Overexpression of COL9, a CONSTANS‐LIKE gene, delays flowering by reducing expression of CO and FT in Arabidopsis thaliana

Abstract

Summary CONSTANS (CO) is an important floral regulator in the photoperiod pathway, integrating the circadian clock and light signal into a control for flowering time. It is known that CO promotes flowering in Arabidopsis under long-day conditions. CONSTANS-LIKE 9 (COL9) is a member of the CONSTANS-LIKE gene family, encoding a nuclear protein. The expression of COL9 is regulated by the circadian clock in the photoperiod pathway and is detected in various organs. Unexpectedly, overexpression of COL9 in transgenic Arabidopsis resulted in delayed flowering, while co-suppression lines and a transferred DNA (T-DNA) knockout line showed earlier flowering under long-day conditions. Overexpression of COL9 did not enhance the late-flowering phenotype in a co mutant background. Double overexpressors produced by overexpression of CO in COL9 transgenic lines showed an early flowering phenotype similar to single CO overexpressors. The pattern of oscillation of a number of circadian-associated genes remained unchanged in the COL9 transgenic lines. Compared with wildtype plants, the abundance of CO and FLOWERING LOCUS T (FT) mRNA was reduced in the COL9 overexpression lines. Our results indicate that COL9 is involved in regulation of flowering time by repressing the expression of CO, concomitantly reducing the expression of FT and delaying floral transition.

Association mapping reveals gene action and interactions in the determination of flowering time in barley

“…In rice, these genes are represented by Hd1 and Hd3a, respectively. In A. thaliana, the circadian clock regulated CO encodes a B-box-type zinc Wnger transcriptional activator (Putterill et al 1995), which interacts with a transcription factor complex to induce the expression of FT (Ben-Naim et al 2006;Cheng and Wang 2005;Kardailsky et al 1999;Suarez-Lopez et al 2001). While the CO gene product acts exclusively in the photoperiodic pathway (Yanovsky and Kay 2002), the FT product is involved in other Xowering pathways as well (Abe et al 2005;Ausin et al 2005;Kardailsky et al 1999;Wigge et al 2005).…”

Characterization and transgenic study of CONSTANS-LIKE8 (COL8) gene in Arabidopsis thaliana: expression of 35S:COL8 delays flowering under long-day conditions

“…Flowering time in COL9-overexpressing plants is also later than in wild-type plants under LD conditions (Cheng and Wang 2005). However, in COL9-overexpressing plants, the level of expression of CO is reduced compared with that in the wild-type (Cheng and Wang 2005), whereas in COL8-ox plants, the expression level of CO did not decrease between zt 12 and zt 16; high levels of CO at this time are important for FT activation ( Figure 5A). …”

“…As with the other members of the CO/COL family that have been analyzed to determine their subcellular localization (Cheng and Wang 2005;Datta et al 2006;Robson et al 2001), fluorescence-tagged COL8 is localized in the nucleus (Figure 2). To verify the activity of the COL8-GFP fusion protein in the COL8-GFP-ox transgenic plants, we examined the bolting time and number of rosette leaves at the time of bolting ( Figure S3).…”

“…In COL5-overexpressing plants, flowering time was earlier under SD conditions, whereas in plants with a silenced endogenous COL5, flowering time was not altered by either SD or LD conditions (Hassidim et al 2009). Overexpression of COL9 in transgenic plants resulted in delayed flowering, whereas co-suppression lines and a knockout line of COL9 showed earlier flowering under LD conditions (Cheng and Wang 2005).…”

The BBX subfamily IV

“…43 The B-box domains in the whole family are thought to mediate protein-protein interactions, but confirmation of these interactions is described only in few individuals. [44][45][46] Functional description of other members of this family have uncovered roles in circadian rhythm regulation for COL1, 47 red light photomorphogenic signaling for COL3, 48 flowering control for COL5 and COL9 49,50 and negative control of light-induced genes in the dark for BBX32. 51 Sub-family IV is composed of eight members (Fig.…”