Characterization of late heading 1, a Heavy-Ion Beam Irradiation-Induced Mutant in Einkorn Wheat (Triticum monococcum) that Suppresses an Early-Flowering Phenotype in Plants with Deletion of PHYTOCLOCK 1

The einkorn wheat (Triticum monococcum) strain KU104-2 is an early-flowering line that was generated by X-irradiation of the einkorn wheat strain KU104-1. The early-flowering KU104-2 heads about one month earlier than KU104-1 and has a deletion of the biological-clock-component gene PHYTOCLOCK 1/LUX ARRHYTHMO (PCL1/LUX). In this study, we characterize a newly induced mutant named late-heading 1 (lh1) that was generated by heavy-ion beam irradiation of KU104-2. This new mutant shows partial suppression of the early-flowering phenotype of KU104-2. Under field conditions, lh1 plants head about one week later than KU104-2; lh1 mutants show no other significant differences in agricultural traits such as plant height, spike length, and spikelet number per spike compared with KU104-2. Analysis of plant development in a growth chamber showed that lh1 mutants exhibit a late-flowering phenotype under short-day (SD) conditions, but not under long-day (LD) conditions. This late-flowering phenotype under SD conditions is associated with the down-regulation of the flowering promoter gene VERNALIZATION 1 (VRN1) in leaves of plants at the 5th-leaf stage of growth, i.e., at the late vegetative phase. Our findings suggest that the expression level of VRN1 in the vegetative phase under short-day conditions is important for the determination of flowering time in wheat.