Changes in the expression of photoperiodic bulbing genes in response to increasing daylength in long-day and short-day onion varieties

Abstract

ABSTRACT Onion bulb initiation is photoperiod-dependent. Understanding this is crucial for adapting new varieties for growth at different latitudes, as well as aiding germplasm screening for the choice of current varieties. This study aims to gain further understanding of the molecular mechanisms involved in onion bulbing process based on the parallels with well-characterised functional clock genes in the Arabidopsis flowering pathway. A comprehensive set of diurnal quantitative expression experiments was carried out to investigate the bulbing response in two different onion varieties, namely Renate, a long-day variety and Hojem, a short-day variety under increasing intermediate day-lengths. All onion homologous to Arabidopsis flowering time genes showed clear diurnal expression patterns peaking at different times of the day for both long/short-day onions, indicating their role in daylength dependent bulbing process at molecular level. Under intermediate daylengths, AcFT1 expression level increased with daylengths in both varieties, while AcFT4 was expressed in all daylengths. The two genes showed complementary expression with AcFT4 peaking in the morning and AcFT1 in the evening in longer days. The results indicate that AcFT1 and AcFT4 are negatively co-regulated, but AcFT1 is the predominant regulator of bulb formation in response to daylength.