Temperature Perception Regulates Seed Germination in Solanum nigrum via Phytohormone Signaling Pathways

Black nightshade (<i>Solanum nigrum</i> L.) is a highly invasive weed in agricultural systems, primarily dispersed by seeds. Its germination is regulated by temperature, which varies among populations. We investigated the germination responses to temperature in two <i>S. nigrum</i> populations (XJ1600 and XJ1633) and identified eight putative candidate genes: <i>GA20ox1</i>, <i>GA3ox1</i>, <i>GA2ox1</i>, <i>NCED9</i>, <i>CYP707A2</i>, <i>SPT</i>, <i>PIF1</i>, and <i>ABI5</i>. These genes are involved in the phytohormone signaling pathway. Under low-temperature conditions, <i>SPT</i> likely perceives cold signals, promoting germination by up-regulating <i>GA20ox1</i> and <i>CYP707A2</i> while suppressing <i>GA2ox1</i>, thus potentially increasing bioactive GAs and reducing ABA levels. Under high-temperature conditions, <i>PIFs</i> likely perceive the heat signal. Through regulation mediated by the known negative regulator <i>SOMNUS</i> (<i>SOM</i>), <i>NCED9</i> and <i>GA2ox1</i> were up-regulated, while <i>GA3ox1</i> was down-regulated, which could collectively modulate seed germination by altering ABA and GA levels. This study clarifies how temperature regulates <i>S. nigrum</i> seed germination through integrated hormonal and genetic mechanisms. This understanding directly supports the development of predictive models for weed emergence and informs the design of sustainable control strategies.