Genome-wide identification of KCS gene family in Carya illinoinensis and their roles under abiotic stress conditions

Pecan (Carya illinoinensis) is an important economic tree species of genus Carya in the Juglandaceae. Its nuts are rich in nutrients, becoming one of the consumer's favorite ones. The pecan production is facing serious threats from drought, soil salinization and acidification. & beta;-Keto-acyl-CoA synthase (KCS) is an important enzyme responsible for the formation of very long chain fatty acid (VLCFA) and its derivatives. However, the charac-teristic of CiKCS genes family in pecan and their function under abiotic stress remain greatly unknown. Here, 30 CiKCSs were identified and distributed in the 14 chromosomes, subjected to gene duplication and strong puri-fication selection. The cis-regulatory elements in the 2 kb promoters of these CiKCSs mainly correlated with plant growth, development and stress response. Notably, CiKCS3/4/5/6/24/28 genes expressions were significantly up-regulated under drought, salt and acid stresses. Interestingly, the expression of CiKCS12 under acid stress were down-regulated. CiKCS3/5/6/12 were further shown to be mainly located in the cytoplasm, had no self-activation activity and could not interact with each other. Heterologous expression of these four genes improved VLCFA levels in tobacco and mediated the tolerance of yeast to osmotic, salt, and acid treatments. These results preliminarily suggested that CiKCS3/5/6/12 might function in the cytoplasm through monomeric forms and improve the tolerance of pecan to abiotic stress mainly by mediating VLCFA synthesis. These findings will deepen the understanding of the characteristic and function of CiKCS genes, and provide new direction and reference for the stress-resistant breeding of pecan.