Corvalán Claudia, Choe Sunghwa
School of Biological Sciences, College of Natural Sciences, Seoul National University, Seoul, 08826, South Korea.
Convergence Research Lab for Plant Functional Products, Advanced Institutes of Convergence Technology, Suwon, 16229, Gyeonggi-do, South Korea.
BMC Plant Biol. 2017 Jan 6;17(1):5. doi: 10.1186/s12870-016-0965-3.
Brassinosteroids (BRs) are steroidal phytohormones that are involved in diverse physiological processes and affect many important traits, such as plant stature, stress tolerance, leaf angle, fertility, and grain filling. BR signaling and biosynthetic pathways have been studied in various plants, such as the model dicot Arabidopsis thaliana; however, relatively little is known about these pathways in monocots.
To characterize BR-related processes in the model grass Brachypodium distachyon, we studied the response of these plants to the specific BR biosynthesis inhibitor, propiconazole (Pcz). We found that treatments with Pcz produced a dwarf phenotype in B. distachyon seedlings, similar to that observed in Pcz-treated Arabidopsis plants and in characterized BR-deficient mutants. Through bioinformatics analysis, we identified a list of putative homologs of genes known to be involved in BR biosynthesis and signaling in Arabidopsis, such as DWF4, BR6OX2, CPD, BRI1, and BIN2. Evaluating the response of these genes to Pcz treatments revealed that candidates for BdDWF4, BR6OX2 and, CPD were under feedback regulation. In addition, Arabidopsis plants heterologously expressing BdDWF4 displayed tall statures and elongated petioles, as would be expected in plants with elevated levels of BRs. Moreover, heterologous expression of BdBIN2 in Arabidopsis resulted in dwarfism, suggesting that BdBIN2 functions as a negative regulator of BR signaling. However, the dwarf phenotypes of Arabidopsis bri1-5, a weak BRI1 mutant allele, were not complemented by overexpression of BdBRI1, indicating that BdBRI1 and BRI1 are not functionally equivalent.
We identified components of the BR biosynthetic and signaling pathways in Brachypodium, and provided examples of both similarities and differences in the BR biology of these two plants. Our results suggest a framework for understanding BR biology in monocot crop plants such as Zea mays (maize) and Oryza sativa (rice).
油菜素类固醇（BRs）是甾体类植物激素，参与多种生理过程，并影响许多重要性状，如植株高度、胁迫耐受性、叶角、育性和籽粒灌浆。BR信号传导和生物合成途径已在各种植物中进行了研究，如模式双子叶植物拟南芥；然而，对于单子叶植物中这些途径的了解相对较少。
为了表征模式禾本科植物短柄草中与BR相关的过程，我们研究了这些植物对特定BR生物合成抑制剂丙环唑（Pcz）的反应。我们发现，用Pcz处理短柄草幼苗会产生矮化表型，类似于在Pcz处理的拟南芥植物和已鉴定的BR缺陷突变体中观察到的表型。通过生物信息学分析，我们鉴定了拟南芥中已知参与BR生物合成和信号传导的基因的一系列推定同源物，如DWF4、BR6OX2、CPD、BRI1和BIN2。评估这些基因对Pcz处理的反应表明，BdDWF4、BR6OX2和CPD的候选基因受到反馈调节。此外，异源表达BdDWF4的拟南芥植株表现出高大的植株和细长的叶柄，这与BR水平升高的植物预期的情况一致。此外，BdBIN2在拟南芥中的异源表达导致矮化，表明BdBIN2作为BR信号传导的负调节因子发挥作用。然而，弱BRI1突变等位基因拟南芥bri1 - 5的矮化表型并未因BdBRI1的过表达而得到互补，这表明BdBRI1和BRI1在功能上不等同。
我们鉴定了短柄草中BR生物合成和信号传导途径的成分，并提供了这两种植物BR生物学中异同的实例。我们的结果为理解单子叶作物如玉米和水稻中的BR生物学提供了一个框架。
