The dynamics of DNA methylation in maize roots under Pb stress.

Plants adapt to adverse conditions through a series of physiological, cellular, and molecular processes, culminating in stress tolerance. However, little is known about the associated regulatory mechanisms at the epigenetic level in maize under lead (Pb) stress. Therefore, in this study, we aimed to compare DNA methylation profiles during the dynamic development of maize roots following Pb treatment to identify candidate genes involved in the response to Pb stress. Methylated DNA immunoprecipitation-sequencing (MeDIP-seq) was used to investigate the genome-wide DNA methylation patterns in maize roots under normal condition (A1) and 3 mM Pb(NO3)2 stress for 12 h (K2), 24 h (K3) and 48 h (K4). The results showed that the average methylation density was the highest in CpG islands (CGIs), followed by the intergenic regions. Within the gene body, the methylation density of the introns was higher than those of the UTRs and exons. In total, 3857 methylated genes were found in 4 tested samples, including 1805 differentially methylated genes for K2 versus A1, 1508 for K3 versus A1, and 1660 for K4 versus A1. Further analysis showed that 140 genes exhibited altered DNA methylation in all three comparisons, including some well-known stress-responsive transcription factors and proteins, such as MYB, AP2/ERF, bZIP, serine-threonine/tyrosine-proteins, pentatricopeptide repeat proteins, RING zinc finger proteins, F-box proteins, leucine-rich repeat proteins and tetratricopeptide repeat proteins. This study revealed the genome-scale DNA methylation patterns of maize roots in response to Pb exposure and identified candidate genes that potentially regulate root dynamic development under Pb stress at the methylation level.

Transcriptional responses of maize seedling root to phosphorus starvation.

Maize (Zea mays) is the most widely cultivated crop around the world, however, it is commonly affected by phosphate (Pi) deficiency and the underlying molecular basis of responses mechanism is still unknown. In this study, the transcriptional response of maize roots to Pi starvation at 3 days after the onset of Pi deprivation was assessed. The investigation revealed a total of 283 Pi-responsive genes, of which 199 and 84 genes were found to be either up- or down-regulated respectively, by 2-fold or more. Pi-responsive genes were found to be involved in sugar and nitrogen metabolic pathways, ion transport, signal transduction, transcriptional regulation, and other processes related to growth and development. In addition, the expression patterns of maize inorganic phosphorus transporters, acid phosphatase, phytase, 2-deoxymugineic acid synthase1, POD and MYB transcription factor were validated in 178 roots response to low phosphorus stress. of which, two genes encoding phytase and acid phosphatase were significantly induced by Pi deficiency and may play a pivotal role in the process of absorption and re-utilization of Pi in Maize. These results not only enhance our knowledge about molecular processes associated with Pi deficiency, but also facilitate the identification of key molecular determinants for improving Pi use in maize. Moreover, this work sets a framework to produce Pi-specific maize microarrays to study the changes in global gene expression between Pi-efficient and Pi-inefficient maize genotypes.

[Heavy metal-transport proteins in plants: a review].

The heavy metals in soil not only damage plant growth, but also threaten the health of human beings and animals through food chain. Heavy metal-transport proteins play crucial roles in the heavy metals uptake and tolerance of plants. Plant heavy metal-transport proteins can be classified as metal-uptake proteins and metal-efflux proteins. The metal-uptake proteins can transport essential heavy metals into cytoplasm, and also, transport toxic heavy metals into cytoplasm due to the absence of essential heavy metals or the competition among ions. The metal-efflux proteins are a group of detoxification proteins, which can efflux excess and toxic heavy metals from cytoplasm, or move these metals into vacuole. In recent years, the associations between elevated steady-state transcript levels of heavy metal-transporter genes and metal accumulation in plants have been revealed, and many heavy metal-transport proteins have been cloned and identified. In this paper, the metal affinity, tissue-specific gene expression, and cellular location of representative heavy metal-transport proteins were reviewed.

[Identification of known microRNAs in root and leaf of maize by deep sequencing].

microRNA (miRNAs) is a newly identified class of 20-24 nt non-protein-coding and endogenous small RNA, which plays an important role in plant growth, development and response to environmental stresses. Combined with bioinformatic method, the types, abundance, and targets of known miRNAs in root and leaf of maize (Zea mays L.) were analyzed by small RNA deep sequencing technology, which was based on Illumina/Solexa principium. The results indicated that 92 known miRNAs were detected in maize root, which were attributed to 18 miRNA families and their abundance ranged from 1 to 105,943 reads. Synchronously, 86 known miRNAs were detected in maize leaf, which were attributed to 17 miRNA families and their abundance ranged from 1 to 85,973 reads. The target gene prediction showed that 54 putative target genes as these known miRNAs were predicted. Some of them were involved in the following processes, such as transcription regulation, substance and energy metabolism, electron transport, stress response, and signal transduction through further function prediction. In conclusion, there were obvious differences in both types and abundance of known miRNAs between root and leaf in maize.

[Advances in study of plant miRNAs under stressed environmental conditions].

Biotic and abiotic stresses influence plant growth and cause great loss to crop yield. In the long course of evolution, plants have developed intricate biological mechanism to resist stressed conditions. Under various stressed conditions, not only the protein-coding genes, but also the non-protein-coding genes were induced for response. More and more researches showed that the transcripts of these non-protein-coding genes played important role in regulation of gene expression. miRNA is one of the groups in these no-coding regulatory small RNAs. Recent findings showed that in order to resist the biotic and abiotic stresses, expression of microRNA (miRNA) genes will be induced and their transcripts (miRNAs) can regulate gene expression by guiding target mRNA cleavage or translation inhibition. This paper focused on the advances of plant miRNAs research in stressed conditions, especially induced expression of miRNA and target gene regulation and its role on adaptation under stressed conditions. Then, the methods of miRNA researches in stressed environments are discussed.

[Advances of microarray analysis on plant gene expression under environmental stresses].

Different stressed conditions impair plant growth and further, cause great loss of crop yield and even lead to lose production completely. Increasing resistance/tolerance of crops under stressed conditions is a major goal of numerous plant breeders, and many elegant works are focusing on this area to uncover these complicated mechanisms underlying it. However, the traditional strategies including physiological and biochemical methods, as well as studies on a few genes, can not well understand the overall biological mechanism. Microarray analysis opens a door to uncover these cryptic mechanisms, and has the ability of detecting gene transcription and regulation at genomic level in different plant tissues. And works in association with related methods of proteomics and metabolomics. Therefore, it is possible to locate genes in certain key metabolism pathways. Through these procedures, it is also possible to look for critical genes in the pathway and to well understand the molecular mechanism of resistance/tolerance. These results can be as a guidance for increasing the resistance/tolerance of stressed conditions using biotechnology methods in future. This paper mainly focused on and discussed the advances of microarray analysis of stressed conditions-related genes in plants.