Proline as a probable biomarker of cold stress tolerance in Sorghum (Sorghum bicolor)

Plants have developed physiological and molecular mechanisms to support and adapt to adverse environments. One response to abiotic stress is the accumulation of free proline (PRO). PRO can induce the expression of many genes, which have the proline-responsive element (PRE) in their promoters, nevertheless due to the complexity of interactions between stress factors and various molecular, biochemical and physiological phenomena it is still unclear whether a more efficient PRO accumulation can be considered a biomarker of tolerance in plants. In the present work, we evaluated the accumulation of PRO in two genotypes of sorghum with contrasting tolerance to cold stress. To explore the cause behind the accumulation of proline under cold stress conditions, we identified the Transcription Factors Binding Sites (TFBS) present in the promoter regions in the genes involved in the biosynthesis and degradation of proline in sorghum and other important crops, finding that the untranslated 3 'region P5CS gene contains different TFBS. We found TFBS that could allow the activation of genes involved in proline biosynthesis through the ornithine pathway under cold stress conditions, suggesting that ornithine route can be activated under cold stress conditions