The Expression Profile of Genes Related to Carotenoid Biosynthesis in Pepper Under Abiotic Stress Reveals a Positive Correlation with Plant Tolerance

In light of the increasingly adverse environmental conditions and the concomitant challenges to the survival of important crops, there is a pressing need to enhance the resilience of pepper seedlings to extreme weather. Carotenoid plays an important role in plants' resistance to abiotic stress. Nevertheless, the relationship between carotenoid biosynthesis and sweet pepper seedlings' resistance to different abiotic stresses remains uncertain. In this study, the carotenoid content in abiotic-stressed sweet pepper seedling roots was determined, revealing that carotenoid content was extremely significantly elevated by more than 16-fold under salt stress, followed by drought stress (8-fold), and slightly elevated by only about 1-fold under waterlogging stress. After that, <i>serine/threonine-protein phosphatase 2A</i> (<i>PP2A</i>) was found to be the suitable reference gene (RG) in sweet pepper seedling roots under different abiotic stresses by using RT-qPCR and RefFinder analysis. Subsequently, using <i>PP2A</i> as the RG, RT-qPCR analysis showed that the expression level of most genes associated with carotenoid biosynthesis was extremely significantly up-regulated in sweet pepper seedlings under salt and drought stress. Specifically, <i>violoxanthin deepoxidase</i> (<i>VDE</i>) was significantly up-regulated by more than 481- and 36-fold under salt and drought stress, respectively; <i>lycopene epsilon cyclase</i> (<i>LCYE</i>) was significantly up-regulated by more than 840- and 23-fold under salt and drought stress, respectively. This study contributes to a more comprehensive understanding of the carotenoid biosynthesis pathway serving as a major source of retrograde signals in pepper subjected to different abiotic stresses.