LUX ARRHYTHMO transcription factors regulate photoperiod-mediated resistance against common cutworm in soybean

Soybean, as a typical photoperiod-sensitive short day crop, has been studied extensively in the photoperiodic regulation of flowering time since the 1920s. Photoperiod is known to affect plant resistance to pathogens; however, whether and how insect resistance also responds to photoperiodic regulation has received much less attention. Here, we show that soybean has stronger resistance to larvae of the leaf-feeding common cutworm under short day (SD) than long day (LD) photoperiod conditions. Metabolomic analysis indicates that leaf metabolites respond to both photoperiod and simulated larval herbivory. The circadian-clock genes LUX ARRHYTHMO 1/2 (LUX1 and LUX2) primarily exert positive insect-resistance functions under inductive SD conditions, and the lux1lux2 double mutant confers no obvious difference to larval fitness under LD and SD. LUXs directly bind to regulatory regions of JASMONATE ZIM-domain (JAZ) genes JAZ1 and JAZ2, which encode repressors of jasmonate defense signaling that are genetically downstream of LUX1/2. In contrast, JAZ1 and JAZ2 work as negative regulators under the LD photoperiod, wherein their repression by LUX1/2 is weaker. Together, our study broadens the fundamental understanding of how soybean responds to photoperiod and provides a theoretical basis for insect-resistant soybean breeding.