Transcriptome Analysis Reveals the Different Response to Toxic Stress in Rootstock Grafted and Non-Grafted Cucumber Seedlings

Abstract

Autotoxicity of root exudates is one of the main reasons for consecutive monoculture problem (CMP) in cucumber under greenhouse cultivation. Rootstock grafting may improve the tolerance of cucumber plants to autotoxic stress. To verify the enhanced tolerance to autotoxic stress and illuminate relevant molecular mechanism, a transcriptomic comparative analysis was performed between rootstock grafted (RG) and non-grafted (NG) cucumber plants by a simulation of exogenous cinnamic acid (CA). The present study confirmed that relatively stable plant growth, biomass accumulation, chlorophyll content, and photosynthesis was observed in RG than NG under CA stress. We identified 3647 and 2691 differentially expressed genes (DEGs) in NG and RG cucumber plants when compared to respective control, and gene expression patterns of RNA-seq was confirmed by qRT-PCR. Functional annotations revealed that DEGs response to CA stress were enriched in pathways of plant hormone signal transduction, MAPK signaling pathway, phenylalanine metabolism, and plant-pathogen interaction. Interestingly, the significantly enriched pathway of photosynthesis-related, carbon and nitrogen metabolism only identified in NG, and most of DEGs were down-regulated. However, most of photosynthesis, Calvin cycle, glycolysis, TCA cycle, and nitrogen metabolism-related DEGs exhibited not or slightly down-regulated in RG. In addition, several stress-related transcription factor families of AP2/ERF, bHLH, bZIP, MYB. and NAC were uniquely triggered in the grafted cucumbers. Overall, the results of this study suggest that rootstock grafting improve the tolerance of cucumber plants to autotoxic stress by mediating down-regulation of photosynthesis, carbon, and nitrogen metabolism-related DEGs and activating the function of stress-related transcription factor. The transcriptome dataset provides an extensive sequence resource for further studies of autotoxic mechanism at molecular level.

Grafting-enhanced tolerance of cucumber to toxic stress is associated with regulation of phenolic and other aromatic acids metabolism

“…Cinnamic acid, ferulic acid, p-hydroxybenzoic acid and p-coumaric acid were demonstrated as main autotoxic substances in cucumber, and they have an adverse effect on growth, physiology and soil microbial communities ( Ye et al, 2006 ; Zhou & Wu, 2012 ; Zhou, Yu & Wu, 2012 ; Zhou & Wu, 2018 ). Our previous study also proved the detrimental effect of cinnamic acid on cucumber ( Xiao et al, 2020 ). Biosynthesis of phenolic and other aromatic acids undergoes the general phenylpropanoid pathway (GPP) and subsequent specific branch pathways.…”

“…Previous studies demonstrated that autotoxicity is the main causes of consecutive monoculture problem ( Yu & Matsui, 1994 ; Yu et al, 2003 ). Cinnamic acid, as the main autotoxin, was used to simulate autotoxic stress, and the inhibitory effect on growth was confirmed ( Ye et al, 2006 ; Yu et al, 2003 ; Xiao et al, 2020 ). Although similar result were obtained in the present study, plant biomass of root-grafted cucumber seedlings was barely inhibited; similar findings were reported in eggplant ( Chen et al, 2011 ) and watermelon ( Ling et al, 2013 ).…”

“…Several studies confirmed grafting could help watermelon ( Ling et al, 2013 ) and eggplant ( Chen et al, 2011 ) to resist toxic stress caused by root exudate or autotoxic substances. Likewise, our previous work demonstrated that grafting with figleaf gourd provided a stable plant growth and photosynthetic activity of cucumber under cinnamic acid stress, and revealed the underlying molecular mechanism by transcriptome analysis ( Xiao et al, 2020 ). On the basis of the transcriptomic data, we found that the phenylpropanoid biosynthesis was one of the top five pathways enriched as measured by differentially expressed genes (DEGs) under cinnamic acid treatment.…”

Genome-Wide Analysis of Basic Helix-Loop-Helix (bHLH) TFs in Sea Buckthorn (Hippophae rhamnoides)

“…Based on the highly conserved domains and their evolutionary relationships, this superfamily is mainly divided into 20-25 subfamilies in agronomically important plants. A wide range of extensive studies have been reported on the bHLH superfamily-related genes in plant species after genome sequences have been produced, including cucumber [5], Arabidopsis [7], apple [10], tomato [24] and Carthamus tinctorius [32]. Additionally, functional and structural characterizations of most plant bHLH proteins have been described in detail.…”

“…The bHLH TFs have various functions in plant growth and development. The bHLH genes SPATULA and ALCATRAZ impact the development of carpel and fruit [5,6], and MYC2, MYC3, while the MYC4 affects the owering of Arabidopsis thaliana [7]. The bHLH gene BIGPETALp in A. thaliana plays an important role in controlling petal size [8], and the bHLH gene BIM1 is associated with embryonic patterning [9].…”