Department of Plant Science, University of Manitoba, Winnipeg, R3T2N2, Canada.
Plant Physiol Biochem. 2011 Oct;49(10):1108-16. doi: 10.1016/j.plaphy.2011.06.005. Epub 2011 Jun 24.
Over the past few years non-symbiotic plant hemoglobins have been described in a variety of plant species where they fulfill several functions ranging from detoxification processes to basic aspects of plant growth and post-embryonic development. To date no information is available on the role of hemoglobins during in vitro morphogenesis. Shoot organogenesis was induced in Arabidopsis lines constitutively expressing class 1, 2 and 3 hemoglobins (GLB1, 2 and 3) and lines in which the respective genes were either downregulated by RNAi (GLB1) or knocked out (GLB2 and GLB3). The process was executed by culturing root explants on an initial auxin-rich callus induction medium (CIM) followed by a transfer onto a cytokinin-containing shoot induction medium (SIM). While the repression of GLB2 inhibited organogenesis the over-expression of GLB1 or GLB2 enhanced the number of shoots produced in culture, and altered the transcript levels of genes participating in cytokinin perception and signalling. The up-regulation of GLB1 or GLB2 activated CKI1 and AHK3, genes encoding cytokinin receptors and affected the transcript levels of cytokinin responsive regulators (ARRs). The expression of Type-A ARRs (ARR4, 5, 7, 15, and 16), feed-back repressors of the cytokinin pathway, was repressed in both hemoglobin over-expressors whereas that of several Type-B ARRs (ARR2, 12, and 13), transcription activators of cytokinin-responsive genes, was induced. Such changes enhanced the sensitivity of the root explants to cytokinin allowing the 35S::GLB1 and 35S::GLB2 lines to produce shoots at low cytokinin concentrations which did not promote organogenesis in the WT line. These results show that manipulation of hemoglobin can modify shoot organogenesis in Arabidopsis and possibly in those systems partially or completely unresponsive to applications of exogenous cytokinins.
在过去的几年中，非共生植物血红蛋白已在多种植物物种中被描述，它们在解毒过程到植物生长和胚胎后发育的基本方面等多个方面发挥作用。迄今为止，尚无有关血红蛋白在体外形态发生过程中作用的信息。通过在组成型表达第 1、2 和 3 类血红蛋白（GLB1、2 和 3）的拟南芥系和分别通过 RNAi（GLB1）下调或敲除（GLB2 和 GLB3）各自基因的系中诱导茎器官发生，来执行该过程。通过在富含初始生长素的愈伤组织诱导培养基（CIM）上培养根外植体，然后转移到含有细胞分裂素的芽诱导培养基（SIM）上来执行该过程。虽然 GLB2 的抑制抑制了器官发生，但 GLB1 或 GLB2 的过表达增强了培养物中产生的芽的数量，并改变了参与细胞分裂素感知和信号转导的基因的转录水平。GLB1 或 GLB2 的上调激活了编码细胞分裂素受体的基因 CKI1 和 AHK3，并影响了细胞分裂素响应调节剂（ARR）的转录水平。A型 ARR（ARR4、5、7、15 和 16）的表达，细胞分裂素途径的反馈抑制剂，在两种血红蛋白过表达体中均受到抑制，而几种 B 型 ARR（ARR2、12 和 13）的表达，细胞分裂素响应基因的转录激活剂，则被诱导。这种变化增强了根外植体对细胞分裂素的敏感性，使得 35S::GLB1 和 35S::GLB2 系能够在低细胞分裂素浓度下产生芽，而在 WT 系中，这些浓度不会促进器官发生。这些结果表明，血红蛋白的操纵可以改变拟南芥的茎器官发生，并且可能在那些对细胞分裂素的应用部分或完全无反应的系统中改变。
