Quantitative Proteomic Analyses Reveal That Energy Metabolism and Protein Biosynthesis Reinitiation are Responsible for the Initiation of Bolting Induced by High Temperature in Lettuce (Lactuca sativa L.)

Abstract

Background Lettuce (Lactuca sativa L.), one of the most economically important leaf vegetables, exhibits early bolting under high-temperature conditions. Early bolting leads to loss of commodity value and edibility, leading to considerable loss and waste of resources. However, the initiation and molecular mechanism underlying early bolting induced by high temperature remains largely elusive. Results To better understand this phenomenon, the bolting initiation period of lettuce was defined, and a comparative proteomic analysis was conducted in the initiation period of bolting induced by a high temperature (33 °C) and a control temperature (20 °C) using iTRAQ-based proteomics, phenotypic measurement, and biological verification by RT-qPCR. Morphological and microscopic observation showed that the initiation of bolting occurred 8 days after high-temperature treatment. Fructose rapidly accumulated after high-temperature treatment. During bolting initiation, of the 3305 identified proteins, a total of 93 proteins exhibited differential abundances, 38 of which were up-regulated, and 55 were down-regulated. Approximately 38% of the proteins were involved in metabolic pathways and were mainly clustered in energy metabolism and protein synthesis. Furthermore, some proteins involved in sugar synthesis were differentially expressed, which were also associated with energy production. Conclusions This is the first report on the metabolic changes involved in bolting initiation in lettuce. Our study suggested that energy metabolism and ribosomal proteins are pivotal components during bolting initiation. This study could provide a potential regulatory mechanism for the initiation of early bolting by high temperature, which could have applications in the manipulation of lettuce for breeding.