Genome Wide Association Study, transcriptome and biochemical analyses provide insights into the root hydrotropic response of maize (Zea mays L.).
The subsistence of terrestrial plants depends upon the ability of roots to absorb water and nutrients from the soil. Directed growth of the primary root from a layer of the soil with low water content towards a zone with high water content is known as hydrotropism. This tropic response enables the root to reach soil with the proper humidity for plant growth, and therefore avoid drought conditions. Although the shortage of sufficient water is the single-most critical factor affecting world agriculture, there are very few studies on hydrotropism in crop plants. The strength of the hydrotropic response (angle of curvature) of the maize primary root in maize varies enormously. After phenotyping root hydrotropism in 231 Drought Tolerant Maize for Africa hybrids, we performed a Genome Wide Association Study and found two candidate genes that regulate the ubiquitin/26 proteasome system. We also compared the root transcriptomes between maize accessions with contrasting hydrotropic response after 6 h of hydro stimulation: (CML376<2/NVOL46)-74-1-1-B) (robust response) and (CML376<2/SNL17)-28-1-1-B) (weak response). This analysis revealed that hydrotropism in maize seems to be regulated by chaperones, heat shock proteins, late embryogenesis abundant proteins, and ubiquitin ligases. Furthermore, we biochemically examined the role of protein ubiquitination and protein degradation during hydrotropism. Our results suggest that the signal transduction pathways induced by hydro stimulation in maize are like those triggered by heat, water stress, and protein ubiquitination.