Transcriptomic Analysis of Heat Stress Response in Brassica rapa L. ssp. pekinensis with Improved Thermotolerance through Exogenous Glycine Betaine

Abstract

Chinese cabbage (Brassica rapa L. ssp. pekinensis) is sensitive to high temperature, which will cause the B. rapa to remain in a semi-dormancy state. Foliar spray of GB prior to heat stress was proven to enhance B. rapa thermotolerance. In order to understand the molecular mechanisms of GB-primed resistance or adaptation towards heat stress, we investigated the transcriptomes of GB-primed and non-primed heat-sensitive B. rapa ‘Beijing No. 3’ variety by RNA-Seq analysis. A total of 582 differentially expressed genes (DEGs) were identified from GB-primed plants exposed to heat stress relative to non-primed plants under heat stress and were assigned to 350 gene ontology (GO) pathways and 69 KEGG (Kyoto Encyclopedia of Genes and Genomes) pathways. The analysis of the KEGG enrichment pathways revealed that the most abundantly up-regulated pathways were protein processing in endoplasmic reticulum (14 genes), followed by plant hormone signal transduction (12 genes), ribosome (8 genes), MAPK signaling pathway (8 genes), homologous recombination (7 genes), nucleotide excision repair metabolism (5 genes), glutathione metabolism (4 genes), and ascorbate and aldarate metabolism (4 genes). The most abundantly down-regulated pathways were plant-pathogen interaction (14 genes), followed by phenylpropanoid biosynthesis (7 genes); arginine and proline metabolism (6 genes); cutin, suberine, and wax biosynthesis (4 genes); and tryptophan metabolism (4 genes). Several calcium sensing/transducing proteins, as well as transcription factors associated with abscisic acid (ABA), salicylic acid (SA), auxin, and cytokinin hormones were either up- or down-regulated in GB-primed B. rapa plants under heat stress. In particular, expression of the genes for antioxidant defense, heat shock response, and DNA damage repair systems were highly increased by GB priming. On the other hand, many of the genes involved in the calcium sensors and cell surface receptors involved in plant innate immunity and the biosynthesis of secondary metabolites were down-regulated in the absence of pathogen elicitors in GB-primed B. rapa seedlings. Overall GB priming activated ABA and SA signaling pathways but deactivated auxin and cytokinin signaling pathways while suppressing the innate immunity in B. rapa seedlings exposed to heat stress. The present study provides a preliminary understanding of the thermotolerance mechanisms in GB-primed plants and is of great importance in developing thermotolerant B. rapa cultivars by using the identified DEGs through genetic modification.

Hub Gene Identification and Heat-Stress-Related Transcriptional Regulation Mechanism in Cabbage (Brassica oleracea L.)

“…In the process of responding to heat stress, 1720 and 6178 DEGs were identified in Clematis lanuginosa and Clematis crassifolia, respectively [45]. In the Brassica genus, the number of DEGs in response to heat stress is correlated with various factors, including cultivar, temperature, treatment duration, and tissue type [46][47][48][49]. In our study, 11,579 and 14,707 DEGs were identified in response to heat stress treatment for 4 and 12 h, respectively.…”

Integrated Analysis of the Transcriptome and Metabolome of Brassica rapa Revealed Regulatory Mechanism under Heat Stress

“…Compared with the metabolomic data, JA and SA were significantly downregulated in the plant hormone transduction pathway, while IAA and ERF signaling were upregulated in the plant hormone transduction pathway, which was consistent with the transcriptome results. Recently, Quan et al reported that the thermotolerance of Brassica rapa in heat stress responses could be improved through exogenous glycine betaine (GB) [ 30 ]. In this study, ABA, SA, auxin, and cytokinin (CK) hormones were either up– or downregulated in GB–primed Brassica rapa plants under heat stress.…”