Carabelli M, Morelli G, Whitelam G, Ruberti I
Centro di studio per gli Acide Nucleici, Dipartimento e Biologia Molecolare, Università di Roma La Sapienza P.le Aldo Moro 5, Rome, Italy.
Proc Natl Acad Sci U S A. 1996 Apr 16;93(8):3530-5. doi: 10.1073/pnas.93.8.3530.
We present evidence that a novel phytochrome (other than phytochromes A and B, PHYA and PHYB) operative in green plants regulates the "twilight-inducible" expression of a plant homeobox gene (Athb-2). Light regulation of the Athb-2 gene is unique in that it is not induced by red (R)-rich daylight or by the light-dark transition but is instead induced by changes in the ratio of R to far-red (FR) light. These changes, which normally occur at dawn and dusk (end-of-day FR), also occur during the daytime under the canopy (shade avoidance). By using pure light sources and phyA/phyB null mutants, we demonstrated that the induction of Athb-2 by changes in the R/FR ratio is mediated for the most part by a novel phytochrome operative in green plants. Furthermore, PHYB plays a negative role in repressing the accumulation of Athb-2 mRNA in the dark and a minor role in the FR response. The strict correlation of Athb-2 expression with FR-induced growth phenomena suggests a role for the Athb-2 gene in mediating cell elongation. This interpretation is supported by the finding that the Athb-2 gene is expressed at high levels in rapidly elongating etiolated seedlings. Furthermore, as either R or FR light inhibits cell elongation in etiolated tissues, they also down-regulate the expression of Athb-2 mRNA. Thus, these data support the notion that changes in light quality perceived by a novel phytochrome regulate plant development through the action of the Athb-2 homeobox gene.
我们提供的证据表明，一种在绿色植物中起作用的新型光敏色素（不同于光敏色素A和B，即PHYA和PHYB）调控着植物同源异型框基因（Athb-2）的“黄昏诱导型”表达。Athb-2基因的光调控具有独特性，它不会被富含红光（R）的日光或光暗转换所诱导，而是由R与远红光（FR）的光比例变化所诱导。这些变化通常发生在黎明和黄昏（白昼结束时的FR），在树冠下的白天（避荫反应）也会发生。通过使用纯光源和phyA/phyB缺失突变体，我们证明了R/FR比例变化对Athb-2的诱导在很大程度上是由一种在绿色植物中起作用的新型光敏色素介导的。此外，PHYB在黑暗中抑制Athb-2 mRNA积累方面起负作用，在FR反应中起次要作用。Athb-2表达与FR诱导的生长现象之间的严格相关性表明Athb-2基因在介导细胞伸长中发挥作用。这一解释得到以下发现的支持：Athb-2 gene在快速伸长的黄化幼苗中高水平表达。此外，由于R或FR光均抑制黄化组织中的细胞伸长，它们也下调Athb-2 mRNA的表达。因此，这些数据支持这样一种观点，即一种新型光敏色素所感知的光质变化通过Athb-2同源异型框基因的作用来调控植物发育。
