Ribosomal protein S6 kinase1 coordinates with TOR-Raptor2 to regulate thylakoid membrane biosynthesis in rice

Abstract

Ribosomal protein S6 kinase (S6K) functions as a key component in the target of rapamycin (TOR) pathway involved in multiple processes in eukaryotes. The role and regulation of TOR-S6K in lipid metabolism remained unknown in plants. Here we provide genetic and pharmacological evidence that TOR-Raptor2-S6K1 is important for thylakoid galactolipid biosynthesis and thylakoid grana modeling in rice (Oryza sativa L.). Genetic suppression of S6K1 caused pale yellow-green leaves, defective thylakoid grana architecture. S6K1 directly interacts with Raptor2, a core component in TOR signaling, and S6K1 activity is regulated by Raptor2 and TOR. Plants with suppressed Raptor2 expression or reduced TOR activity by inhibitors mimicked the S6K1-deficient phenotype. A significant reduction in galactolipid content was found in the s6k1, raptor2 mutant or TOR-inhibited plants, which was accompanied by decreased transcript levels of the set of genes such as lipid phosphate phosphatase α5 (LPPα5), MGDG synthase 1 (MGD1), and DGDG synthase 1 (DGD1) involved in galactolipid synthesis, compared to the control plants. Moreover, loss of LPPα5 exhibited a similar phenotype with pale yellow-green leaves. These results suggest that TOR-Raptor2-S6K1 is important for modulating thylakoid membrane lipid biosynthesis, homeostasis, thus enhancing thylakoid grana architecture and normal photosynthesis ability in rice.

Phosphatidylinositol‐hydrolyzing phospholipase C4 modulates rice response to salt and drought

“…Lipid content was referenced with deacylated anionic phospholipids used as standards. Other glycerolipids were extracted and analysed as described previously (Gao et al, ; Sun et al, ).…”

The Sulfoquinovosyltransferase-like Enzyme SQD2.2 is Involved in Flavonoid Glycosylation, Regulating Sugar Metabolism and Seed Setting in Rice

“…First-strand cDNA was produced from the RNA template by reverse transcription using the TIANscript RT Kit according to the manufacturer’s instructions (TransGen Biotech, Beijing). Quantitative real-time PCR was performed as described previously 50 . The primers for SQD2.2 were 5′-GCCGTGTTCACTGGAATGATGCAA-3′ (forward) and 5′-ATATCAGGAACACCACCAGCACGA-3′ (reverse).…”

“…The resultant lipids were separated on TLC plates using the developing solvent (acetone: toluene: H 2 O = 91:30:7.5, v/v) and were visualized with iodine vapor. The spot corresponding to SQDG was scraped out and was methylated with methanol containing 1% H 2 SO 4 and 0.05% BHT at 70 °C for 1 h. The SQDG was quantified according to the methods described previously 50 .…”

Reciprocal regulation of photosynthesis and mitochondrial respiration by TOR kinase in Chlamydomonas reinhardtii

“…Recent reports involving TOR inhibitor treatment have indicated that these effects could be due to transcriptional downregulation of genes encoding plastidic ribosomal proteins and photosynthetic proteins as well as those of the tetrapyrrole biosynthesis pathway in Arabidopsis (Dobrenel, Mancera‐Martínez, et al, ; Dong et al, ). Thus, the TORC1 complex has been shown to play a crucial role in biogenesis and maturation of chloroplast to promote leaf and cotyledon greening (Li, Gao, Xue, Wang, & Zhao, ; Li, Song, et al, ; Mohammed et al, ; Sun et al, ; Zhang et al, ). Moreover, reports have also indicated that TOR kinase plays an important role in phytohormone signaling including that of auxin, gibberellic acid, brassinosteroids, and cytokinins etc (Li & Sheen, ; Quilichini et al, ; Wang et al, ; Wu et al, ; Xiong et al, ; Zhang et al, ).…”