Lignin-modifying processes in the rhizosphere of arid land grasses.

Genes associated with elevated oxidative enzyme activities in arid systems have not been well characterized. To link measured oxidative activities with specific enzymes, we assembled protein-coding reads from the rhizospheres (RHZ) of two arid land grasses. Targeted gene scans for open reading frames, encoding genes potentially involved in lignin modification, resulted in 127 distinct assembly products. The putative genes included those significantly similar to Class II secretory fungal peroxidases. These genes are expressed at sufficiently high levels for assembly, annotation and differentiation across experimental conditions, and they demonstrate the interplay of root systems, environment and plant microbiomes. The genes assembled also included copper-dependent lytic polysaccharide monooxygenases. We detail the enzymes in the host grass RHZs and present a preliminary taxonomic microhabitat characterization. Our findings provide support for biologically mediated Fenton chemistry in the root zones of desert grasses, and provide insight into arid land carbon flow. These results also demonstrate a hyperdiverse microbial community. Both ribosomal RNA and messenger RNA sequences were dominated by bacteria, followed by fungal sequence abundance. Among the notable fungal sequences were those from the members of the arbuscular mycorrhizal fungi (Glomeromycota), which though abundant in this study, we rarely observed in previous PCR-based surveys.

Quantitative trait loci controlling light and hormone response in two accessions of Arabidopsis thaliana.

We have mapped quantitative trait loci (QTL) responsible for natural variation in light and hormone response between the Cape Verde Islands (Cvi) and Landsberg erecta (Ler) accessions of Arabidopsis thaliana using recombinant inbred lines (RILs). Hypocotyl length was measured in four light environments: white, blue, red, and far-red light and in the dark. In addition, white light plus gibberellin (GA) and dark plus the brassinosteroid biosynthesis inhibitor brassinazole (BRZ) were used to detect hormone effects. Twelve QTL were identified that map to loci not previously known to affect light response, as well as loci where candidate genes have been identified from known mutations. Some QTL act in all environments while others show genotype-by-environment interaction. A global threshold was established to identify a significant epistatic interaction between two loci that have few main effects of their own. LIGHT1, a major QTL, has been confirmed in a near isogenic line (NIL) and maps to a new locus with effects in all light environments. The erecta mutation can explain the effect of the HYP2 QTL in the blue, BRZ, and dark environments, but not in far-red. LIGHT2, also confirmed in an NIL, has effects in white and red light and shows interaction with GA. The phenotype and map position of LIGHT2 suggest the photoreceptor PHYB as a candidate gene. Natural variation in light and hormone response thus defines both new genes and known genes that control light response in wild accessions.