PpHsfA2a-regulated the accumulation of proline and polyamines participates in glycine betaine-enhanced chilling resistance in peach fruit

Application of glycine betaine (GB) was found to efficiently alleviate chilling injury (CI) of peach fruit under chilling conditions, but the molecular mechanism of which remains unclear. In this work, GB treatment retained lower internal browning index accompanied by lower relative conductivity and malondialdehyde content in cold stored peaches. Meanwhile, GB treatment elevated the gene transcription and activities of Δ ¹-pyroline-5-carboxylate synthetase (P5CS), ornithine δ-aminotransferase (OAT), arginase (ARG), arginine decarboxylase (ADC) and ornithine decarboxylase (ODC), weakened the gene transcription and activity of proline dehydrogenase (PDH), contributing to the accumulation of proline and polyamines (PAs). Moreover, PpHsfA2a was highly expressed under cold stress and GB treatment, which was further found to be located in the nucleus with transactivation capacity. Importantly, PpHsfA2a activated the expression of PpARG, PpOAT and PpADC by directly recognizing and binding to the HSE elements in their promoters. Consequently, these results suggested that PpHsfA2a-mediated the transcriptional activation of proline and PAs accumulation related genes was involved in GB-enhanced chilling resistance in peach fruit, which was beneficial for the integrity of cell membrane function and structure under cold conditions.