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Cellular Microbiology
16, No. 1, 2014; Pages: 2738

Commensals, probiotics and pathogens in the Caenorhabditis elegansmodel

Gregor Langen, Sabrina von Einem, Aline Koch, Jafargholi Imani, Subhash B Pai1, Murli Manohar, Katrin Ehlers, Hyong Woo Choi, Martina Claar, Rebekka Schmidt, Hyung-Gon Mang, Yogendra Bordiya, Hong-Gu Kang, Daniel F. Klessig and Karl-Heinz Kogel

Research centre for Biosystems, Land use and Nutrition, Justus-Liebig-University.


MORC1 and MORC2, two of the seven members of the Arabidopsis thaliana CRT1 (compromised recognition of TCV) subfamily of microrchidia (MORC) GHKL ATPases, were previously shown to be required in multiple layers of plant immunity. Here we show that the Hordeum vulgare MORCs also are involved in disease resistance. Genome-wide analyses identified five MORCs that are 37-48% identical on the protein level to AtMORC1. Unexpectedly, and in clear contrast to Arabidopsis, RNA interference-mediated knock-down (KD) of MORC in barley resulted in enhanced basal resistance and effector-triggered, MLA12-mediated resistance against the biotrophic powdery mildew fungus (Blumeria graminis f.sp. hordei), while MORC overexpression decreased resistance. Moreover, barley KD mutants also showed higher resistance to Fusarium graminearum. Barley MORCs, like their Arabidopsis homologs, contain the highly conserved GHKL ATPase and S5 domains, which identify them as members of the MORC superfamily. Like AtMORC1, barley MORC1 (HvMORC1) binds DNA and has Mn2+-dependent endonuclease activities, suggesting that the contrasting function of MORC1 homologs in barley vs. Arabidopsis is not due to differences in their enzyme activities. In contrast to AtMORCs, which are involved in silencing of transposons that are largely restricted to pericentromeric regions, barley MORC mutants did not show a loss of transposon gene silencing regardless of their genomic location. Reciprocal overexpression of MORC1 homologs in barley and Arabidopsis showed that AtMORC1 and HvMORC1 could not restore each other's function. Together these results suggest that MORC proteins function as modulators of immunity, which can act negatively (barley) or positively (Arabidopsis) dependent on the species.

Keywords: Arabidopsis thaliana CRT1; subfamily of microrchidia; Arabidopsis; homologs.

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