Cold shock treatment delays broccoli flower bud yellowing by repressing the gene expression of glycine-rich RNA-binding protein 2, a senescence-associated protein involved in the regulation of stomata opening

Abstract

Broccoli is a globally appreciated vegetable with high nutritional and market value. The quality of harvested broccoli deteriorates quickly due to senescence induced by postharvest stresses. Glycine-rich RNA-binding proteins (GR-RBPs) are RNA chaperones that mediate physiological processes such as stress responses in plants. However, knowledge about their presence and functions in broccoli is lacking. Here, through proteomic analysis we identified GR-RBP2 along with the other 49 senescence-associated proteins (SAPs) in broccoli florets. We further identified 8 GR-RBP genes, including BoGR-RBP2.1, BoGR-RBP2.2, BoCSP1.1, BoCSP1.2, BoCSP2, BoCSP3, BoCSP4.1, and BoCSP4.2, in broccoli transcriptome. The expression of these genes during 20 and 5 °C storage and in response to cold shock treatment (CST) was investigated. BoGR-RBP2.1, BoGR-RBP2.2, BoCSP1.2, BoCSP2, and BoCSP4.1 were upregulated during 20 °C storage, whereas the induction was diminished at 5 °C. CST suppressed the induction of BoGR-RBP2.1 and BoGR-RBP2.2 during 20 and 5 °C storage, respectively, while alleviating water loss and yellowing of broccoli florets stored under both conditions. In addition, scanning electron microscopy demonstrated that the enhanced stomata opening in broccoli florets coincided with BoGR-RBP2s induction, whereas CST restricted the opening in parallel with the repression of BoGR-RBP2s. BoCSP4.2 appeared to be a cold responsive gene induced by 5 °C storage, while it was less related to broccoli florets senescence. In conclusion, we show here that GR-RBP2 is an SAP involved in the modulation of stomata opening in broccoli florets and elucidate the regulation of GR-RBP genes during ambient temperature storage, refrigeration, and upon CST. These findings shed light on the study of RNA chaperones in postharvest stress.