Functional Analysis of Drought-Responsive Proteins in Kentucky Bluegrass Cultivars Differing in Drought Tolerance.

Identification and functional analysis of drought-responsive proteins provides insights into metabolic processes involved in drought tolerance.  The objectives of this study were to identify proteins differentially expressed in two Kentucky bluegrass (Poa pratensis L.) cultivars differing in drought tolerance in response to drought stress and to determine biological functions of differentially-expressed proteins involved in drought tolerance. Plants of ‘Brilliant’ (drought sensitive) and ‘Midnight’ (drought tolerant) were grown under well-watered conditions or subjected to drought stress by withholding water for 15 days in growth chambers. ‘Midnight’ exhibited superior drought tolerance than ‘Brilliant’, as demonstrated by higher relative water content and photochemical efficiency, and lower membrane leakage. Proteins were extracted and separated using differential gel electrophoresis. The sequences of 93 protein spots differentially expressed in two cultivars under well-watered and drought stress were analyzed using mass spectrometry, and 68 spots were identified with known functions.  Many proteins involved in amino acid metabolism or energy metabolism were down-regulated under drought stress in both cultivars, but most were maintained at a higher level in ‘Midnight’ than in ‘Brilliant’.  Two proteins (60 kDa chaperonin and 70 kDa heat shock cognate) accumulated at a higher level in ‘Midnight’ than in ‘Brilliant’ under drought stress. The results demonstrated that drought tolerance in Kentucky bluegrass as associated with maintaining amino acid and energy metabolisms, as well as up-regulation of heat shock proteins serving as chaperones.