Altered plastidial fatty-acid condensation is associated with changes in membrane composition and postembryonic leaf development in Arabidopsis.

Abstract

Membrane lipid composition is fundamental to organelle structure and environmental adaptation, yet how plastidial fatty acid metabolism influences developmental plasticity remains poorly understood. We examined the effects of sustained elevation of the plastidial fatty-acid enzymes KASII (β-ketoacyl-ACP synthase II) and SSI2 (Δ9 stearoyl-ACP desaturase 2) in Arabidopsis thaliana using lipidomic, ultrastructural, cellular, molecular, and physiological analyses. KASII overexpressing plants (KASIIox), but not SSI2 overexpressing plants (SSI2ox), increased carbon 18-containing lipid species and exhibited reduced plastidial galactolipids together with increased extraplastidial phospholipids. KASIIox plants displayed enlarged chloroplasts with disrupted thylakoid organization, impaired palisade differentiation, altered mesophyll patterning, and reduced seed coat mucilage. Under low light, KASIIox plants failed to exhibit the characteristic petiole elongation observed in control and SSI2ox plants, accompanied by altered phyB and PIF4 protein abundance. Exogenous gibberellin intensified, whereas inhibition of gibberellin biosynthesis partially alleviated KASIIox leaf and cellular phenotypes. Together, these findings associate sustained KASII elevation with changes in membrane lipid composition, chloroplast architecture, light-responsive growth, and postembryonic leaf development, supporting a link between plastidial fatty-acid metabolism and developmental responses to light and gibberellin availability.

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