Abstract
Breeding for variation in photoperiod response is crucial to adapt crop plants to various environments. Plants measure changes in day length by the circadian clock, an endogenous timekeeper that allows plants to anticipate changes in diurnal and seasonal light-dark cycles. Here, we describe the early maturity 7 (eam7) locus in barley (Hordeum vulgare), which interacts with PHOTOPERIOD 1 (Ppd-H1) to cause early flowering under non-inductive short days. We identify LIGHT-REGULATED WD 1 (LWD1) as a putative candidate to underlie the eam7 locus in barley as supported by genetic mapping and CRISPR-Cas9-generated lwd1 mutants. Mutations in eam7 cause a significant phase advance and a misregulation of core clock and clock output genes under diurnal conditions. Early flowering was linked to an upregulation of Ppd-H1 during the night and consequent induction of the florigen FLOWERING LOCUS T1 under short days. We propose that EAM7 controls photoperiodic flowering in barley by controlling the light input into the clock and diurnal expression patterns of the major photoperiod response gene Ppd-H1.