Salt stress is one of the most representative abiotic stresses that severely affect plant growth and development. MicroRNAs (miRNAs) are well known for their significant involvement in plant responses to abiotic stresses. Although miRNAs implicated in salt stress response have been widely reported in numerous plant species, their regulatory roles in the adaptive response to salt stress in radish (Raphanus sativus L.), an important root vegetable crop worldwide, remain largely unknown. Solexa sequencing of two sRNA libraries from NaCl-free (CK) and NaCl-treated (Na200) radish roots were performed for systematical identification of salt-responsive miRNAs and their expression profiling in radish. Totally, 136 known miRNAs (representing 43 miRNA families) and 68 potential novel miRNAs (belonging to 51 miRNA families) were identified. Of these miRNAs, 49 known and 22 novel miRNAs were differentially expressed under salt stress. Target prediction and annotation indicated that these miRNAs exerted a role by regulating specific stress-responsive genes, such as squamosa promoter binding-like proteins (SPLs), auxin response factors (ARFs), nuclear transcription factor Y (NF-Y) and superoxide dismutase [Cu-Zn] (CSD1). Further functional analysis suggested that these target genes were mainly implicated in signal perception and transduction, regulation of ion homeostasis, basic metabolic processes, secondary stress responses, as well as modulation of attenuated plant growth and development under salt stress. Additionally, the expression patterns of ten miRNAs and five corresponding target genes were validated by reverse-transcription quantitative PCR (RT-qPCR). With the sRNA sequencing, salt-responsive miRNAs and their target genes in radish were comprehensively identified. The results provide novel insight into complex miRNA-mediated regulatory network of salt stress response in radish, and facilitate further dissection of molecular mechanism underlying plant adaptive response to salt stress in root vegetable crops.

Iron (Fe) is an essential element for plant growth and development, whereas cadmium (Cd) is non-essential and highly toxic. Previous studies showed that Fe deficiency enhanced Cd uptake and accumulation in peanuts. However, the molecular mechanism underlying the increased Cd accumulation in Fe-deficient peanut plants is poorly understood. We employed a comparative transcriptome analysis approach to identify differentially expressed genes (DEGs) in peanut roots exposed to Fe-sufficient without Cd, Fe-deficient without Cd, Fe-sufficient with Cd and Fe-deficient with Cd. Compared with the control, Fe deficiency induced 465 up-regulated and 211 down-regulated DEGs, whereas the up- and down-regulated DEGs in Cd exposed plants were 329 and 189, respectively. Under Fe-deficient conditions, Cd exposure resulted in 907 up-regulated DEGs and 953 down-regulated DEGs. In the presence of Cd, Fe deficiency induced 1042 up-regulated and 847 down-regulated genes, respectively. Based on our array data, we found that metal transporter genes such as CAX4, COPT1, IRT1, NRAMP5, OPT3, YSL3, VIT3 and VIT4 might be involved in iron homeostasis. Moreover, combined with quantitative real-time PCR, IRT1, NRAMP3, NRAMP5, OPT3, YSL3, ABCC3, ZIP1, and ZIP5 were verified to be responsible for Cd uptake and translocation in peanut plants under iron deficiency. Additionally, a larger amount of ABC transporter genes was induced or suppressed by iron deficiency under Cd exposure, indicating that this family may play important roles in Fe/Cd uptake and transport. The up-regulated expression of NRAMP5 and IRT1 genes induced by iron deficiency may enhance Cd uptake in peanut roots. The decrease of Cd translocation from roots to shoots may be resulted from the down-regulation of ZIP1, ZIP5 and YSL3 under iron deficiency.

Peanut is one of the most important oil and protein crops, and it exhibits wide cultivar variations in shoot Cd accumulation ability. However, the mechanism of Cd accumulation in peanut shoots has not been well understood. In this study, the root proteomics of two cultivars differing in seed Cd accumulation, Fenghua 1 (F, low Cd cultivar) and Silihong (S, high Cd cultivar), were investigated under 0 (CK) and 2 μM Cd conditions. A total of 4676 proteins were identified by proteomics screening. Of them, 375, 1762, 1276 and 771 proteins were identified to be differentially expressed proteins (DEPs) for comparison of FCd/FCK, SCd/SCK, FCK/SCK and FCd/SCd, respectively. Silihong is more sensitive to Cd exposure than Fenghua 1 in terms of root proteomics. A total of 30 and 86 DEPs were identified to be related with heavy metal transport and cell wall modification, respectively. The up-regulation of ABCB25, ABCC14, ABCC2, PDR1 and V-ATPases by Cd exposure in Silihong might enhance vacuolar sequestration of Cd and its efflux from symplast to apoplast. The higher Cd accumulation in the root CWs of Silihong might be resulted from its higher capability of CW modification, in which many proteins such as IRX10L, BGLU12-like, BGLU42, EXLB1, XTH30, XTH6, XYL7, PAL3, COMT, CAD1, and CCR1 were involved. The vacuolar sequestration and efflux of Cd as well as its adsorption in CW might be the principal mechanism of cadmium detoxification in Silihong. The higher capacity of Cd accumulation and translocation of Silihong is an inherent characteristics in which ACA8 and ZIP1 might be involved.

Peanut is the world’s fourth largest oilseed crop that exhibits wide cultivar variations in cadmium (Cd) accumulation. To establish the mechanisms of Cd distribution and accumulation in peanut plants, eight cDNA libraries from the roots of two contrasting cultivars, Fenghua 1 (low-Cd cultivar) and Silihong (high-Cd cultivar), were constructed and sequenced by RNA-sequencing. The expression patterns of 16 candidate DEGs were validated by RT-qPCR analysis. A total of 75,634 genes including 71,349 known genes and 4484 novel genes were identified in eight cDNA libraries, among which 6798 genes were found to be Cd-responsive DEGs and/or DEGs between these two cultivars. Interestingly, 183 DEGs encoding ion transport related proteins and 260 DEGs encoding cell wall related proteins were identified. Among these DEGs, nine metal transporter genes (PDR1, ABCC4 and ABCC15, IRT1, ZIP1, ZIP11, YSL7, DTX43 and MTP4) and nine cell wall related genes (PEs, PGIPs, GTs, XYT12 CYP450s, LACs, 4CL2, C4H and CASP5) showed higher expression in Fenghua 1 than in Silihong. Both the metal transporters and cell wall modification might be responsible for the difference in Cd accumulation and translocation between Fenghua 1 and Silihong. These findings would be useful for further functional analysis, and reveal the molecular mechanism responsible for genotype difference in Cd accumulation.