Conserved and specific roles of photoperiod and circadian rhythm-related genes on flowering time in Lotus japonicus

Jun 18, 2026Plant science : an international journal of experimental plant biology

How day length and biological clock genes affect flowering time in Lotus japonicus

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Abstract

The evening complex (EC) acts as a master regulator of photoperiodic flowering in Lotus japonicus.

EC mutants flowered early under short-day conditions but were normal under long-day conditions.
The EC specifically suppresses flowering by directly repressing the expression of LjFTa1.
LjFTa1 is essential for flowering in L. japonicus.
Several identified genes, including LjPHYA and LjSOC1a, promote flowering specifically under long-day conditions.
The findings provide insights into the regulatory mechanisms of flowering time in legumes.

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Photoperiod and circadian rhythm play crucial roles in the control of plant flowering, and FLOWERING LOCUS T (FT) and EARLY-MATURING LOCUS 1 (E1) proteins are important in controlling flowering time in legumes. However, the regulatory mechanisms of photoperiodic flowering remain largely unknown for obligate long-day (LD) legumes such as Lotus japonicus. In this study, a series of genes involved in the circadian rhythm pathway were identified, and their expression patterns were examined in L. japonicus leaves. We show that the evening complex (EC) acts as a master regulator of photoperiodic flowering in L. japonicus. EC mutants flowered early under short-day (SD) conditions but were normal under LD, revealing its specific role in suppressing flowering under non-inductive SD. Crucially, we demonstrate that the EC inhibits flowering by directly repressing the expression of LjFTa1, but not that of LjE1Lb, defining a novel and specific regulatory node within the legume flowering network. Additionally, we found that LjFTa1 is essential for flowering. Meanwhile, LjPHYA, LjCDFa2, LjELF4L1b, LjFKF1, LjGI, LjLHY, LjPHYB, LjPRR7 and LjSOC1a promote flowering specifically under LD. Our study elucidates a key mechanism by which the EC gates photoperiodic responses and provides foundational insights into the conservation and divergence of flowering regulation in legumes.

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Conserved and specific roles of photoperiod and circadian rhythm-related genes on flowering time in Lotus japonicus

Abstract

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