Glucosylceramides are critical for cell‐type differentiation and organogenesis, but not for cell viability in Arabidopsis

• Published in: The Plant journal : for cell and molecular biology Vol. 84; no. 1; pp. 188 - 201
• Main Authors: Msanne, Joseph, Chen, Ming, Luttgeharm, Kyle D., Bradley, Amanda M., Mays, Elizabeth S., Paper, Janet M., Boyle, Daniel L., Cahoon, Rebecca E., Schrick, Kathrin, Cahoon, Edgar B.
• Format: Journal Article
• Language: English
• Published: England Blackwell Publishing Ltd 01.10.2015
• Subjects: Arabidopsis; Arabidopsis - cytology; Arabidopsis - growth & development; Arabidopsis - metabolism; Botany; Cell Differentiation; Cell division; Cell Survival - physiology; ceramide; differentiation; glucosylceramide; Glucosylceramide synthase; Glucosylceramides - metabolism; sphingolipids; ceramide; differentiation; Arabidopsis; Glucosylceramide synthase; sphingolipids; glucosylceramide
• ISSN: 0960-7412; 1365-313X
• DOI: 10.1111/tpj.13000

Summary Glucosylceramides (GlcCer), glucose‐conjugated sphingolipids, are major components of the endomembrane system and plasma membrane in most eukaryotic cells. Yet the quantitative significance and cellular functions of GlcCer are not well characterized in plants and other multi‐organ eukaryotes. To address this, we examined Arabidopsis lines that were lacking or deficient in GlcCer by insertional disruption or by RNA interference (RNAi) suppression of the single gene for GlcCer synthase (GCS, At2g19880), the enzyme that catalyzes GlcCer synthesis. Null mutants for GCS (designated ‘gcs‐1’) were viable as seedlings, albeit strongly reduced in size, and failed to develop beyond the seedling stage. Heterozygous plants harboring the insertion allele exhibited reduced transmission through the male gametophyte. Undifferentiated calli generated from gcs‐1 seedlings and lacking GlcCer proliferated in a manner similar to calli from wild‐type plants. However, gcs‐1 calli, in contrast to wild‐type calli, were unable to develop organs on differentiation media. Consistent with a role for GlcCer in organ‐specific cell differentiation, calli from gcs‐1 mutants formed roots and leaves on media supplemented with the glucosylated sphingosine glucopsychosine, which was readily converted to GlcCer independent of GCS. Underlying these phenotypes, gcs‐1 cells had altered Golgi morphology and fewer cisternae per Golgi apparatus relative to wild‐type cells, indicative of protein trafficking defects. Despite seedling lethality in the null mutant, GCS RNAi suppression lines with ≤2% of wild‐type GlcCer levels were viable and fertile. Collectively, these results indicate that GlcCer are essential for cell‐type differentiation and organogenesis, and plant cells produce amounts of GlcCer in excess of that required for normal development. Significance Statement Sphingolipids are essential membrane constituents in plants, but the quantities needed for various cellular functions were unknown. Here we used a null mutant in glucosylceramide synthase to show that GlcCer, a major plant sphingolipid, is not essential for basic cell division, but is required for cell differentiation and formation of organs. Notably, RNAi lines with ≤2% of wild‐type GlcCer levels form organs and are fertile, indicating that GlcCer is produced in large excess of that required for a full life cycle.