We investigated this question in two acrotonic rose cultivars (of which the buds at the end of the shoot have a greater bud break ability). We demonstrated that both the darkening of distal buds and exposure to cold (5°C) prior to transfer to mild temperatures (20°C) repress acrotony, allowing the burst of quiescent medial and proximal buds.
It has been shown that a new class of phytohormones, the strigolactones, are involved in the inhibition of axillary bud break and are produced by the MAX/RMS gene pathway (more axillary growth/ramosus). We sequenced the strigolactone pathway of MAX-homologous genes in rose and mapped them on a genetic map, revealing a co-localisation of the RwMAX2 gene and a QTL that controls the branching of a garden rose. We studied the expression of MAX rose genes in buds and internodes along the stem.
Darkening of the distal part of the shoot triggered a strong increase of RwMAX2 expression in darkened buds and bark-phloem samples, whereas it suppressed the acropetal gradient of expression of RwMAX1 observed in stems fully exposed to light. Cold treatment induced an acropetal gradient of expression of RwMAX1 in internodes and of RwMAX2 in buds along the stem. Our results suggest that the bud burst gradient along the stem cannot be explained by a gradient of expression of RwMAX genes but, instead, by their local level of expression at each individual position.

Contacts :

Laurence Hibrand-Saint Oyant et Nathalie Leduc,  IRHS unit
laurence.hibrand-saint-oyant@angers.inra.fr
nathalie.leduc@univ-angers.fr

Référence :

• Djennane S., Hibrand-Saint Oyant L., Kawamura K., Lalanne D., Laffaire M., Thouroude T., Chalain S., Sakr S., Boumaza R., Foucher F., Leduc N. (2013). Impacts of light and temperature on shoot branching gradient and expression of strigolactone synthesis and signalling genes in rose. Plant, Cell & Environment, DOI: 10.1111/pce.12191.