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._
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._
