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.

Centre for Plant Genome Engineering Institute of Plant Biochemistry Heinrich Heine Universität Düsseldorf 40223 Düsseldorf Germany

Cluster of Excellence on Plant Sciences SMART Plants for Tomorrow's Needs 40223 Düsseldorf Germany

Division of Molecular Biology Centre of the Region Hana for Biotechnological and Agriculture Research Faculty of Science Palacký University CZ 779 00 Olomouc Czech

Institute of Plant Genetics Heinrich Heine Universität Düsseldorf 40223 Düsseldorf Germany

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