Physiological and proteome analysis suggest critical roles for the photosynthetic system for high water-use efficiency under drought stress in Malus

• Higher Pn and photosynthesis mainly contribute to higher WUE.
• Calvin cycle improves Pn in treated cv. ‘Qinguan’.
• Stabilized photosynthetic electron transfer prevents photoinhibition and ROS.

Water use efficiency is an important indicator for plant adaptation and resistance to drought conditions. We previously found that under moderate drought stress, the water use efficiency of cv. ‘Qinguan’ apple (Malus domestica Borkh.) (tolerant to drought) was enhanced, while that of cv. ‘Naganofuji No. 2’ was not enhanced. In this research, we also found that instantaneous water-use efficiency of cv. ‘Qinguan’ was higher than that of cv. ‘Naganofuji No. 2’, mainly because of its higher net photosynthesis rate. To dissect the potential mechanisms underlying this phenomenon, we performed a comparative iTRAQ-based proteomics analysis with leaves of drought-treated cv. ‘Qinguan’ and ‘Naganofuji No. 2’. We identified 4078 proteins, of which 594 were differentially abundant between drought and well-watered leaves. The majority of increased proteins were predicted to be involved in photosynthetic pathway in drought treated cv. ‘Qinguan’ leaves, indicating that regulation of photosynthesis plays an important role for higher water use efficiency under drought stress. Enzyme activity assays were performed to validate the proteomics data. Our results suggested that the main regulatory mechanisms for high water use efficiency of cv. ‘Qinguan’ under moderate drought stress included the maintaining of Calvin cycle function by increasing key enzymes, stabilization of photosynthetic electron transfer and keeping reactive oxygen species at normal level by regulation of photosynthetic electron transfer chain, photorespiration and reactive oxygen species scavenging capability, thus prevented photoinhibition, reduced reactive oxygen species production and enhanced net photosynthesis rate. In addition, the response of signal regulatory proteins and abiotic stress-responsive proteins to drought also helped plants to cope with such stress.

Experimental design and schematic diagram of the workflow used in this study. Two sets of biological replicate samples were analyzed by iTRAQ, using the hpRP-nanoLC–MS/MS workflow for examining proteome changes in apple trees in response to long term moderate drought. Proteins were identified using Mascot software.Figure optionsDownload as PowerPoint slide