Key Laboratory of Photosynthesis and Molecular Environmental Physiology, Institute of Botany, Chinese Academy of Sciences, Beijing, China.
PLoS One. 2009 Dec 9;4(12):e8236. doi: 10.1371/journal.pone.0008236.
Although cytokinins have been known for decades to play important roles in the regulation of plant growth and development, our knowledge of the regulatory mechanism of endogenous content of specific cytokinins remains limited.
METHODOLOGY/PRINCIPAL FINDINGS: Here, we characterized two SOB five-like (SOFL) genes, AtSOFL1 and AtSOFL2, in Arabidopsis (Arabidopsis thaliana) and showed that they acted redundantly in regulating specific cytokinin levels. Analysis of the translational fusion AtSOFL1:AtSOFL1-GUS and AtSOFL2:AtSOFL2-GUS indicated that AtSOFL1 and AtSOFL2 exhibited similar expression patterns. Both proteins were predominantly expressed in the vascular tissues of developing leaves, flowers and siliques, but barely detectable in roots and stems. Overexpression of either AtSOFL1 or AtSOFL2 led to increased cytokinin content and obvious corresponding mutant phenotypes for both transgenic seedlings and adult plants. In addition, overexpression and site-directed mutagenesis experiments demonstrated that the SOFL domains are necessary for AtSOFL2's overexpression phenotypes. Silencing or disrupting either AtSOFL1 or AtSOFL2 caused no obvious developmental defects. Endogenous cytokinin analysis, however, revealed that compared to the wild type control, the SOFL1-RNAi62 sofl2-1 double mutant accumulated lower levels of trans-zeatin riboside monophosphate (tZRMP) and N(6)-(Delta(2)-isopentenyl)adenosine monophosphate (iPRMP), which are biosynthetic intermediates of bioactive cytokinins. The double mutant also displayed decreased response to exogenous cytokinin in both callus-formation and inhibition-of-hypocotyl-elongation assays.
CONCLUSIONS/SIGNIFICANCE: Taken together, our data suggest that in plants AtSOFL1 and AtSOFL2 work redundantly as positive modulators in the fine-tuning of specific cytokinin levels as well as responsiveness.
尽管细胞分裂素数十年来一直被认为在植物生长和发育的调控中起着重要作用，但我们对特定细胞分裂素内源性含量的调控机制的了解仍然有限。
方法/主要发现：在这里，我们鉴定了拟南芥中的两个 SOB5 样（SOFL）基因 AtSOFL1 和 AtSOFL2，并表明它们在调节特定细胞分裂素水平方面具有冗余作用。AtSOFL1:AtSOFL1-GUS 和 AtSOFL2:AtSOFL2-GUS 的翻译融合分析表明，AtSOFL1 和 AtSOFL2 表现出相似的表达模式。这两种蛋白质主要在发育中的叶片、花和蒴果的维管束组织中表达，但在根和茎中几乎检测不到。过表达 AtSOFL1 或 AtSOFL2 会导致细胞分裂素含量增加，并导致两种转基因幼苗和成年植物出现明显的相应突变表型。此外，过表达和定点突变实验表明，SOFL 结构域对于 AtSOFL2 的过表达表型是必要的。沉默或破坏 AtSOFL1 或 AtSOFL2 不会导致明显的发育缺陷。然而，内源细胞分裂素分析显示，与野生型对照相比，SOFL1-RNAi62 sofl2-1 双突变体积累的反式玉米素核苷单磷酸（tZRMP）和 N（6）-（Δ2-异戊烯基）腺苷单磷酸（iPRMP）水平较低，这是生物活性细胞分裂素的生物合成中间产物。该双突变体在愈伤组织形成和抑制下胚轴伸长的测定中对外源细胞分裂素的反应也降低。
结论/意义：综上所述，我们的数据表明，在植物中，AtSOFL1 和 AtSOFL2 作为正调节剂，在精细调节特定细胞分裂素水平以及响应方面具有冗余作用。
