Schäffner A R, Sheen J
Genetics Department, Harvard Medical School, Massachusetts General Hospital, Boston 02114.
Plant Cell. 1991 Sep;3(9):997-1012. doi: 10.1105/tpc.3.9.997.
Although the molecular mechanisms of dicot photosynthetic gene regulation have been pursued actively, comparable studies of monocot regulation have been slow to come forth. We show here that monocot (maize and wheat) but not dicot (pea, tobacco, and Arabidopsis) ribulose-1,5-bisphosphate carboxylase small subunit (rbcS) gene promoters are active in maize mesophyll protoplasts. The evolutionarily conserved GT and G boxes of dicot rbcS promoters are not essential for light-responsive expression in monocot leaf cells. Instead, at least six constitutive and light-sensitive regulatory elements are likely important for maize rbcS expression. Synergism between upstream and downstream promoter elements is required. Whereas in dicots, light triggers coupled leaf development and photosynthetic gene expression, in monocots, light regulation of rbcS is uncoupled from leaf development. Light regulation of maize rbcS may be divided into direct and indirect contributions mediated by different regulatory elements. Because wheat and maize rbcS promoters show sequence homologies and similar expression patterns in monocot and dicot leaf cells, it appears likely that monocots share conserved regulatory elements irrespective of whether they utilize the C3 or C4 pathway for carbon fixation.
尽管对双子叶植物光合基因调控的分子机制已进行了积极探索，但对单子叶植物调控的类似研究却进展缓慢。我们在此表明，单子叶植物（玉米和小麦）而非双子叶植物（豌豆、烟草和拟南芥）的1,5-二磷酸核酮糖羧化酶小亚基（rbcS）基因启动子在玉米叶肉原生质体中具有活性。双子叶植物rbcS启动子中进化保守的GT盒和G盒对于单子叶植物叶细胞中的光响应表达并非必需。相反，至少六个组成型和光敏感调控元件可能对玉米rbcS表达很重要。上游和下游启动子元件之间需要协同作用。在双子叶植物中，光触发叶片发育和光合基因表达的耦合，而在单子叶植物中，rbcS的光调控与叶片发育解耦。玉米rbcS的光调控可分为由不同调控元件介导的直接和间接作用。由于小麦和玉米rbcS启动子在单子叶和双子叶植物叶细胞中显示出序列同源性和相似的表达模式，无论单子叶植物是利用C3还是C4途径进行碳固定，它们似乎都共享保守的调控元件。
