1. TGD5 is required for normal morphogenesis of non‐mesophyll plastids, but not mesophyll chloroplasts, in Arabidopsis.
- Author
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Itoh, Ryuuichi D., Nakajima, Kohdai P., Sasaki, Shun, Ishikawa, Hiroki, Kazama, Yusuke, Abe, Tomoko, and Fujiwara, Makoto T.
- Subjects
PLASTIDS ,CHLOROPLASTS ,MORPHOGENESIS ,CHLOROPLAST formation ,ENDOPLASMIC reticulum ,POLLEN ,AUTOPHAGY - Abstract
Summary: Stromules are dynamic membrane‐bound tubular structures that emanate from plastids. Stromule formation is triggered in response to various stresses and during plant development, suggesting that stromules may have physiological and developmental roles in these processes. Despite the possible biological importance of stromules and their prevalence in green plants, their exact roles and formation mechanisms remain unclear. To explore these issues, we obtained Arabidopsis thaliana mutants with excess stromule formation in the leaf epidermis by microscopy‐based screening. Here, we characterized one of these mutants, stromule biogenesis altered 1 (suba1). suba1 forms plastids with severely altered morphology in a variety of non‐mesophyll tissues, such as leaf epidermis, hypocotyl epidermis, floral tissues, and pollen grains, but apparently normal leaf mesophyll chloroplasts. The suba1 mutation causes impaired chloroplast pigmentation and altered chloroplast ultrastructure in stomatal guard cells, as well as the aberrant accumulation of lipid droplets and their autophagic engulfment by the vacuole. The causal defective gene in suba1 is TRIGALACTOSYLDIACYLGLYCEROL5 (TGD5), which encodes a protein putatively involved in the endoplasmic reticulum (ER)‐to‐plastid lipid trafficking required for the ER pathway of thylakoid lipid assembly. These findings suggest that a non‐mesophyll‐specific mechanism maintains plastid morphology. The distinct mechanisms maintaining plastid morphology in mesophyll versus non‐mesophyll plastids might be attributable, at least in part, to the differential contributions of the plastidial and ER pathways of lipid metabolism between mesophyll and non‐mesophyll plastids. Significance Statement: We show that TGD5, which encodes a protein putatively involved in endoplasmic reticulum (ER)‐to‐plastid lipid trafficking, is the causal gene of suba1, an Arabidopsis stromule hyperformation mutant. Our data suggest that the regulation of stromule formation is linked to the ER pathway of plastidial glycolipid synthesis, prompting us to propose a hypothesis that partially explains the difference in stromule formation activity between mesophyll chloroplasts (relatively inactive) and non‐mesophyll plastids (generally active). [ABSTRACT FROM AUTHOR]
- Published
- 2021
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