Chern M S, Eiben H G, Bustos M M
Department of Biological Sciences, UMBC 21228-5398, USA.
Plant J. 1996 Jul;10(1):135-48. doi: 10.1046/j.1365-313x.1996.10010135.x.
Expression of the MAT genes DLEC2 and PHS beta, coding for phytohemagglutinin L-subunit and beta-phaseolin, respectively, is coordinately induced in bean embryos at the onset of seed maturation and regulated at the level of transcription. Previously, it was reported that expression of DLEC2 and PHS beta genes is positively regulated by the acidic transcription activator PvALF. This article describes the regulator of MAT1 (ROM1), a basic/leucine-zipper protein that binds to hybrid G box/C box motifs found on the DLEC2 and PHS beta seed enhancers. ROM1 repressed DLEC2- and PHS beta-driven expression and antagonized transactivation of either promoter by PvALF, in a dosage-dependent manner. By contrast, a PvALF/ROM1 hybrid protein activated transcription. Both repression by ROM1 and activation by the hybrid protein required the presence of intact G-box/C-box motifs. The abundance of ROM1 mRNA in embryos was highest during the cotyledon stage and decreased rapidly at the beginning of maturation, as phytohemagglutinin and phaseolin mRNAs were induced. The results demonstrate that ROM1 is a DNA-binding site-dependent repressor and point to its possible role as a negative modulator of PvALF-activated transcription of MAT genes.
MAT基因DLEC2和PHSβ分别编码植物血凝素L亚基和β-菜豆蛋白，它们的表达在种子成熟开始时在菜豆胚中被协同诱导，并在转录水平上受到调控。此前有报道称，DLEC2和PHSβ基因的表达受酸性转录激活因子PvALF的正向调控。本文描述了MAT1的调节因子（ROM1），一种碱性/亮氨酸拉链蛋白，它能与在DLEC2和PHSβ种子增强子上发现的杂交G盒/C盒基序结合。ROM1以剂量依赖的方式抑制DLEC2和PHSβ驱动的表达，并拮抗PvALF对任何一个启动子的反式激活。相比之下，一种PvALF/ROM1杂交蛋白可激活转录。ROM1的抑制作用和杂交蛋白的激活作用都需要完整的G盒/C盒基序的存在。胚中ROM1 mRNA的丰度在子叶期最高，在成熟开始时随着植物血凝素和菜豆蛋白mRNA的诱导而迅速下降。结果表明，ROM1是一种依赖DNA结合位点的阻遏物，并指出其可能作为PvALF激活的MAT基因转录的负调节因子发挥作用。
