Abstract :
[en] Back to the roots: molecular characterization of cassava root responses during drought and post-harvest stresses
E.M. Lentz1, E. Nyaboga1,2, C. Orek1,3, W. Gruissem1, H. Vanderschuren1,4
1 ETH Zurich, Institute of Agricultural Sciences, Plant Biotechnology Lab, Switzerland
2 International Institute of Tropical Agriculture, Nairobi, Kenya
3 South Eastern Kenya University, Department of DryLand Agriculture, Kitui, Kenya
4 University of Liège, Gembloux Agro-Bio Tech, Plant Genetics Lab, Belgium
The root crop cassava has gained increasing importance in Africa and Asia over the last decade. Cassava starchy roots are not only used as a staple in many tropical countries; they also supply high quality starch to the industry. In the present work we focused on two traits associated with cassava roots, namely post-harvest physiological deterioration (PPD) of cassava storage roots and root system architecture (RSA) under drought stress.
PPD is a major constraint to trade and industrial use of cassava. The quality of the storage roots rapidly diminishes after harvest due to the development of vascular streaking within 24 – 72 hours. In order to identify key pathways and players in the onset of PPD, we used label-free quantification to generate the largest proteome map of cassava root and identify pathways and candidate genes to delay PPD. Our results indicate that the insufficient ROS scavenging capacity of cassava roots can be corrected by root-enhanced transgenic expression of an arabidopsis glutathione peroxidase to generate cassava with delayed onset of PPD.
Despite a drought-adapted physiology, cassava production remains constrained by drought in several regions of the world, including North East Brazil and East Africa. Using mini-rhizotrons we characterized the RSA of selected cassava varieties under drought stress. We identified a cassava variety with a reproducible RSA under moderate water stress: longer fibrous roots with enhanced gravitropic phenotype as well as fewer and shorter lateral roots as compared to well watered control plants. RNA-Seq analysis of root tips suggests that different mechanisms are involved in the alteration of the RSA. The deep rooting phenotype would be triggered by the adjustment of cell expansion, root to shoot ratio and meristem activity and controlled by altered expression of genes coding for MYB transcription factors, proline-rich extensin-like receptor kinases, miRNA, and enzymes involved in gibberellin metabolism. RNASeq data suggest that gravitropism and RSA could be modified by the alteration of expression of a few selected candidate genes.
