Effect Of Photoperiod On The Growth And Development Of Lisianthus And Functional Analysis Of Related Genes

Lisianthus is one of the most highly ranked cut flowers in international markets, and it is now enjoying increasing popularity as a pot plant in the landscape for the cultivation of dwarf varieties. The photoperiod regulation mechanism of lisianthus has been studied in this paper with the cultivar’Tiramisu’. On the one hand, we studied the photoperiod characteristics and floral transition in the aspect of cultivation, on the other hand, we explore the photoperiodic flowering mechanism from the molecular perspective.The main results of this study are as follows:1. The effects of the photoperiod on the flowering traits of Eustoma grandiflorum ’Tiramisu’(TDC) were investigated under7day-length treatments (10h/12h/14h/16h/18h/20h/24h).’Tiramisu’was deduced to be a facultative long-day plant, of which the critical day-length for flowering was14h. Plants tended to be taller and less leaf number under longer days. Compared the flowering time and flower quality in these photoperiods,14h was supposed to be the optimal photoperiod in the commercial production of lisianthus for the high flowering quality and low energy consumption.2. The flower bud differentiation process of ’Tiramisu’ was observed by paraffin method. The differentiation process lasted about3weeks and was divided into six stages:vegetative growth phase, flower initiation phase, sepal primordia phase, petal primordia phase, stamen primordia phase and pistil primordia phase. The floral transition was distinguished in the flower initiation phase, which was characterized by a distinctly raised and broadened apical meristem before appearance of sepal primordia.3. By observing the vegetative growth corresponding to flower bud differentiation phase (DP), the correlation between DP and vegetative growth traits (VGTs) was established. The results indicated that, significant linear relationships existed between each growth characteristics of ’Tiramisu’ and its flower bud differentiation phase. It could be estimated from the regression equations that the floral transition of TDC occured at21-leaf stage. Therefore, it is recommended that TDC planted under day-length of14h before21-leaf stage to promote flowering.4. Photoperiod pathway gene EgGI was isolated from lisianthus and the full gDNA and cDNA sequence was obtained with Tail-PCR method. Analysis the expression rhythms of EgGI in different photoperiods indicated that EgGI mRNA is under the control of endogenous circadian clock, and showed diurnal rhythms peaking at8-12hours later when transferred to light period, then decreased in the dark. In addition, analysis of the expression level of EgGI during floral transition in LD and SD condition indicated that, EgGI mRNA under LD condition was always significant higher than under SD condition, suggesting that EgGI possibly have involved in the process before floral transition.5. Two CO homologous genes were isolated from lisianthus and designated as EgCOL1and EgCOL2. Homologous alignment and phylogenetic tree analysis indicated that EgCOL1gene was divided to I a subclass of CO family, and the closest homologues were AtCOLl and AtCOL2; EgCOL2was divided to I c subclasses, and was most similar to AtCOL5.6. Circadian expression of EgCOLl and EgCOL2was analyzed under different photoperiods. The results indicated that EgCOLl was under the control of endogenous circadian clock; while EgCOL2had no obvious expression rhythms in four kinds of photoperiod. In addition, the transcriptional levels of EgCOLl and EgCOL2were much higher in LD condition than in SD condition, and the expression levels of the two genes both reached the peak during the floral transition period. There had more significant difference in the expression level of EgCOL1between SD and LD condition. These two genes might be involved in the process of floral transition.7. Over-expression vectors of EgCOLl and EgCOL2were constructed and transformed into tobacco. By phenotype observation, there were no differences between the tobacco transformed with EgCOLl and the wild type on flowering time and phenotype. The transgenic tobacco with EgCOL2showed a phenomenon of significant early flowering. Through expression analysis of transgenic plants, found that the plants with strong phenotype have significant higher expression levels in EgCOL2, and the expression level of NtFT and NtSOCl were also up regulated. These results suggest that EgCOL2play an important role in promoting early flowering in tobacco.