Proteomic changes associated with freeze‐thaw injury and post‐thaw recovery in onion (Allium cepa L.) scales

ABSTRACT The ability of plants to recover from freeze‐thaw injury is a critical component of freeze‐thaw stress tolerance. To investigate the molecular basis of freeze‐thaw recovery, here we compared the proteomes of onion scales from unfrozen control (UFC), freeze‐thaw injured (INJ), and post‐thaw recovered (REC) treatments. Injury‐related proteins (IRPs) and recovery‐related proteins (RRPs) were differentiated according to their accumulation patterns. Many IRPs decreased right after thaw without any significant re‐accumulation during post‐thaw recovery, while others were exclusively induced in INJ tissues. Most IRPs are antioxidants, stress proteins, molecular chaperones, those induced by physical injury or proteins involved in energy metabolism. Taken together, these observations suggest that while freeze‐thaw compromises the constitutive stress protection and energy supply in onion scales, it might also recruit ‘first‐responders’ (IRPs that were induced) to mitigate such injury. RRPs, on the other hand, are involved in the injury‐repair program during post‐thaw environment conducive for recovery. Some RRPs were restored in REC tissues after their first reduction right after thaw, while others exhibit higher abundance than their ‘constitutive’ levels. RRPs might facilitate new cellular homeostasis, potentially by re‐establishing ion homeostasis and proteostasis, cell‐wall remodelling, reactive oxygen species (ROS) scavenging, defence against possible post‐thaw infection, and regulating the energy budget to sustain these processes. Post‐thaw recovery from a mild yet significantly injurious frost event is an important component of ultimate frost‐survival of plant tissues, however, very little is known about the cellular / molecular mechanism of such recovery. Here, we provide the first report of the proteomic changes related to post‐thaw recovery using onion scale as a model system. A total of 58 recovery‐specific proteins were identified, including those involved in ion‐homeostasis, proteostasis, ROS‐scavenging, pathogenesis resistance, cell‐wall remodeling, methionine metabolism and carbohydrate / energy metabolism. Potential roles for these proteins are discussed and a model is proposed to illustrate the key cellular events contributing to tissue recovery.