Ku Amy Tsu, Huang Yi-Shiuan, Wang Yu-Shu, Ma Daifu, Yeh Kai-Wun
Institute of Plant Biology, National Taiwan University, 10617, Taipei, Taiwan.
Ann Bot. 2008 Jul;102(1):57-67. doi: 10.1093/aob/mcn067. Epub 2008 May 7.
The tuberization mechanism of sweet potato (Ipomoea batatas) has long been studied using various approaches. Morphological data have revealed that the tuberizing events result from the activation of the cambium, followed by cell proliferation. However, uncertainties still remain regarding the regulators participating in this signal-transduction pathway. An attempt was made to characterize the role of one MADS-box transcription factor, which was preferentially expressed in sweet potato roots at the early tuberization stage.
A differential expression level of IbMADS1 (Ipomoea batatas MADS-box 1) was detected temporally and spatially in sweet potato tissues. IbMADS1 responses to tuberization-related hormones were assessed. In order to identify the evolutionary significance, the expression pattern of IbMADS1 was surveyed in two tuber-deficient Ipomoea relatives, I. leucantha and I. trifida, and compared with sweet potato. In functional analyses, potato (Solanum tuberosum) was employed as a heterologous model. The resulting tuber morphogenesis was examined anatomically in order to address the physiological function of IbMADS1, which should act similarly in sweet potato.
IbMADS1 was preferentially expressed as tuberous root development proceeded. Its expression was inducible by tuberization-related hormones, such as jasmonic acid and cytokinins. In situ hybridization data showed that IbMADS1 transcripts were specifically distributed around immature meristematic cells within the stele and lateral root primordia. Inter-species examination indicated that IbMADS1 expression was relatively active in sweet potato roots, but undetectable in tuber-deficient Ipomoea species. IbMADS1-transformed potatoes exhibited tuber morphogenesis in the fibrous roots. The partial swellings along fibrous roots were mainly due to anomalous proliferation and differentiation in the xylem.
Based on this study, it is proposed that IbMADS1 is an important integrator at the initiation of tuberization. As a result, the initiation and development of tuberous roots seems to be well regulated by a network involving a MADS-box gene in which such hormones as jasmonic acid and cytokinins may act as trigger factors.
长期以来，人们一直采用各种方法研究甘薯（Ipomoea batatas）的块茎形成机制。形态学数据表明，块茎形成事件源于形成层的激活，随后是细胞增殖。然而，参与这一信号转导途径的调控因子仍存在不确定性。本研究旨在表征一种MADS盒转录因子的作用，该转录因子在甘薯块茎形成早期的根中优先表达。
检测了IbMADS1（甘薯MADS盒1）在甘薯组织中的时空差异表达水平。评估了IbMADS1对块茎形成相关激素的反应。为了确定其进化意义，在两种缺乏块茎的甘薯近缘种白花甘薯（I. leucantha）和三裂叶甘薯（I. trifida）中检测了IbMADS1的表达模式，并与甘薯进行比较。在功能分析中，以马铃薯（Solanum tuberosum）作为异源模型。通过解剖学检查所得的块茎形态发生，以阐明IbMADS1在甘薯中可能发挥类似作用的生理功能。
随着块根的发育，IbMADS1优先表达。其表达可被茉莉酸和细胞分裂素等块茎形成相关激素诱导。原位杂交数据显示，IbMADS1转录本特异性分布于中柱内未成熟的分生细胞和侧根原基周围。种间检测表明，IbMADS1在甘薯根中的表达相对活跃，但在缺乏块茎的甘薯近缘种中未检测到。转IbMADS1基因的马铃薯在纤维根中表现出块茎形态发生。纤维根上的部分肿胀主要是由于木质部的异常增殖和分化。
基于本研究，推测IbMADS1是块茎形成起始阶段的重要整合因子。因此，块根的起始和发育似乎受到一个涉及MADS盒基因的网络的良好调控，其中茉莉酸和细胞分裂素等激素可能作为触发因子。
