Comparative Transcriptome Profiling Reveals Key MicroRNAs and Regulatory Mechanisms for Aluminum Tolerance in Olive.

Aluminum toxicity (Al) is one of the major constraints to crop production in acidic soils. MicroRNAs (miRNAs) have emerged as key regulatory molecules at post-transcriptional levels, playing crucial roles in modulating various stress responses in plants. However, miRNAs and their target genes conferring Al tolerance are poorly studied in olive (Olea europaea L.). Here, genome-wide expression changes in miRNAs of the roots from two contrasting olive genotypes Zhonglan (ZL, Al-tolerant) and Frantoio selezione (FS, Al-sensitive) were investigated by high-throughput sequencing approaches. A total of 352 miRNAs were discovered in our dataset, consisting of 196 conserved miRNAs and 156 novel miRNAs. Comparative analyses showed 11 miRNAs have significantly different expression patterns in response to Al stress between ZL and FS. In silico prediction identified 10 putative target gene of these miRNAs, including MYB transcription factors, homeobox-leucine zipper (HD-Zip) proteins, auxin response factors (ARF), ATP-binding cassette (ABC) transporters and potassium efflux antiporter. Further functional classification and enrichment analysis revealed these Al-tolerance associated miRNA-mRNA pairs are mainly involved in transcriptional regulation, hormone signaling, transportation and metabolism. These findings provide new information and perspectives into the regulatory roles of miRNAs and their target for enhancing Al tolerance in olives.

Effect of combined application of lead, cadmium, chromium and copper on grain, leaf and stem heavy metal contents at different growth stages in rice.

Most studies on plants' response to heavy metal toxicity have been focusing on single metals. However, soils are always contaminated by several kinds of heavy metals. In this study, pot experiments were carried out to investigate the effects of combined toxicity on two rice genotypes differing in Cd accumulation (Xiushui817, a low-grain-Cd-accumulation and Zheda821, a high-grain-Cd-accumulation genotype). Yield, heavy metal concentrations of grain and leaf/stem at different growth stages were measured under combined application of Cd, Cr, Pb and Cu. Yield was significantly decreased under higher Pb and Cd treatment in both genotypes with Xiushui817 showing greater reduction. Increasing soil Cu level showed no significant effect on grain yield. Zheda821 consistently showed a higher grain Cd content than Xiushui817. The application of Pb, Cd, Cr and Cu significantly affected grain Cd, Cr and Cu accumulations. Similar trends were also observed in leaves and stems at harvest stage. The critical levels of leaf/stem Cd and Cr for safe rice production were also estimated. Alleviation measures should be taken to decrease Cd or Cr accumulations in grain of rice if leaf or stem Cd or Cr concentrations at different growth stages exceed the critical levels.

DNA microarray revealed and RNAi plants confirmed key genes conferring low Cd accumulation in barley grains.

BACKGROUND: Understanding the mechanism of low Cd accumulation in crops is crucial for sustainable safe food production in Cd-contaminated soils. RESULTS: Confocal microscopy, atomic absorption spectrometry, gas exchange and chlorophyll fluorescence analyses revealed a distinct difference in Cd accumulation and tolerance between the two contrasting barley genotypes: W6nk2 (a low-grain-Cd-accumulating and Cd-sensitive genotype) and Zhenong8 (a high-grain-Cd-accumulating and tolerant genotype). A DNA microarray analysis detected large-scale changes of gene expression in response to Cd stress with a substantial difference between the two genotypes. Cd stress led to higher expression of genes involved in transport, carbohydrate metabolism and signal transduction in the low-grain-Cd-accumulating genotype. Novel transporter genes such as zinc transporter genes were identified as being associated with low Cd accumulation. Quantitative RT-PCR confirmed our microarray data. Furthermore, suppression of the zinc transporter genes HvZIP3 and HvZIP8 by RNAi silencing showed increased Cd accumulation and reduced Zn and Mn concentrations in barley grains. Thus, HvZIP3 and HvZIP8 could be candidate genes related to low-grain-Cd-accumulation. CONCLUSION: Novel transporter genes such as HvZIP3 and HvZIP8 were identified as being associated with low-grain-Cd-accumulation. In addition to advancing academic knowledge, our findings may also result in potential economic benefits for molecular breeding of low Cd accumulating barley and other crops.

Comparative proteomic analysis of two tobacco (Nicotiana tabacum) genotypes differing in Cd tolerance.

Tobacco can easily accumulate cadmium (Cd) in leaves and thus poses a potential threat to human health. Cd-stress-hydroponic-experiments were performed, and the proteomic and transcriptional features of two contrasting tobacco genotypes Yun-yan2 (Cd-tolerant) and Guiyan1 (Cd-sensitive) were compared. We identified 18 Cd-tolerance-associated proteins in leaves, using 2-dimensional gel electrophoresis coupled with mass spectrometry, whose expression were significantly induced in Yunyan2 leaves but down-regulated/unchanged in Guiyan1, or unchanged in Yunyan2 but down-regulated in Guiyan1 under 50 µM Cd stress. They are including epoxide hydrolase, enoyl-acyl-carrier-protein reductase, NPALDP1, chlorophyll a-b binding protein 25, heat shock protein 70 and 14-3-3 proteins. They categorized as 8 groups of their functions: metabolism, photosynthesis, stress response, signal transduction, protein synthesis, protein processing, transport and cell structure. Furthermore, the expression patterns of three Cd-responsive proteins were validated by quantitative real-time PCR. Our findings provide an insight into proteomic basis for Cd-detoxification in tobacco which offers molecular resource for Cd-tolerance.