Résumé
To investigate the role of vacuolar sulfate in seed yield and quality, we have targeted the single pea SULTR4 gene (PsSULTR4), which encodes a transporter homologous to Arabidopsis SULTR4;1 and 4;2 that allow sulfate efflux from the vacuole to the cytosol. By simulating the 3D structure of PsSULTR4, we observed that it is similar to that of SULTR4;1 in Arabidopsis. Furthermore, a phylogenetic analysis revealed a high level of conservation of SULTR4 protein motifs across land species. A fluorescent protein fusion experiment confirmed that PsSULTR4 localizes to the vacuolar membrane.Five sultr4 mutants were identified by TILLING (Targeting Induced Local Lesions IN Genomes), two of which showed a reduced seed yield under sulfur deficiency. These mutants are currently being characterized by studying SULTR4 mRNA and protein stability, and the effect of the mutations on the simulated 3D structure. Seed yield of these two mutants was not affected under sulfur-sufficient conditions but changes in seed protein composition were observed. In particular, less sulfur-rich PA1 albumins accumulated in mature seeds. This is likely to be associated with a reduced utilization of sulfate within the seeds, since the total seed sulfur content was unchanged compared to the wild-type, whereas the seed sulfate concentration was significantly higher in both mutants. This highlights the crucial role of vacuolar sulfate in maintaining seed quality, but also seed yield when sulfur is limiting.