The radish WRKY gene family was genome-widely identified and played critical roles in response to multiple abiotic stresses. The WRKY is among the largest transcription factors (TFs) associated with multiple biological activities for plant survival, including control response mechanisms against abiotic stresses such as heat, salinity, and heavy metals. Radish is an important root vegetable crop and therefore characterization and expression pattern investigation of WRKY transcription factors in radish is imperative. In the present study, 126 putative WRKY genes were retrieved from radish genome database. Protein sequence and annotation scrutiny confirmed that RsWRKY proteins possessed highly conserved domains and zinc finger motif. Based on phylogenetic analysis results, RsWRKYs candidate genes were divided into three groups (Group I, II and III) with the number 31, 74, and 20, respectively. Additionally, gene structure analysis revealed that intron-exon patterns of the WRKY genes are highly conserved in radish. Linkage map analysis indicated that RsWRKY genes were distributed with varying densities over nine linkage groups. Further, RT-qPCR analysis illustrated the significant variation of 36 RsWRKY genes under one or more abiotic stress treatments, implicating that they might be stress-responsive genes. In total, 126 WRKY TFs were identified from the R. sativus genome wherein, 35 of them showed abiotic stress-induced expression patterns. These results provide a genome-wide characterization of RsWRKY TFs and baseline for further functional dissection and molecular evolution investigation, specifically for improving abiotic stress resistances with an ultimate goal of increasing yield and quality of radish.
NAC (NAM, no apical meristem; ATAF, Arabidopsis transcription activation factor and CUC, cup-shaped cotyledon) proteins are among the largest transcription factor (TF) families playing fundamental biological processes, including cell expansion and differentiation, and hormone signaling in response to biotic and abiotic stresses. In this study, 172 RsNACs comprising 17 membrane-bound members were identified from the whole radish genome. In total, 98 RsNAC genes were non-uniformly distributed across the nine radish chromosomes. In silico analysis revealed that expression patterns of several NAC genes were tissue-specific such as a preferential expression in roots and leaves. In addition, 21 representative NAC genes were selected to investigate their responses to heavy metals (HMs), salt, heat, drought and abscisic acid (ABA) stresses using real-time polymerase chain reaction (RT-qPCR). As a result, differential expressions among these genes were identified where RsNAC023 and RsNAC080 genes responded positively to all stresses except ABA, while RsNAC145 responded more actively to salt, heat and drought stresses compared with other genes. The results provides more valuable information and robust candidate genes for future functional analysis for improving abiotic stress tolerances in radish.
Cadmium (Cd) is a widespread heavy metal of particular concern with respect to the environment and human health. Although intensive studies have been conducted on Cd-exposed transcriptome profiling, little systematic proteome information is available on the molecular mechanism of Cd stress response in radish. In this study, the radish root proteome under Cd stress was investigated using a quantitative multiplexed proteomics approach. Seedlings were grown in nutrient solution without Cd (control) or with 10 or 50 μM CdCl2 for 12 h (Cd10 and Cd50, respectively). In total, 91 up- and 66 down-regulated proteins were identified in the control vs Cd10 comparison, while 340 up- and 286 down-regulated proteins were identified in the control vs Cd50 comparison. Functional annotation indicated that these differentially expressed proteins (DEPs) were mainly involved in carbohydrate and energy metabolism, stress and defense and signal transduction processes. Correlation analysis showed that 33 DEPs matched with their transcripts, indicating a relatively low correlation between transcript and protein levels under Cd stress. Quantitative real-time PCR evidenced the expression patterns of 12 genes encoding their corresponding DEPs. In particular, several pivotal proteins associated with carbohydrate metabolism, ROS scavenging, cell transport and signal transduction were involved in the coordinated regulatory network of the Cd stress response in radish. Root exposure to Cd2+ activated several key signaling molecules and metal-containing transcription factors, and subsequently some Cd-responsive functional genes were mediated to reduce Cd toxicity and re-establish redox homeostasis in radish. This is a first report on comprehensive proteomic characterization of Cd-exposed root proteomes in radish. These findings could facilitate unraveling of the molecular mechanism underlying the Cd stress response in radish and provide fundamental insights into the development of genetically engineered low-Cd-content radish cultivars.
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