Présentation de Fernando Andrès-Lalaguna, jeudi 6 mai 2021

Résumé/Description

Temperate trees are distributed over geographical regions that present wide seasonal environmental fluctuations all over the year. In order to optimize their reproductive success, temperate trees adjust their growth and flowering cycle patterns to these ever-changing conditions. This plasticity is conferred by mechanisms of environment perception (i.e. day-length and temperature) and signalling pathways that are integrated in molecular networks to modulate developmental responses. Dormancy is an essential developmental program that allows tree adaptation to low temperatures in winter. During dormancy, meristems are enclosed in protective buds and remain in a resting state until the end of the winter. After a prolonged cold period, buds reactivate their growth activity in response to the warm temperatures typical of the spring.     

The mechanisms that regulate dormancy are highly heritable, suggesting a strong genetic control of this trait. However, the genetic networks controlling dormancy cycle in trees are still unknown. In many Rosaceae species, it is believed that a group of genes encoding MADS transcription factors (TFs) is involved in the control of the dormancy cycle (i.e. from winter rest to budbreak in spring). These MADS TFs are referred as DORMANCY-ASSOCIATED MADS-BOX (DAM) and were first identified because of their genetic association with the non-dormant phenotype of the evergrowing (evg) mutant of peach (Prunus persica). DAM genes are similar to SHORT VEGETATIVE PHASE (SVP), which encodes a MADS TF that represses flowering in Arabidopsis thaliana. Although their potential role in tree phenology, the precise function and the mode of action of DAM and SVP-like genes during the dormancy cycle are still unknown. We have made use of a recently developed technology called sequential DNA Affinity Purification sequencing (seq-DAP-seq) to gain knowledge on the function of MADS TFs in the control of winter bud dormancy of apple (Malus x domestica; Md). By combining protein–protein interaction assays, seq-DAP-seq and transcriptomics, we isolated protein complexes formed between MdDAM and other dormancy related MADS TFs (MdFLC-like and MdSVP-like) and defined their transcriptional genome-wide targets. Our results show that apple DAM-, FLC- and SVP-like complexes operate in a gene regulatory network (GRN) that integrates environmental and hormonal signaling pathways to regulate dormancy cycle progression. Moreover, we are studying how the GRN controlling dormancy cycle in apple is modulated at the post-transcriptional level. To this end, we are identifying components of the GRN that undergo alternate splicing and small RNAs that potentially regulate the expression of their target genes during dormancy.

Finally, we have performed a Genome Wide Association Study (GWAS) on a core collection of apple trees to identify genes involved in the control of dormancy cycle. Our GWAS resulted in the identification of two candidate genes that are strongly associated to the budbreak time. We have determined that the polymorphisms found within the coding sequence of these genes could perturb their protein function and delay budbreak time. The potential role of these genes in affecting dormancy cycle will be discussed.