ABSTRACT
A MADS-box gene, designated PtAP3, was isolated from a floral bud cDNA library derived from Populus tomentosa. Analysis by multiple alignments of both nucleotide and amino acid sequences, together with phylogenetic analysis, revealed that PtAP3 is an ortholog of Arabidopsis AP3. Analysis of RNA extracts from vegetative and reproductive tissues of P. tomentosa by RT-PCR indicated that PtAP3 is expressed in roots, stems, leaves and vegetative and floral buds. Notably, the expression of PtAP3 fluctuated during floral bud development between September and February with differences between male and female buds. In the former, a gradual down-regulation during this period, interrupted by a slight up-regulation in December, was followed by a sharper up-regulation on February. In developing female floral buds, expression was stable from September to November, sharply up-regulated in December, and then gradually down-regulated until February. The functional role of PtAP3 was investigated in transgenic tobacco plants. Of 25 transformants, nine displayed an earlier flowering phenotype compared with the wild type plants. Furthermore, transgenic tobacco had faster growth and more leaves than untransformed controls. The traits proved to be heritable between the T0 and T1 generations. Our results demonstrate a regulatory role of the PtAP3 gene during plant flowering and growth and suggest that the gene may be an interesting target for genetic modification to induce early flowering in plants.
Subject(s)
Genes, Plant , Nicotiana/genetics , Populus/genetics , Amino Acid Sequence , Arabidopsis/genetics , Arabidopsis Proteins/genetics , Base Sequence , Biotechnology , DNA, Plant/genetics , Flowers/growth & development , Gene Expression Regulation, Developmental , Gene Expression Regulation, Plant , MADS Domain Proteins/chemistry , MADS Domain Proteins/genetics , Models, Molecular , Molecular Sequence Data , Phenotype , Phylogeny , Plant Leaves/growth & development , Plant Proteins/chemistry , Plant Proteins/genetics , Plants, Genetically Modified , Protein Structure, Tertiary , Seasons , Sequence Homology, Amino Acid , Nicotiana/growth & developmentABSTRACT
To understand the genetic and molecular mechanisms underlying floral development in Populus tomentosa, we isolated PtLFY, a LEAFY homolog, from a P. tomentosa floral bud cDNA library. DNA gel blot analysis showed that PtLFY is present as a single copy in the genomes of both male and female individuals of P. tomentosa. The genomic copy is composed of three exons and two introns. Relative expression levels of PtLFY in tissues of P. tomentosa were estimated by RT-PCR; our results revealed that PtLFY mRNA is highly abundant in roots and both male and female floral buds. A low level of gene expression was detected in stems and vegetative buds, and no PtLFY-specific transcripts were detected in leaves. PtLFY expression patterns were analyzed during the development of both male and female floral buds in P. tomentosa via real-time quantitative RT-PCR. Continuous, stable and high-level expression of PtLFY-specific mRNA was detected in both male and female floral buds from September 13th to February 25th, but the level of PtLFY transcripts detected in male floral buds was considerably higher than in female floral buds. Our results also showed an inverted repeat PtLFY fragment (PtLFY-IR) effectively blocked flowering of transgenic tobacco plants, and that this effect appeared to be due to post-transcriptional silencing of the endogenous tobacco LFY homologs NFL1 and NFL2.
