Diurnal expression of Arabidopsis Gene homologs during daylength-regulated bulb formation in onion (Allium cepa L.)

• Published in: Scientia horticulturae Vol. 261; p. 108946
• Main Authors: Rashid, Md. Harun Ar, Thomas, Brian
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 05-02-2020
• Subjects: AcCOL; AcFKF1; AcFT; AcGI; Circadian clock genes; RNA-seq; SD; RNA-seq; LD; Circadian clock genes; AcGI; AcFKF1; AcCOL; AcFT
• ISSN: 0304-4238; 1879-1018
• DOI: 10.1016/j.scienta.2019.108946

•The paper provides new insights into the molecular basis for diurnal regulation of bulbing in onion.•Homologs of Arabidopsis photoperiodic flowering genes show similar diurnal expression in onion.•AcFt1, a bulb promoter and AcFt4, an inhibitor are expressed at different times of the day•Two new members of the onion CONSTANS are identified, including a candidate daylength regulator.
Bulb initiation in long-day onion is regulated at the physiological level in a similar way to the photoperiodic regulation of flowering in Arabidopsis. This study establishes in onion, the diurnal time-course expression, in onion, of key genes particularly linked to circadian regulation in Arabidopsis. The long-day onion variety ‘Renate’ and the short-day (SD) onion variety ‘Hojem’ were used for these experiments. Onion plants were grown under natural LD conditions in the Phytobiology Glasshouse and immediately after bulbing they were transferred to two SANYO 2279 controlled environment cabinets for 10 d providing constant LD (16 h photoperiod including 8 h fluorescent followed by 8 h incandescent light) and constant short days (8 h photoperiod with fluorescent light). Five FLOWERING LOCUS T (FT) and three CONSTANS-LIKE (COL) genes were identified in onion, including two novel COL sequences through RNA-Seq analysis. The new AcCOL2 shows a diurnal pattern of expression similar to Arabidopsis CONSTANS (CO). Allium cepa FLAVIN-BINDING, KELCH REPEAT, F-BOX PROTEIN 1 (AcFKF1), Allium cepa GIGANTEA (AcGI) and AcCOL2 showed good diurnal expression patterns consistent with photoperiod sensing and regulation of AcFT1. All FT genes exhibited different diurnal expression patterns peaking at different times of the day. Notably, AcFT1 was expressed in the later part of the day which is very similar to the expression of Arabidopsis FT, while AcFT4 was expressed late in the night and the early morning in both Renate and Hojem varieties of onion, with the caveat that, AcFT4 is under less stringent daylength control in Hojem than in Renate. The timing of the peaks and expression pattern in both Renate F1 and Hojem suggest that AcFT5 may be under circadian or diurnal regulation under LD conditions and AcFT6 might not be circadian or diurnally regulated. These findings will help to understand the basis of the difference between responses of onions adapted to different latitudes, which is important for developing new varieties.