Isolation and functional characterization of a circadian-regulated
CONSTANS homolog (GbCO) from Ginkgo biloba
Received: 23 January 2017 / Accepted: 1 June 2017 / Published online: 14 June 2017
Ó Springer-Verlag GmbH Germany 2017
Key message This is the ﬁrst report to clone and func-
tionally characterize a ﬂowering time gene GbCO in
perennial gymnosperm Ginkgo biloba. GbCO comple-
ments the co mutant of Arabidopsis, restoring normal
Abstract CONSTANS (CO) is a central regulator of pho-
toperiod pathway, which channels inputs from light, day
length, and circadian clock to promote the ﬂoral transition.
In order to understand the role of CO in gymnosperm
Ginkgo biloba, which has a long juvenile phase
(15–20 years), a CO homolog (GbCO) was isolated and
characterized from G. biloba. GbCO encodes a 1741-bp
gene with a predicted protein of 400 amino acids with two
zinc ﬁnger domains (B-box I and B-box II) and a CCT
domain. Phylogenic analysis classiﬁed GbCO into the
group 1a clade of CO families in accordance with the
grouping scheme for Arabidopsis CO (AtCO). Southern
blot analysis indicated that GbCO belongs to a multigene
family in G. biloba. Real-time PCR analysis showed that
GbCO was expressed in aerial parts of Ginkgo, with the
highest transcript level of GbCO being observed in shoot
apexes. GbCO transcript level exhibited a strong diurnal
rhythm under ﬂowering-inductive long days and peaked
during early morning, suggesting that GbCO is tightly
coupled to the ﬂoral inductive long-day signal. In addition,
an increasing trend of GbCO transcript level was observed
both in shoot tips and leaves as the shoot growth under
long-day condition, whereas GbCO transcript level
decreased in both tissues under short-day condition prior to
growth cessation of shoot in G. biloba. GbCO comple-
mented the Arabidopsis co-2 mutant, restoring normal
early ﬂowering. All the evidence being taken together, our
ﬁndings suggested that GbCO served as a potential inducer
of ﬂowering in G. biloba.
Keywords CONSTANS Á Expression Á Function analysis Á
G. biloba Á Photoperiod
Ginkgo biloba, a perennial gymnosperm, is a living fossil
from the Cenozoic Quaternary glacial period. G. biloba is a
unique and precious tree species in China and has been
widely studied given its important medicinal value (Zhou
and Zheng 2003). The main medicinal components of G.
biloba plant include terpene lactones and ﬂavonoids. These
compounds can improve blood circulation, treat cardio-
vascular diseases, and protect liver function (Goh et al.
2003). G. biloba has a long juvenile phase and spends
15–20 years in the vegetative phase before turning to
reproductive phases, which makes breeding and cultivation
of Ginkgo especially challenging. Therefore, the regulation
of ﬂowering is important from an agronomic perspective.
However, the molecular mechanisms that regulate ﬂower-
ing are still poorly understood in G. biloba.
The autonomous, photoperiod, gibberellin, vernaliza-
tion, carbohydrate, and ﬂowering inhibition pathways
Communicated by Ying-Tang Lu.
Electronic supplementary material The online version of this
article (doi:10.1007/s00299-017-2162-8) contains supplementary
material, which is available to authorized users.
& Feng Xu
College of Horticulture and Gardening, Yangtze University,
Jingzhou 434025, Hubei, China
Plant Cell Rep (2017) 36:1387–1399