Sulphur (S) is an essential element for all living organisms. The uptake, assimilation and metabolism of S in plants are well studied. However, the regulation of S homeostasis remains largely unknown. Here, we report on the identification and characterisation of the more sulphur accumulation1 (msa1-1) mutant. The MSA1 protein is localized to the nucleus and is required for both S-adenosylmethionine (SAM) production and DNA methylation. Loss of function of the nuclear localised MSA1 leads to a reduction in SAM in roots and a strong S-deficiency response even at ample S supply, causing an over-accumulation of sulphate, sulphite, cysteine and glutathione. Supplementation with SAM suppresses this high S phenotype. Furthermore, mutation of MSA1 affects genome-wide DNA methylation, including the methylation of S-deficiency responsive genes. Elevated S accumulation in msa1-1 requires the increased expression of the sulphate transporter genes SULTR1;1 and SULTR1;2 which are also differentially methylated in msa1-1. Our results suggest a novel function for MSA1 in the nucleus in regulating SAM biosynthesis and maintaining S homeostasis epigenetically via DNA methylation.
We thank Dr Hideki Takahashi in Michigan State University for providing sultr1;1 sultr1;2 double mutant, and Professor Pradipsinh Rathod in University of Washington for E. coli GS245(DE3)pLysS strain. We thank Phillip SanMiguel and the Purdue Agricultural Genomics Center for the short read sequencing and analysis. We thank Elena Yakubova and Brett Lahner for ICP-MS analysis, Dr Andrea Raab for use of the HPLC facility, and the Microscopy and Histology Core Facility at the University of Aberdeen for using the confocal laser-scanning microscopy.
This work was supported by grants from the U.S. National Science Foundation Arabidopsis 2010 Program (IOB 0419695), U.S. National Science Foundation Plant Genome Research Program (Grant IOS 0701119) and the European Commission (grant PCIG9-GA-2011-291798) to DES.