Expression Patterns of Key Genes in the Photoperiod and Vernalization Flowering Pathways in Lilium longiflorum with Different Bulb Sizes

Abstract

Lilium longiflorum is a wild Lilium, and its flowering transition requires a long period of cold exposure to meet the demand of vernalization. The responses of different sized bulbs to cold exposure and photoperiod are different, and the floral transition pathways of small and large bulbs are different. In this study, small and large bulbs were placed in cold storage for different weeks and then cultured at a constant ambient temperature of 25 °C under long day (LD) and short day (SD) conditions. Then, the flowering characteristics and expression patterns of key genes related to the vernalization and photoperiod pathways in different groups were calculated and analyzed. The results showed that the floral transition of Lilium longiflorum was influenced by both vernalization and photoperiod, that vernalization and LD conditions can significantly improve the flowering rate of Lilium longiflorum, and that the time from planting to visible flowering buds' appearance was decreased. The flowering time and rate of large bulbs were greatly influenced by cold exposure, and the vernalization pathway acted more actively at the floral transition stage. The floral transition of small bulbs was affected more by the photoperiod pathway. Moreover, it was speculated that cold exposure may promote greater sensitivity of the small bulbs to LD conditions. In addition, the expression of LlVRN1, LlFKF1, LlGI, LlCO5, LlCO7, LlCO16, LlFT1, LlFT3 and LlSOC1 was high during the process of floral transition, and LlCO13, LlCO14 and LlCO15 were highly expressed in the vegetative stage. The expression of LlCO13 and LlCO14 was different under different lighting conditions, and the flowering induction function of LlCO9 and LlFT3 was related to vernalization. Moreover, LlFKF1, LlGI, LlCO5, LlCO16, LlSOC1 and LlFT2 were involved in the entire growth process of plants, while LlCO6, LlCO16 and LlFT1 are involved in the differentiation and formation of small bulblets of plants after the inflorescence stage, and this process is also closely related to LD conditions. This study has great significance for understanding the molecular mechanisms of the vernalization and photoperiod flowering pathways of Lilium longiflorum.

Keywords: Lilium longiflorum; bulb size; flowering related genes; photoperiod; vernalization.

Figure 1

Effect of cold exposure and photoperiod on the flowering time and morphological characteristics of different sized bulbs of Lilium longiflorum. (A) Time from planting to visible flower bud appearance. (B) Plant height at visible bud appearance stage. (C) Number of internodes at visible bud appearance stage. (D) Average number of flowers. Notes: SD, short day (light/dark: 8/16 h); LD, long day (light/dark: 16/8 h); Small and large, bulb size; 0–9, weeks of bulb exposure to 4 °C before planting. Different lowercase letters indicate significant differences (p < 0.05).

Figure 1

Effect of cold exposure and photoperiod on the flowering time and morphological characteristics of different sized bulbs of Lilium longiflorum. (A) Time from planting to visible flower bud appearance. (B) Plant height at visible bud appearance stage. (C) Number of internodes at visible bud appearance stage. (D) Average number of flowers. Notes: SD, short day (light/dark: 8/16 h); LD, long day (light/dark: 16/8 h); Small and large, bulb size; 0–9, weeks of bulb exposure to 4 °C before planting. Different lowercase letters indicate significant differences (p < 0.05).

Figure 2

The expression patterns of LlFLC, LlFRI3, LlFRI5, LlVRN1, LlVRN2, LlSOC1 and LlFTs in scales of Lilium longiflorum before planting. Notes: Small and large meant bulb size. Relative expression levels were determined by qRT-PCR (y-axis). Data represented an average of three biological replicates with three technical replicates. Error bars represented SDEV of three biological replicates. The relative expression levels were calculated by the standard E^−ΔΔCq method.

Figure 2

The expression patterns of LlFLC, LlFRI3, LlFRI5, LlVRN1, LlVRN2, LlSOC1 and LlFTs in scales of Lilium longiflorum before planting. Notes: Small and large meant bulb size. Relative expression levels were determined by qRT-PCR (y-axis). Data represented an average of three biological replicates with three technical replicates. Error bars represented SDEV of three biological replicates. The relative expression levels were calculated by the standard E^−ΔΔCq method.

Figure 3

The expression patterns of LlSOC1, LlFTs in leaves of Lilium longiflorum grown under SD/LD conditions. Notes: These abbreviations are the same as above. SD, short day (light/dark: 8/16 h); LD, long day (light/dark: 16/8 h). * visible buds appeared time after planting.

Figure 3

The expression patterns of LlSOC1, LlFTs in leaves of Lilium longiflorum grown under SD/LD conditions. Notes: These abbreviations are the same as above. SD, short day (light/dark: 8/16 h); LD, long day (light/dark: 16/8 h). * visible buds appeared time after planting.

Figure 4

The expression patterns of LlFKF1, LlGI and LlCOLs in leaves of Lilium longiflorum grown under SD/LD conditions. Notes: These abbreviations are the same as above. * visible buds appeared time after planting.

Figure 4

The expression patterns of LlFKF1, LlGI and LlCOLs in leaves of Lilium longiflorum grown under SD/LD conditions. Notes: These abbreviations are the same as above. * visible buds appeared time after planting.

Figure 4

The expression patterns of LlFKF1, LlGI and LlCOLs in leaves of Lilium longiflorum grown under SD/LD conditions. Notes: These abbreviations are the same as above. * visible buds appeared time after planting.

Figure 5

Photoperiod related key gene network in small and large bulbs of Lilium longiflorum after planting. Notes: These abbreviations are the same as above. Arrows indicate a promoting, T-ends indicate an inhibiting interaction.