Proc. Natl Acad. Sci. USA http://doi.org/4qc (2015)

Existing as they do beneath the surface of the soil, the diverse forms and behaviours of roots are often overlooked. Caroline Gutjahr et al. have employed proteomic techniques to illuminate the molecular variations underlying the morphological variety of rice roots and the different ways particular root types respond to arbuscular mycorrhizae.

The authors collected three main root types from rice: crown roots — which connect directly to the stem of the rice plant — as well as large- and fine lateral roots. The roots showed distinct patterns of transcription with over 5,000 genes expressed at significantly different levels between crown roots and fine laterals. Crown roots produced more transcripts involved in responses to hormones and secondary cell wall metabolism. Lateral roots had higher levels of inorganic-ion transporters showing their greater involvement in nutrient uptake. All root types showed large changes in response to inoculation with the mycorrhizal fungus Rhizophagus irregularis. Although less heavily colonized than lateral roots, the crown roots changed the most. The profile of a colonized crown root was more similar to that of a large lateral root than to its former, uncolonized state.

Gutjahr et al. provide a detailed picture of the differing character of root types illustrating both the diversity of a plant's belowground organs and their plasticity in response to the subterranean environment.