PpBZR1, a BES/BZR transcription factor, enhances cold stress tolerance by suppressing sucrose degradation in peach fruit

Abstract

Brassinolides (BRs) are phytohormones that play numerous roles in a plants’ response to environmental stress. While BES/BZR transcription factors are essential components in BR signaling, their role in regulating postharvest fruit responses to cold stress is largely unknown. In this study, the application of 24-epibrassinolide (EBR) to peaches alleviated chilling injury (CI) during postharvest cold storage. We further characterized a key BES/BZR gene,PpBZR1, which regulates peach cold resistance. Transient expression PpBZR1in peaches showed that PpBZR1 inhibits PpVIN2 expression and VIN activity, resulting in an elevated level of sucrose, which protects fruit from CI. Arabidopsis expressing PpBZR1 had a high germination and seedling survival rate at low temperatures, which may be due to higher level of sucrose and lower oxidative damage. Mechanistically, we confirmed that PpBZR1 directly binds to the PpVIN2 promoter and functions as a negative regulator. In addition, PpCBF1/5/6 were induced by EBR treatment and AtCBFswere upregulated in transgenic Arabidopsis. Combined with previous findings, we hypothesize that PpBZR1 regulates PpVIN2 through a CBF-dependent manner. In conclusion, PpBZR1 expression is induced by EBR treatment during cold storage, and PpBZR1 futher inhibite sucrose degradation gene PpVIN2transcription via direct binding its promoter and indirectly regulating PpVIN2. This CBF-dependent and CBF-independent regulation results in slower sucrose degradation and higher chilling tolerance of peach.

Biochemical and molecular changes in peach fruit exposed to cold stress conditions

“…The link between sugar metabolism and CI has been also reported in fruits such as pear, banana, tomato, bell pepper, and pomegranate (Delgado‐Vargas et al 2022 ; Gómez et al 2009 ; Liu et al 2019a ; Lorente-Mento et al 2023 ; Xu et al 2023 ; Yang et al 2023 ). Several studies reported how the increased tolerance to CI observed in fruits in response to the application of exogenous treatments was connected to the enhancement of sugar metabolism (Zhang et al 2021 ). For example, heat treated peaches showed an increase in fucose, raffinose, maltitol, glucose, isomaltose, sucrose, and sorbitol, and at the same time they showed less CI symptoms (Lurie 2022 ).…”

“…Low temperatures can lead to changes in the expression of cell wall-related proteins, including expansins, pectin methylesterases, and xyloglucan endotransglucosylase/ hydrolase (XTH) enzymes. These proteins are involved in cell wall remodelling and may contribute to the softening and cell breakdown observed in chilled peaches (Zhang et al 2023). A CI study performed on peach demonstrated that endopolygalacturonase, CAT, NADPdependent isocitrate dehydrogenase, pectin methylesterase, and dehydrins were differentially accumulated between control and chill injured fruit (Nilo et al 2010).…”

“…Similarly, Zhao et al (2021a) showed that the exogenous application of Jasmonic Acid alleviates chilling injury and reduces the internal browning of peach fruit by promoting sugar and ethylene metabolism. Other exogenous treatments such as 1-methylcyclopropene (1-MCP), methyl salicylate, 24-epibrassinolide (EBR), glycine betaine (GB), and oxalic acids resulted in increasing sucrose content and chilling tolerance in peach fruit by activating energy metabolism (Wang et al 2019;Yu et al 2017;Zhang et al 2023). Thus, although an association between increased sugar content and CI appears in several studies it is not universal, and the specific sugars reported vary.…”