A cDNA expression library from Brassica juncea was introduced into the fission yeast Schizosaccharomyces pombe to select for transformants tolerant to cadmium. Transformants expressingOXIDATIVE STRESS 3 (OXS3) or OXS3-Like cDNA exhibited enhanced tolerance to a range of metals and oxidizing chemicals. OXS3 belongs to a family of proteins that share a highly conserved domain corresponding to a putative N-acetyltransferase or thioltransferase catalytic site. Mutations within this conserved domain abolished the ability of Arabidopsis thaliana OXS3 to enhance stress tolerance in S. pombe, indicating a role in stress tolerance for the presumptive catalytic domain. A stress-sensitive mutant of AtOXS3 and enhanced tolerance of overexpression lines support the role of OXS3 in stress tolerance. The expression of tagged B. juncea and A. thaliana OXS3 proteins in plant cells revealed a subnuclear speckling pattern related to the nucleosome in discrete parts of the chromatin. It is possible that OXS3 might act as a chromatin remodeling factor for the stress response. Signature domain of the OXS3 family at the presumptive enzymatic core:  OXS3 localizes in a speckling sub-nuclear domain with histone H4.  Legend: AtOXS3::DsRed co-transformed in onion epidermal cells with nucleolus marker fibrillarin::GFP (a), Cajal bodies marker coilin::GFP (b), spliceosome marker SC35::GFP (c), histone H4::GFP (d-e), AT-rich chromatin marker AT-hook-HMGA::GFP (g-i) and the paralog AtO3L6::GFP (j-l). (a, b) Epifluorescence microscopy, green channel without filter allowing observation of cross-excited DsRed. (c-l) Confocal microscopy: (d, g, j) green channel; (e, h, k) red channel and (c, f, i, l) merged image. Scale bars equal 20 um. |