Genome-wide analysis of KCS gene family in sunflower reveals the involvement of HaKCS1-1 in wax biosynthesis and drought resistance

BACKGROUND: The β-ketoacyl-CoA synthase (KCS) family is responsible for synthesizing very-long-chain fatty acids (VLCFAs), which are precursors of cuticular waxes and plant responses to environmental stimuli. However, knowledge of this family in sunflower (Helianthus annuus L.) remain limited. RESULTS: In this study, 26 KCS family members were identified in the sunflower genome, which were unevenly distributed over 16 of the 17 chromosomes. The HaKCS proteins were divided into eight subclasses based on their phylogenetic analysis: α, β, γ, δ, ζ, ε, η, and θ. Promoter analysis indicated that HaKCS genes contain a number of cis-elements associated with stress and hormone responses. Expression profiling revealed that HaKCS genes were highly expressed in the stems, leaves and cotyledons of sunflower. Furthermore, most of HaKCS genes were up-regulated in response to exogenous abscisic acid (ABA) and drought stress. Functional study revealed that HaKCS1-1 heterologous expression in the Arabidopsis kcs1 mutant raised the accumulation of fatty acid (C20:0), alkanes (C29:0, C31:0, and C43:0), and alcohol (C26:0) in stems. It also improved drought tolerance, reduced leaf epidermal permeability, and alters the morphology of cuticular wax crystals on the stems of transgenic Arabidopsis. CONCLUSION: In summary, 26 KCS genes were identified in sunflower and exhibited stress-responsive expression patterns. HaKCS1-1 alters the crystal structure or morphology of cuticular wax, lowering epidermal permeability and increasing drought tolerance in transgenic Arabidopsis. These findings shed light on the role of KCS genes in stress adaptation and provided candidate genes for molecular enhancement of wax content in sunflower.