The KCS gene is involved in the formation of chloroplast stromules and other physiological processes in jute (Corchorus capsularis L.)

•Over-expressing 3-ketoacyl-CoA synthase gene increased the stromules frequency and lignin content.•The stem bark thickness, stem diameter and plant height was increased in 3-ketoacyl-CoA synthase gene over-expressing plants.•The chloroplast stromules, lignin content and stem diameter was reduced in 3-ketoacyl-CoA synthase gene edited plants.•Over-expressing 3-ketoacyl-CoA synthase gene could increased drought tolerance under 29% polyethylene glycol 6000 stress. Drought is one of the most serious abiotic factors restricting the growth and development of jute. Stromules are highly dynamic tubular protuberances on the surface of the plastid that play an important role in the responses to biotic and abiotic stresses, as well as in signal transduction between different plastids and between plastids and the nucleus in plants. However, the mechanism underlying the formation of stromules remains unclear. In this study, chloroplast-labeled jute was utilized to clone the jute 3-ketoacyl-CoA synthase (KCS) gene and obtain its genomic and cDNA sequences. KCS gene expression peaks after 6 h of drought stress. Subsequently, overexpression and gene editing vectors of the jute KCS gene were constructed and transfected into the callus of jute via transformation mediated by Agrobacterium tumefaciens. The transformed plants were identified by sequencing, q-PCR and Southern blot. In addition, the chloroplast stromules of the transformed plants were observed by confocal microscopy. In comparison with control plants, plants overexpressing KCS gene displayed a significantly increased chloroplast stromules frequency of mesophyll cells, enhanced lignin content, and increased growth rate, stem bark thickness, stem diameter and plant height. In addition, KCS expression was significantly increased drought tolerance under 29% polyethylene glycol 6000 (PEG6000) stress. However, in plants with an edited version of the KCS gene, the chloroplast stromules, lignin content and stem diameter was reduced. These results indicate that the jute KCS gene is involved in other processes related to jute growth and development in addition to the formation of chloroplast stromules.