The MADS box gene, FOREVER YOUNG FLOWER, acts as a repressor controlling floral organ senescence and abscission in Arabidopsis.

The ectopic expression of a MADS box gene FOREVER YOUNG FLOWER (FYF) caused a significant delay of senescence and a deficiency of abscission in flowers of transgenic Arabidopsis. The defect in floral abscission was found to be due to a deficiency in the timing of cell separation of the abscission zone cells. Down-regulation of INFLORESCENCE DEFICIENT IN ABSCISSION (IDA) may contribute to the delay of the floral abscission in 35S:FYF flowers. FYF was found to be highly expressed in young flowers prior to pollination and was significantly decreased after pollination, a pattern that correlated with its function. Ethylene insensitivity in senescence/abscission and the down-regulation of ETHYLENE RESPONSE DNA-BINDING FACTOR 1 (EDF1) and EDF2, downstream genes in the ethylene response, in 35S:FYF Arabidopsis suggested a role for FYF in regulating senescence/abscission by suppressing the ethylene response. This role was further supported by the fact that 35S:FYF enhanced the delay of flower senescence/abscission in ethylene response 1 (etr1), ethylene-insensitive 2 (ein2) and constitutive triple response 1 (ctr1) mutants, which have defects in upstream genes of the ethylene signaling pathway. The presence of a repressor domain in the C-terminus of FYF and the enhancement of the delay of senescence/abscission in FYF+SRDX (containing a suppression motif) transgenic plants suggested that FYF acts as a repressor. Indeed, in FYF-DR+VP16 transgenic dominant-negative mutant plants, in which FYF was converted to a potent activator by fusion to a VP16-AD motif, the senescence/abscission of the flower organs was significantly promoted, and the expression of BOP2, IDA and EDF1/2 was up-regulated. Our data suggest a role for FYF in controlling floral senescence/abscission by repressing ethylene responses and regulating the expression of BOP2 and IDA in Arabidopsis.

NAC-Like Gene GIBBERELLIN SUPPRESSING FACTOR Regulates the Gibberellin Metabolic Pathway in Response to Cold and Drought Stresses in Arabidopsis.

To investigate the functions of NAC-like genes, we reported the characterization and functional analysis of one Arabidopsis NAC-like gene which showed a novel function in the regulation of gibberellin biosynthesis and named as GIBBERELLIN SUPPRESSING FACTOR (GSF). GSF acts as a transcriptional activator and has transactivation capacity based on yeast transcription activity assays. YFP + GSF-TM (lacking a transmembrane domain) fusion proteins accumulated in the nuclei, while the YFP + GSF fusion proteins only accumulated in the ER membrane and were absent from the nuclei. These results revealed that GSF requires processing and release from the ER and transportation into the nucleus to perform its function. The ectopic expression of GSF-TM caused a dwarfism phenotype, which was correlated with the upregulation of the gibberellin (GA) deactivation genes GA2-oxidases 2/6 (GA2ox2/6) and the downregulation of the GA biosynthetic genes GA20-oxidases 1-4 (GA20ox1-4). The external application of GA rescued the dwarfism in the 35 S::GSF-TM plants, indicating that GSF affects GA biosynthesis, rather than the GA signaling pathway. Further analysis indicated that the upregulation of GA2ox2/6 is a key factor for the GSF function to regulate the GA level, since 35 S::GA20ox1 could not rescue the dwarfism in the 35 S::GSF-TM plants. Cold treatment induced the processing of the YFP + GSF fusion proteins from the ER membrane and their entry into the nuclei, which is correlated with the cold-induced upregulation of GA2oxs. In addition, the expression of GA2oxs was induced by drought, and the 35 S::GSF-TM plants showed drought tolerance compared to the wild-type plants. Our data suggest a role for GSF in response to abiotic stresses, such as cold and drought, by suppressing the biosynthesis of GA in Arabidopsis.

PeMADS6, a GLOBOSA/PISTILLATA-like gene in Phalaenopsis equestris involved in petaloid formation, and correlated with flower longevity and ovary development.

In this study, we isolated and characterized the function of a GLOBOSA/PISTILLATA-like gene, PeMADS6, from a native Phalaenopsis species, P. equestris. Southern blot analysis showed PeMADS6 as a single copy in the Phalaenopsis genome. Results of the determination of temporal and spatial expression showed that PeMADS6 was expressed and thus participated in the development of the sepals, petals, labellum and column in Phalaenopsis. Further confirmation of the expression pattern of PeMADS6 was carried out with in situ hybridization. Repressed expression of PeMADS6 in the orchid ovary was found to be pollination regulated, which suggests that the gene may have an inhibitory effect on the development of the ovary or ovule. In addition, auxin acted as the candidate signal to regulate the repression of PeMADS6 expression in the ovary. Furthermore, the flowers of transgenic Arabidopsis plants ectopically overexpressing PeMADS6 showed the morphology of petaloid sepals, with a 3- to 4-fold increase in flower longevity. Concomitantly, delayed fruit maturation was also observed in the transgenic Arabidopsis, which is consistent with the inhibitory effect of PeMADS6 on the development of the ovary. Thus, as a B-function gene, PeMADS6, not only specifies floral organ identity but has functions in flower longevity and ovary development in orchids.