Arabidopsis Vacuolar Sorting Mutants (green fluorescent seed) Can Be Identified Efficiently by Secretion of Vacuole-Targeted Green Fluorescent Protein in Their Seeds

Two Arabidopsis thaliana genes have been shown to function in vacuolar sorting of seed storage proteins: a vacuolar sorting receptor, VSR1/ATELP1, and a retromer component, MAIGO1 (MAG1)/VPS29. Here, we show an efficient and simple method for isolating vacuolar sorting mutants of Arabidopsis . The method was based on two findings in this study. First, VSR1 functioned as a sorting receptor for β-conglycinin by recognizing the vacuolar targeting signal. Second, when green fluorescent protein (GFP) fusion with the signal (GFP-CT24) was expressed in vsr1 , mag1/vps29 , and wild-type seeds, both vsr1 and mag1/vps29 gave strongly fluorescent seeds but the wild type did not, suggesting that a defect in vacuolar sorting provided fluorescent seeds by the secretion of GFP-CT24 out of the cells. We mutagenized transformant seeds expressing GFP-CT24. From ∼3,000,000 lines of M2 seeds, we obtained >100 fluorescent seeds and designated them green fluorescent seed ( gfs ) mutants. We report 10 gfs mutants, all of which caused missorting of storage proteins. We mapped gfs1 to VSR1 , gfs2 to KAM2/GRV2 , gfs10 to the At4g35870 gene encoding a novel membrane protein, and the others to different loci. This method should provide valuable insights into the complex molecular mechanisms underlying vacuolar sorting of storage proteins.