Gene expression response of Medicago truncatula roots treated with symbiotic lipochitooligosaccharides (LCOs)

Legumes interact with soil microbes, leading to the development of nitrogen-fixing root nodules and arbuscular mycorrhizal (AM) roots. While nodule initiation by diffusible lipochitooligosaccharide (LCO) Nod-factors of bacterial origin (Nod-LCOs) is well characterized, diffusible AM fungal signals were only recently identified as sulphated and non-sulphated LCOs (sMyc-LCOs and nsMyc-LCOs). Applying Myc-LCOs in parallel to Nod-LCOs, we used GeneChips to detail the global programme of gene expression in response to the external application of symbiotic LCOs. To harvest tissues for transcriptome profiling, three biological replicates consisting of 20 plantlets per treatment were selected. After 6 h of incubation in the climate chamber, 10 plantlets per batch were removed from the treatment (Myc-LCOs or Nod-LCOs) or control solutions and harvested, while the other 10 remained in the respective solutions for a total of 24 h. During harvest, one mm of the root tip of each plantlet was removed and discarded. The remaining 2 to 2.5 cm of the distal root region were cut off and directly frozen in liquid nitrogen.