EARLY MATURITY 7 modifies the circadian clock and photoperiod sensitivity in barley

Breeding for variation in photoperiod response is crucial to adapt crop plants to novel 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) mutation in barley, which interacts with natural variation at PHOTOPERIOD 1 (Ppd-H1) to cause early flowering independent of the photoperiod. We identify LIGHT-REGULATED WD 1 (LWD1) as a putative candidate to underly 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 correlated with 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.