title: Overexpression of CONSTANS homologs CO1 and CO2 fails to alter normal reproductive onset and fall bud set in woody perennial poplar.
abstract: CONSTANS (CO) is an important flowering-time gene in the photoperiodic flowering pathway of annual Arabidopsis thaliana in which overexpression of CO induces early flowering, whereas mutations in CO cause delayed flowering. The closest homologs of CO in woody perennial poplar (Populus spp.) are CO1 and CO2. A previous report showed that the CO2/FLOWERING LOCUS T1 (FT1) regulon controls the onset of reproduction in poplar, similar to what is seen with the CO/FLOWERING LOCUS T (FT) regulon in Arabidopsis. The CO2/FT1 regulon was also reported to control fall bud set. Our long-term field observations show that overexpression of CO1 and CO2 individually or together did not alter normal reproductive onset, spring bud break, or fall dormancy in poplar, but did result in smaller trees when compared with controls. Transcripts of CO1 and CO2 were normally most abundant in the growing season and rhythmic within a day, peaking at dawn. Our manipulative experiments did not provide evidence for transcriptional regulation being affected by photoperiod, light intensity, temperature, or water stress when transcripts of CO1 and CO2 were consistently measured in the morning. A genetic network analysis using overexpressing trees, microarrays, and computation demonstrated that a majority of functionally known genes downstream of CO1 and CO2 are associated with metabolic processes, which could explain their effect on tree size. In conclusion, the function of CO1 and CO2 in poplar does not appear to overlap with that of CO from Arabidopsis, nor do our data support the involvement of CO1 and CO2 in spring bud break or fall bud set.
authors.affiliation: Department of Forestry, Mississippi State University, Mississippi State, Mississippi, United States of America.
authors.forename: Chuan-Yu
authors.initials: CY
authors.lastname: Hsu
authors.forename: Joshua P
authors.initials: JP
authors.lastname: Adams
authors.forename: Kyoungok
authors.initials: K
authors.lastname: No
authors.forename: Haiying
authors.initials: H
authors.lastname: Liang
authors.forename: Richard
authors.initials: R
authors.lastname: Meilan
authors.forename: Olga
authors.initials: O
authors.lastname: Pechanova
authors.forename: Abdelali
authors.initials: A
authors.lastname: Barakat
authors.forename: John E
authors.initials: JE
authors.lastname: Carlson
authors.forename: Grier P
authors.initials: GP
authors.lastname: Page
authors.forename: Cetin
authors.initials: C
authors.lastname: Yuceer
mesh_terms: D029681:Arabidopsis Proteins / Q000235:genetics*; D035264:Flowers / Q000235:genetics / Q000378:metabolism* / Q000502:physiology*; D018506:Gene Expression Regulation, Plant; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D030821:Plants, Genetically Modified / Q000235:genetics / Q000378:metabolism* / Q000502:physiology*; D032107:Populus / Q000235:genetics / Q000378:metabolism* / Q000502:physiology*
chemical_list: D029681:Arabidopsis Proteins; D010940:Plant Proteins