The CRYPTOCHROME 1a–ELONGATED HYPOCOTYL 5 module regulates blue light-induced salt stress tolerance in tomato

Soil salinity is one of the most harmful abiotic stresses affecting plant survival, whereas light serves as an essential environmental signal regulating plant growth and abiotic stress tolerance. Nevertheless, how light regulates plant responses to salt stress remains largely obscure. Here, we show that blue light and the photoreceptor cryptochrome 1a (CRY1a) act as pivotal positive regulators of plant responses to salt stress in tomato. Tomato seedlings exposed to blue light were more tolerant to salt stress than those exposed to darkness or red or white light. Moreover, compared to WT plants, the cry1a mutant and CRY1a-OE plants showed decreased and increased salt stress tolerance, respectively. Furthermore, blue light and salt stress induced the transcription of the key light signaling transcription factor ELONGATED HYPOCOTYL 5 (HY5) and stabilized the HY5 protein. HY5 enhanced tomato salt tolerance via the transcriptional regulation of P5CS1 and OAT to modulate proline accumulation and reduce oxidative stress. Furthermore, silencing P5CS1 and OAT impaired the salt tolerance of WT and HY5-OE plants. These findings reveal a regulatory mechanism whereby blue light signals regulate plant salt sensitivity, which will increase our understanding of how plants adapt to salt stress based on their dynamic light environment.