The tgd5 Mutation Affects Plastid Structure and Causes Giant Lipid Droplet Formation in Trichomes of Arabidopsis

Trichomes, epidermal protrusions in terrestrial plants, play diverse roles in plant defense, metabolism, and development. Arabidopsis thaliana, a model plant with single-celled and non-glandular trichomes, is a valuable system for studying cell differentiation in plants. However, organelle biology in Arabidopsis trichomes is relatively underexplored. Using light and transmission electron microscopy, we investigated the phenotypes of intracellular structures in Arabidopsis trichomes caused by tgd5 mutations, which are known to disrupt lipid transfer from the endoplasmic reticulum to plastids and have a large impact on chloroplast morphology in pavement and guard cells. Significant phenotypic changes in the plastid structure were observed in tgd5 trichome cells, including the absence of plastoglobuli, the emergence of clusters of electron-dense particles in the stroma, and the possibly cup-shaped morphology of plastids. Additionally, the tgd5 mutations triggered the formation of giant, up to 15 µm in diameter, neutral lipid-containing droplets in the trichome cells, as revealed using histochemical staining with lipophilic dyes. These lipid droplets were substantially larger and more frequent in trichome cells than in other types of cells in tgd5. These findings highlight the role of TGD5 in maintaining plastid structure and implicate the unique activity of lipid metabolism in Arabidopsis trichomes.