Hussain Anwar, Shah Syed T, Rahman Hazir, Irshad Muhammad, Iqbal Amjad
Department of Botany, University College of Science Shankar Campus, Abdul Wali Khan University Mardan, Mardan Pakistan.
Nuclear Institute for Food and Agriculture, Tarnab Peshawar Pakistan.
Front Plant Sci. 2015 Feb 5;6:46. doi: 10.3389/fpls.2015.00046. eCollection 2015.
Nostoc is widely known for its ability to fix atmospheric nitrogen and the establishment of symbiotic relationship with a wide range of plants from various taxonomic groups. Several strains of Nostoc produce phytohormones that promote growth of its plant partners. Nostoc OS-1 was therefore selected for study because of the presence of putative ipdC gene that encodes a key enzyme to produce Indole-3-acetic acid (IAA). The results indicated that both cellular and released IAA was found high with increasing incubation time and reached to a peak value (i.e., 21 pmol mg(-1)ch-a) on the third week as determined by UPLC-ESI-MS/MS. Also the Nostoc OS-1 strain efficiently colonized the roots and promoted the growth of rice as well as wheat under axenic conditions and induced ipdC gene that suggested the possible involvement of IAA in these phenotypes. To confirm the impact of IAA on root colonization efficiency and plant promoting phenotypes of Nostoc OS-1, an ipdC knockout mutant was generated by homologous recombinant method. The amount of releasing IAA, in vitro growth, root colonization, and plant promoting efficiency of the ipdC knockout mutant was observed significantly lower than wild type strain under axenic conditions. Importantly, these phenotypes were restored to wild-type levels when the ipdC knockout mutant was complemented with wild type ipdC gene. These results together suggested that ipdC and/or synthesized IAA of Nostoc OS-1 is required for its efficient root colonization and plant promoting activity.
念珠藻以其固定大气氮的能力以及与来自不同分类群的多种植物建立共生关系而广为人知。几种念珠藻菌株会产生促进其植物伙伴生长的植物激素。因此，选择念珠藻OS-1进行研究，因为它存在假定的ipdC基因，该基因编码一种产生吲哚-3-乙酸（IAA）的关键酶。结果表明，通过超高效液相色谱-电喷雾串联质谱法（UPLC-ESI-MS/MS）测定，随着培养时间的增加，细胞内和释放的IAA含量均较高，并在第三周达到峰值（即21 pmol mg(-1)叶绿素a）。此外，念珠藻OS-1菌株在无菌条件下能有效地定殖于根际，促进水稻和小麦的生长，并诱导ipdC基因表达，这表明IAA可能参与了这些表型变化。为了证实IAA对念珠藻OS-1根际定殖效率和植物促生表型的影响，通过同源重组方法构建了一个ipdC基因敲除突变体。在无菌条件下，观察到ipdC基因敲除突变体释放IAA的量、体外生长、根际定殖和植物促生效率均显著低于野生型菌株。重要的是，当ipdC基因敲除突变体用野生型ipdC基因进行互补时，这些表型恢复到了野生型水平。这些结果共同表明，念珠藻OS-1的ipdC基因和/或合成的IAA是其有效根际定殖和植物促生活性所必需的。
