A Comprehensive Analysis of the 9-Cis Epoxy Carotenoid Dioxygenase Gene Family and Their Responses to Salt Stress in Hordeum vulgare L.

Barley (<i>Hordeum vulgare</i> L.) is among the earliest crops to be cultivated and is also considered a crucial staple crop. Nevertheless, the negative effects of abiotic stress on both the quality and productivity of barley are significant. Nine-cis-epoxycarotenoid dioxygenases (NCEDs) are rate-limiting enzymes in plants that cleave carotenoids and produce abscisic acid (ABA). The poor utilization of barley <i>NCED</i>s in stress-resistant genetic breeding is due to the lack of appropriate information about their potential function in abiotic stress. The current study revealed five <i>NCED</i> genes in the barley genome (<i>HvNCED1</i>-<i>HvNCED5</i>), which are distributed unevenly on barley chromosomes. The PF03055 domain is present in all <i>HvNCED</i>s, and they encode 413~643 amino acids. Phylogenetic analysis showed that <i>NCED</i> genes were categorized into three distinct clades, confirming the homology of <i>NCED</i> genes between <i>H. vulgare</i> L., <i>Arabidopsis thaliana</i> L., and <i>Oryza sativa</i> L. Expression analysis revealed that <i>HvNCED</i>1 is significantly upregulated under high salt stress, indicating its potential role in enhancing salt tolerance. In contrast, <i>HvNCED</i>3 and <i>HvNCED</i>4 exhibited downregulation, suggesting a complex regulatory mechanism in response to varying salt stress levels. These findings will enhance our comprehension of the genetic composition and evolutionary development of the <i>HvNCED</i> gene family and provide a basis for future research on their role in response to salt-induced stress.