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. 2023 Feb;111(3):291-307.
doi: 10.1007/s11103-022-01327-z. Epub 2022 Dec 5.

A deleterious Sar1c variant in rice inhibits export of seed storage proteins from the endoplasmic reticulum

Xiuhao Bao  1 , Yongfei Wang  1 , Yanzhou Qi  2   3 , Cailin Lei  2 , Yunlong Wang  1 , Tian Pan  1 , Mingzhou Yu  1 , Yu Zhang  1 , Hongming Wu  1 , Pengcheng Zhang  1 , Yi Ji  1 , Hang Yang  1 , Xiaokang Jiang  1 , Ruonan Jing  1 , Mengyuan Yan  2 , Binglei Zhang  2 , Chuanwei Gu  1 , Jianping Zhu  1 , Yuanyuan Hao  1 , Jie Lei  1 , Shuang Zhang  2 , Xiaoli Chen  1 , Rongbo Chen  1 , Yinglun Sun  1 , Yun Zhu  2 , Xin Zhang  2 , Ling Jiang  1 , Richard G F Visser  3 , Yulong Ren  4 , Yihua Wang  5 , Jianmin Wan  1   2
Affiliations

A deleterious Sar1c variant in rice inhibits export of seed storage proteins from the endoplasmic reticulum

Xiuhao Bao et al. Plant Mol Biol. 2023 Feb.

Abstract

We identified a dosage-dependent dominant negative form of Sar1c, which confirms the essential role of COPII system in mediating ER export of storage proteins in rice endosperm. Higher plants accumlate large amounts of seed storage proteins (SSPs). However, mechanisms underlying SSP trafficking are largely unknown, especially the ER-Golgi anterograde process. Here, we showed that a rice glutelin precursor accumulation13 (gpa13) mutant exhibited floury endosperm and overaccumulated glutelin precursors, which phenocopied the reported RNAi-Sar1abc line. Molecular cloning revealed that the gpa13 allele encodes a mutated Sar1c (mSar1c) with a deletion of two conserved amino acids Pro134 and Try135. Knockdown or knockout of Sar1c alone caused no obvious phenotype, while overexpression of mSar1c resulted in seedling lethality similar to the gpa13 mutant. Transient expression experiment in tobacco combined with subcellular fractionation experiment in gpa13 demonstrated that the expression of mSar1c affects the subcellular distribution of all Sar1 isoforms and Sec23c. In addition, mSar1c failed to interact with COPII component Sec23. Conversely, mSar1c competed with Sar1a/b/d to interact with guanine nucleotide exchange factor Sec12. Together, we identified a dosage-dependent dominant negative form of Sar1c, which confirms the essential role of COPII system in mediating ER export of storage proteins in rice endosperm.

Keywords: COPII; Dominant-negative effect; Intracellular protein transport; Oryza sativa; Sar1; Seed storage protein.

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References

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