Photoperiodism‐Specific QTLs Support Switch‐Like Genetic Control of Obligate Long‐Day Photoperiodism in Mimulus guttatus

ABSTRACT

Daylength is a key environmental cue that enables plants to sense seasonal changes and regulate flowering. Although many genetic components and regulatory networks of photoperiodic flowering have been identified, current understanding is largely based on facultative long‐day and short‐day plants. Here, we investigated the genetic control of obligate long‐day photoperiodism in annual Mimulus guttatus using QTL mapping and RNA‐seq. We first identified naturally occurring facultative long‐day lines, enabling comparisons with obligate long‐day lines. By simultaneously analyzing flowering‐time and photoperiodism QTLs under the short‐day condition, we identified photoperiodism‐specific QTLs on chromosomes distinct from those associated with flowering time, supporting the existence of switch‐like genetic control of photoperiodism. In addition, photoperiodism‐specific QTLs differed among accessions, and we detected little evidence of shared transcriptional responses to daylength between facultative and obligate lines. These findings suggest that similar photoperiodic phenotypes can arise through different genetic mechanisms within M. guttatus . Overall, this study provides new insights into the genetic control of obligate long‐day photoperiodism and will help guide future research on photoperiodic regulation in plants.