the University of Milano, Italy will give a talk about "Gene Regulatory Networks Controlling Photoperiodic Flowering In Rice".

Flowering of rice (Oryza sativa) is promoted when plants are exposed to short day lengths (SDs) and repressed upon exposure to long ones (LDs). Changes in day length are perceived by regulatory molecules in the leaves that under SDs promote the production of long-distance systemic signals called florigens. After domestication, expansion of rice cultivation to higher latitudes has been accompanied by artificial selection of varieties with reduced sensitivity to day length and increased expression of the florigens, to allow flowering under non-inductive conditions.

Taking advantage of varieties cultivated in Mediterranean Europe, we are exploring the genetic variation contributing to photoperiod insensitivity and necessary to adapt rice to environments different from those of initial domestication. The analysis of novel alleles of HEADING DATE 1 (Hd1), a central regulator of rice flowering, indicates how artificial selection has operated at different levels of gene expression to impinge on photoperiod sensitivity.

The rice genome encodes at least two florigens, HEADING DATE 3a (Hd3a) and RICE FLOWERING LOCUS T 1 (RFT1), whose cognate proteins move to the shoot apical meristem (SAM) and induce extensive changes in gene expression. During this process, the SAM modifies its developmental program and forms an inflorescence called panicle. We have quantified the dynamics of global gene expression in SAMs of two rice cultivars showing distinct responses to photoperiodic induction, and identified several regulatory genes whose expression is dependent upon the photoperiod and/or florigenic proteins.

DOWNREGULATED DURING TRANSITION 1 (DDT1), a transcription factor belonging to the C2H2 zinc finger family, is strongly repressed at the meristem as soon as plants are exposed to inductive photoperiods. Transgenic rice plants in which DDT1 expression is artificially modified by distinct promoters, or gene function is abrogated through targeted editing of the locus, indicate a role for DDT1 in flower differentiation and internodes elongation. Our data suggest that DDT1 acts at the SAM to limit the vegetative-to-reproductive phase change.