Physiological and proteomic analysis of two contrasting Sorghum bicolor genotypes in response to drought stress

Understanding the response of a crop to drought is the first step in the breeding of tolerant genotypes. In this study, two sorghum (Sorghum bicolor L.) genotypes with contrasting sensitivity to drought were subjected drought stress by withholding water for 7 days at seedling stage; physiological and protein analyses were made. Reduction percentage was recorded on leaf water content, chlorophyll a and b and total chlorophyll. Shoot and root lengths reductions were observed in the drought-sensitive Cultivar (Tabat) while the drought-tolerant line (EL9) showed an increase in shoot and root lengths under drought conditions. Drought tolerant sorghum line EL9 accumulated higher proline (26% increase) when compared to the sensitive cultivar Tabat (5% increase). Mass spectrometry analysis coupled with nanoflow UPLC was used to compare daily-watered with drought stressed (7 days) seedlings. A total of 36 protein spots were detected, of which 23 were recorded for one or both accessions under drought stress conditions only. These proteins were identified using MASCOT database search in accordance with sequence similarity with previously characterized proteins from the Uniprot database. The identified proteins were assigned to different functional categories as follows: Response to stress (35%); metabolic processes (26%); photosynthetic (13%); fatty acid biosynthesis (4%) and cell wall biogenesis/degradation (4%). Seven of the identified proteins under stress condition were unique to El9, in contrast to 4 proteins were unique to Tabat. This study showed a differential protein expression pattern of two sorghum accessions under drought stress, which will be valuable for studying the molecular mechanisms underlying drought tolerance in the future. Also, these proteins could be potential candidates for development of markers to be used in markers assisted selection.