A whole-genome microarray study of Arabidopsis thaliana semisolid callus cultures exposed to microgravity and nonmicrogravity related spaceflight conditions for 5 days on board of Shenzhou 8.

The Simbox mission was the first joint space project between Germany and China in November 2011. Eleven-day-old Arabidopsis thaliana wild type semisolid callus cultures were integrated into fully automated plant cultivation containers and exposed to spaceflight conditions within the Simbox hardware on board of the spacecraft Shenzhou 8. The related ground experiment was conducted under similar conditions. The use of an in-flight centrifuge provided a 1 g gravitational field in space. The cells were metabolically quenched after 5 days via RNAlater injection. The impact on the Arabidopsis transcriptome was investigated by means of whole-genome gene expression analysis. The results show a major impact of nonmicrogravity related spaceflight conditions. Genes that were significantly altered in transcript abundance are mainly involved in protein phosphorylation and MAPK cascade-related signaling processes, as well as in the cellular defense and stress responses. In contrast to short-term effects of microgravity (seconds, minutes), this mission identified only minor changes after 5 days of microgravity. These concerned genes coding for proteins involved in the plastid-associated translation machinery, mitochondrial electron transport, and energy production.

Production of fungal and bacterial growth modulating secondary metabolites is widespread among mycorrhiza-associated streptomycetes.

BACKGROUND: Studies on mycorrhiza associated bacteria suggest that bacterial-fungal interactions play important roles during mycorrhiza formation and affect plant health. We surveyed Streptomyces Actinobacteria, known as antibiotic producers and antagonists of fungi, from Norway spruce mycorrhizas with predominantly Piloderma species as the fungal partner. RESULTS: Fifteen Streptomyces isolates exhibited substantial variation in inhibition of tested mycorrhizal and plant pathogenic fungi (Amanita muscaria, Fusarium oxysporum, Hebeloma cylindrosporum, Heterobasidion abietinum, Heterobasidion annosum, Laccaria bicolor, Piloderma croceum). The growth of the mycorrhiza-forming fungus Laccaria bicolor was stimulated by some of the streptomycetes, and Piloderma croceum was only moderately affected. Bacteria responded to the streptomycetes differently than the fungi. For instance the strain Streptomyces sp. AcM11, which inhibited most tested fungi, was less inhibitory to bacteria than other tested streptomycetes. The determined patterns of Streptomyces-microbe interactions were associated with distinct patterns of secondary metabolite production. Notably, potentially novel metabolites were produced by strains that were less antagonistic to fungi. Most of the identified metabolites were antibiotics (e.g. cycloheximide, actiphenol) and siderophores (e.g. ferulic acid, desferroxiamines). Plant disease resistance was activated by a single streptomycete strain only. CONCLUSIONS: Mycorrhiza associated streptomycetes appear to have an important role in inhibiting the growth of fungi and bacteria. Additionally, our study indicates that the Streptomyces strains, which are not general antagonists of fungi, may produce still un-described metabolites.