Phytochrome C Is A Key Factor Controlling Long-Day Flowering in Barley

The spring-type near isogenic line (NIL) of the winter-type barley ( Hordeum vulgare ssp. vulgare ) var. Hayakiso 2 (HK2) was developed by introducing VERNALIZATION-H1 ( Vrn-H1 ) for spring growth habit from the spring-type var. Indo Omugi. Contrary to expectations, the spring-type NIL flowered later than winter-type HK2. This phenotypic difference was controlled by a single gene, which cosegregated only with phytochrome C ( HvPhyC ) among three candidates around the Vrn-H1 region ( Vrn-H1 , HvPhyC , and CASEIN KINASE IIα ), indicating that HvPhyC was the most likely candidate gene. Compared with the late-flowering allele HvPhyC-l from the NIL, the early-flowering allele HvPhyC-e from HK2 had a single nucleotide polymorphism T1139C in exon 1, which caused a nonsynonymous amino acid substitution of phenylalanine at position 380 by serine in the functionally essential GAF (3′, 5′-cyclic-GMP phosphodiesterase, adenylate cyclase, formate hydrogen lyase activator protein) domain. Functional assay using a rice ( Oryza sativa ) phyA phyC double mutant line showed that both of the HvPhyC alleles are functional, but HvPhyC-e may have a hyperfunction. Expression analysis using NILs carrying HvPhyC-e and HvPhyC-l (NIL [ HvPhyC-e ] and NIL [ HvPhyC-l ], respectively) showed that HvPhyC-e up-regulated only the flowering promoter FLOWERING LOCUS T1 by bypassing the circadian clock genes and flowering integrator CONSTANS1 under a long photoperiod. Consistent with the up-regulation, NIL ( HvPhyC-e ) flowered earlier than NIL ( HvPhyC-l ) under long photoperiods. These results implied that HvPhyC is a key factor to control long-day flowering directly.