Tandem mass tag-based (TMT) quantitative proteomics analysis reveals the response of fine roots to drought stress in cotton (Gossypium hirsutumL.)

Background Cotton (Gossypium hirsutumL.) is one of the most important cash crops worldwide. Fine roots are the central part of the root system that contributes to plant water and nutrient uptake. However, the mechanisms underlying the response of cotton fine roots to soil drought remains unclear. To elucidate the proteomic changes in fine roots of cotton plants under drought stress, 70-75% and 40-45% soil relative water content treatments were imposed on control (CK) and drought stress (DS) groups, respectively. Then, tandem mass tags (TMT) technology was used to determine the proteome profiles of fine root tissue samples. Results Drought significantly decreased the value of average root diameter of cotton seedlings, whereas the total root length and the activities of antioxidases were increased. To study the molecular mechanisms underlying drought response further, the proteome differences between tissues under CK and DS treatments were compared pairwise at 0, 30, and 45 DAD (days after drought stress). In total, 118 differentially expressed proteins (DEPs) were up-regulated and 105 were down-regulated in the 'DS30 versus CK30' comparison; 662 DEPs were up-regulated, and 611 were down-regulated in the 'DS45 versus CK45' comparison. The functions of these DEPs were classified according to their pathways. Under early stage drought (30 DAD), some DEPs involved in the 'Cutin, suberin, and wax synthesis' pathway were up-regulated, while the down-regulated DEPs were mainly enriched within the 'Monoterpenoid biosynthesis' pathway. Forty-five days of soil drought had a greater impact on DEPs involved in metabolism. Many proteins involving 'Carbohydrate metabolism,' 'Energy metabolism,' 'Fatty acid metabolism,' 'Amino acid metabolism,' and 'Secondary metabolite biosynthesis' were identified as DEPs. Additionally, proteins related to ion transport, stress/defense, and phytohormones were also shown to play roles in determining the fine root growth of cotton plants under drought stress. Conclusions Our study identified potential biological pathways and drought-responsive proteins related to stress/defense responses and plant hormone metabolism under drought stress. Collectively, our results provide new insights for further improving drought tolerance in cotton and other crops.