PRFLL– a Pinus radiata homologue of FLORICAULA and LEAFY is expressed in buds containing vegetative shoot and undifferentiated male cone primordia

Abstract.

In angiosperms, the formation of the flower meristem is controlled by partially redundant flower meristem identity genes of which FLORICAULA (FLO)/LEAFY (LFY ) plays a central role. It is not known whether formation of reproductive organs of pre-angiosperm species is similarly regulated. Recently, a FLO/LFY-like cDNA, NEEDLY (NLY ), has been cloned in a conifer species Pinus radiata (D. Don). Here we report cloning of a different P inus radiata F LO/L FY-l ike cDNA, PRFLL. PRFLL had two large regions of high similarity to angiosperm FLO/LFY orthologues: amino acids 61–126 and 247–406 (50% and 81% identity, and 75% and 88% similarity, respectively, to LFY) and shorter regions of local similarity. Overall identity was 53% to LFY and 61% to NLY. Phylogenetic analysis of deduced protein sequences including partial LFY-like sequences from Pseudotsuga menziesii indicated that conifer proteins constituted a separate clade that could be divided into two groups represented by NLY and PRFLL. In contrast to angiosperms, both conifers had two paralogous proteins resembling LFY. Northern hybridisation analysis revealed expression of PRFLL in vegetative buds of juvenile, adolescent and mature trees. The transcript was not detected in vascular cambium, roots or secondary needles. To follow PRFLL expression during the early stages of cone development we analysed a temporal series of buds containing cone primordia, and developing cones, using Northern hybridisation and confocal microscopy in parallel. PRFLL mRNA was detected in buds from dominant and subordinate branches, in which cone and shoot primordia develop, and in developing male cones but not in developing female cones. Expression was particularly high in buds containing axillary primordia prior to their differentiation as male cone primordia. This is consistent with PRFLL being involved in determination of the male cone primordium identity.