KNOX转录因子(TFs)主要通过对植物激素代谢的影响来调节植物发育的各个方面。特别是,KNOXTFSHOOTMERISLEMLESS激活芽顶端分生组织中细胞分裂素生物合成异戊烯基转移酶(IPT)基因。然而,迄今为止,尚未研究KNOXTFs在共生结节发育中的作用及其对结瘤过程中植物激素代谢的可能影响。细胞分裂素是众所周知的结节发育调节剂,在结节原基形成过程中起着调节细胞分裂的关键作用。最近,表明在结瘤过程中发生IPT基因的激活。因此,据推测,KNOXTF可能在结瘤时调节结节发育并激活细胞分裂素的生物合成.这项研究分析了不同KNOX基因在苜蓿中的表达。和PisumsativumL.,在两个物种中,根瘤菌接种后,KNOX3基因均上调。pKNOX3::在发育中的结节原基中观察到GUS活性。KNOX3异位表达导致在没有细菌接种的情况下在转基因根上形成结节样结构,一种与先前描述的豆科植物相似的表型,具有细胞分裂素受体的组成性激活。此外,在MtKNOX3敲低的转基因根中,发现了A型细胞分裂素反应基因的下调,以及参与细胞分裂素激活的MtIPT3和LONELYGUY2(MtLOG2)基因。一起来看,这些发现表明,KNOX3基因参与了豆科植物根瘤的共生发育,并可能在根瘤发育时调节细胞分裂素的生物合成/激活。
KNOX transcription factors (TFs) regulate different aspects of plant development essentially through their effects on phytohormone metabolism. In particular, KNOX TF SHOOTMERISTEMLESS activates the cytokinin biosynthesis ISOPENTENYL TRANSFERASE (IPT) genes in the shoot apical meristem. However, the role of KNOX TFs in symbiotic nodule development and their possible effects on phytohormone metabolism during nodulation have not been studied to date. Cytokinin is a well-known regulator of nodule development, playing the key role in the regulation of cell division during nodule primordium formation. Recently, the activation of IPT genes was shown to take place during nodulation. Therefore, it was hypothesized that KNOX TFs may regulate nodule development and activate cytokinin biosynthesis upon nodulation. This study analysed the expression of different KNOX genes in Medicago truncatula Gaertn. and Pisum sativum L. Among them, the KNOX3 gene was upregulated in response to rhizobial inoculation in both species. pKNOX3::GUS activity was observed in developing nodule primordium. KNOX3 ectopic expression caused the formation of nodule-like structures on transgenic root without bacterial inoculation, a phenotype similar to one described previously for legumes with constitutive activation of the cytokinin receptor. Furthermore, in transgenic roots with MtKNOX3 knockdown, downregulation of A-type cytokinin response genes was found, as well as the MtIPT3 and LONELYGUY2 (MtLOG2) gene being involved in cytokinin activation. Taken together, these findings suggest that KNOX3 gene is involved in symbiotic nodule development and may regulate cytokinin biosynthesis/activation upon nodule development in legume plants.