The matrix attachment regions (MARs) associated with the Heat Shock Cognate 80 gene ( HSC80) of tomato represent specific regulatory elements.

Matrix Attachment Regions (MARs) flank certain plant genes and appear in certain cases to be necessary for their proper regulation. For example, we previously demonstrated that the MARs and introns from the Heat Shock Cognate 80 gene of tomato (HSC80) are necessary for efficient expression of HSC80-based transgenes. MARs may exert their effect by anchoring the ends of a chromatin loop to the nuclear matrix, thereby establishing an independent chromatin domain. Alternatively, MARs may facilitate interactions between activating complexes and DNA. In the first case, MARs should enhance the expression of most genes, while in the latter case, their action might be gene-specific. We addressed this problem by testing whether the HSC80 MARs affected the regulation of an unrelated transgene. We constructed a chimeric transgene composed of the Arabidopsis ADENINE PHOSPHORIBOSYLTRANSFERASE (APT) promoter fused to the maize gene Lc, which encodes a regulator of anthocyanin synthesis, and compared the expression of Lc in Arabidopsis transparent testa glabra (ttg) mutants (which lack anthocyanin pigments) transformed with transgene constructs incorporating the MARs or control DNA fragments that do not bind to the nuclear matrix. Quantitative RT-PCR analysis was used to compare Lc expression in the different transgenic lines. Whether the APT-Lc transgene was flanked by the HSC80 MARs or a control fragment had no effect on expression, while the use of a different MAR, the ARS1 MAR from yeast, significantly decreased expression (P=0.03). Comparison of single-copy and multicopy T-DNA insertions indicated that neither the HSC80 MARs nor the ARS1 MAR could protect the APT-Lc transgene from the negative effect of the integration of multiple copies. In conclusion, this work supports a model in which different regulatory elements within the HSC80 locus interact with the nuclear matrix to induce transcriptional competence.