Phytochrome alleviates cadmium toxicity by regulating gibberellic acid and brassinolide in Nicotiana tabacum.

Soil cadmium (Cd) pollution has emerged as a substantial environmental challenge globally, hampering crop production and endangering human health. Here, we found that photoreceptor phytochromes (PHYs) were involved in regulating Cd tolerance in tobacco. Compared to wildtype (WT) plants, phytochrome-defective mutants (phyA, phyB, phyAB) displayed Cd sensitive phenotype, and had a higher reactive oxygen species (ROS) accumulation and malondialdehyde content. However, differences in Cd concentration among phyA mutants, phyB mutants, phyAB mutants, and WT plants were not observed. Consequently, the higher tolerance promoted the biomass of WT plants, thereby increasing the Cd accumulation. Furthermore, Cd stress altered the levels of gibberellin (GA) and brassinosteroid (BR), and these phytohormones were higher in WT plants. GA3 application induced the transcription of genes encoding antioxidant enzyme and suppressed the expression of genes associated with chlorophyll degradation, inhibiting chlorophyll breakdown and decreasing ROS levels in plants under Cd stress conditions. Additionally, epibrassinolide spraying promoted the expression of genes related to chlorophyll synthesis, thereby increasing chlorophyll content and maintaining plant acquisition ability. Our results suggested that phytochromes enhanced the tolerance of Nicotiana tabacum to Cd stress through regulating BR and GA.