Identification and functional characterization of two bamboo FD gene homologs having contrasting effects on shoot growth and flowering

Abstract

AbstractBamboos, member of the family Poaceae, represent many interesting features with respect to their fast and extended vegetative growth, unusual, yet divergent flowering time across species, and impact of sudden, large scale flowering on forest ecology. However, not many studies have been conducted at the molecular level to characterize important genes that regulate vegetative and flowering habit in bamboo. In this study, two bambooFDgenes,BtFD1andBtFD2,which are members of the florigen activation complex (FAC) have been identified by sequence and phylogenetic analyses. Sequence comparisons identified one important amino acid, which was located in the DNA-binding basic region and was altered betweenBtFD1andBtFD2(Ala146 of BtFD1vs.Leu100 of BtFD2). Electrophoretic mobility shift assay revealed that this alteration had resulted into ten times higher binding efficiency of BtFD1 than BtFD2 to its target ACGT motif present at the promoter of theAPETALA1gene. Expression analyses in different tissues and seasons indicated the involvement ofBtFD1in flower and vegetative development, whileBtFD2was very lowly expressed throughout all the tissues and conditions studied. Finally, a tenfold increase of theAtAP1transcript level byp35S::BtFD1 Arabidopsisplants compared to wild type confirms a positively regulatory role ofBtFD1towards flowering. However, constitutive expression ofBtFD1had led to dwarfisms and apparent reduction in the length of flowering stalk and numbers of flowers/plant, whereas no visible phenotype was observed forBtFD2overexpression. This signifies that timely expression ofBtFD1may be critical to perform its programmed developmental rolein planta.