Functional and composition differences between mitochondrial complex II in Arabidopsis and rice are correlated with the complex genetic history of the enzyme

Complex II plays a central role in mitochondrial metabolism as a component of both the electron transport chain and the tricarboxylic acid cycle. However, the composition and function of the plant enzyme has been elusive and differs from the well-characterised enzymes in mammals and bacteria. Herewith, we demonstrate that mitochondrial Complex II from Arabidopsis and rice differ significantly in several aspects: (1) Stability—Rice complex II in contrast to Arabidopsis is not stable when resolved by native electrophoresis and activity staining. (2) Composition—Arabidopsis complex II contains 8 subunits, only 7 of which have homologs in the rice genome. SDH 1 and 2 subunits display high levels of amino acid identity between two species, while the remainder of the subunits are not well conserved at a sequence level, indicating significant divergence. (3) Gene expression—the pairs of orthologous SDH1 and SDH2 subunits were universally expressed in both Arabidopsis and rice. The very divergent genes for SDH3 and SDH4 were co-expressed in both species, consistent with their functional co-ordination to form the membrane anchor. The plant-specific SDH5, 6 and 7 subunits with unknown functions appeared to be differentially expressed in both species. (4) Biochemical regulation -succinate-dependent O₂ consumption and SDH activity of isolated Arabidopsis mitochondria were substantially stimulated by ATP, but a much more minor effect of ATP was observed for the rice enzyme. The ATP activation of succinate-dependent reduction of DCPIP in frozen-thawed and digitonin-solubilised mitochondrial samples, and with or without the uncoupler CCCP, indicate that the differential ATP effect on SDH is not via the protonmotive force but likely due to an allosteric effect on the plant SDH enzyme itself, in contrast to the enzyme in other organisms.     

Mining the Cicer arietinum genome for the mildew locus O (Mlo) gene family and comparative evolutionary analysis of the Mlo genes from Medicago truncatula and some other plant species

Journal of Plant Research - The mildew locus O (Mlo) gene family is ubiquitous in land plants. Some members of this gene family are involved in negative regulation of powdery mildew resistance,...     

Attempts to characterize the mechanisms involved in the growth inhibition of Mycobacterium microti in interferon-γ or tumor necrosis factor-α activated J774A.1 cells

Abstract The growth of Mycobacterium microti was inhibited within J774A. 1 macrophage cells activated with either interferon-γ or tumor necrosis factor-α. Activation with interferon-γ or tumor necrosis factor-α alone did not stimulate the production of nitrite in J774A. 1 cells. Interferon-γ but not tumor necrosis factor-a increased the production of hydrogen peroxide in a concentration dependent manner but scavengers of reactive oxygen species did not influence the growth inhibiting effect of interferon-γ within J774A.1 cells. Both interferon-γ and tumor necrosis factor-α enhanced the fusion of M. microti containing phagosomes with lysosomes and the ultimate degradation of bacteria. Our results showed that growth inhibition of M. microti within interferon-γ or tumor necrosis factor-a stimulated J774A. 1 cells was independent of reactive oxygen intermediate and reactive nitrogen intermediate production.     

Influence of nitrogen source on photochemistry and antenna size of the photosystems in marine green macroalgae,Ulva lactuca

Photosynthesis Research - Ulva lactuca is regarded as a prospective energy crop for biorefinery owing to its affluent biochemical composition and high growth rate. In fast-growing macroalgae,...     

Effect of interleukin-1α on the growth of Mycobacterium microti within J774A.1 cells

Abstract The effect of mouse recombinant interleukin-1 α on the intracellular growth of Mycobacterium microti in a murine macrophage cell line J774A.1 was investigated. Interleukin-1 α added after infection to the M. microti -infected macrophage monolayers enhanced the growth of M. microti in a concentration-dependent manner and this growth enhancement was abrogated by neutralization of interleukin-1 α with anti-interleukin-1 α antibody. Cyclic adenosine monophosphate level in J774A.1 cells was increased by the addition of interleukin-1 α . Addition of dibutyryl cyclic adenosine monophosphate to infected J774A.1 cells increased the number of intracellular bacteria in a concentration-dependent manner. These results suggest that interleukin-1 α acts as a growth enhancer for intracellular M. microti and the growth enhancing effect of interleukin-1 α may be due to enhanced cellular cyclic adenosine monophosphate level.