The miRNA-mediated post-transcriptional regulation of maize response to nitrate

Stress responses depend on the correct regulation of gene expression. The discovery that abiotic as well as biotic stresses can regulate miRNA levels, coupled with the identification and functional analyses of stress-associated genes as miRNA targets, provided clues about the vital role that several miRNAs may play in modulating plant resistance to stresses. Nitrogen availability seriously affects crops productivity and environment and the understanding of the miRNA-guided stress regulatory networks should provide new tools for the genetic improvement of nitrogen use efficiency of crops. A recent study revealed the potential role of a number of nitrate-responsive miRNAs in the maize adaptation to nitrate fluctuations. In particular, results obtained suggested that a nitrate depletion might regulate the expression of genes involved in the starvation adaptive response, by affecting the spatio-temporal expression patterns of specific miRNAs.     

miRNAs: Major modulators for crop growth and development under abiotic stresses

Cumulatively, biotic and abiotic stresses of various magnitudes can decrease the production of crops by 70%. miRNAs have emerged as a genetic tool with enormous potential that can be exploited to understand stress tolerance at the molecular level and eventually regulate stress in crops. Plant miRNA targets frequently fit into diverse families of TFs that control the expression of genes related to a certain trait. As key machinery in gene regulatory networks, it is agreed that a broad understanding of miRNAs will greatly increase our understanding of plant responses to environmental stresses. miRNA-led stress regulatory networks are being considered as novel tools for the development of abiotic stress tolerance in crops. At this time, we need to expand our knowledge about the modulatory role of miRNAs during environmental fluctuations. It has become exceedingly clear that with increased understanding of the role of miRNAs during stress, the techniques for using miRNA-mediated gene regulation to enhance plant stress tolerance will become more effective and reliable. In this review we present: (1) miRNAs as a potential avenue for the modulation of abiotic stresses, and (2) summarize the research progress regarding plant responses to stress. Current progress is explained through discussion of the identification and validation of several miRNAs that enhance crop tolerance of salinity, drought, etc., while missing links on different aspects of miRNAs related to abiotic stress tolerance are noted.     

miR398在植物逆境胁迫应答中的作用

MicroRNA (miRNA)是一类新型的调控基因表达的小分子RNA, 它作为基因表达的负调控因子, 在转录后水平调节靶基因的表达。miRNA参与调控植物的生长发育, 并在多种非生物与生物胁迫响应中发挥重要作用。miR398是第一个被报道的受氧化胁迫负调控的miRNA。它通过负调控其靶基因Cu/Zn过氧化物歧化酶(Cu/Zn-superoxide dismutase, CSD)的表达, 在多种逆境胁迫响应中扮演重要角色, 如调节铜代谢平衡, 应答重金属、蔗糖、臭氧等非生物胁迫, 以及参与应答生物胁迫等。文章综述了miR398在多种逆境胁迫响应中重要的调节作用及miR398自身的转录调控。     

Plant microRNAs in molecular breeding

MicroRNAs are small, endogenous, non-coding RNAs found in plants, animals, and in some viruses, which negatively regulate the expression of genes by promoting the degradation of target mRNAs or by translation inhibition. Ever since the discovery of miRNAs, its biology, mechanisms, and functions were extensively studied in the past two decades. Plant and animal miRNAs both regulate target mRNAs, but they differ in scope of complementarity to their target mRNA. Plant microRNAs are known to play essential roles in a wide array of plant development. To date, there are many studies giving evidence that the regulation of miRNA levels can reprogram plant responses to abiotic (physical environment) and biotic stresses (pathogen and herbivore). Most of these studies were first carried out in the model plant Arabidopsis thaliana. Recently, the trend of miRNA research is furthering its role in crop breeding and its evolutionary origin. In this review, we presented the dynamic biogenesis of microRNAs, the diverse functions of miRNAs in plants, and experimental designs used in studying microRNAs in plants, and most importantly, we presented the applications of microRNA-based technology to improve the resistance of crops in abiotic and biotic stresses.     

植物体内调控miRNA合成与功能的机制研究进展

microRNA(miRNA)能够在转录后水平通过剪切或抑制翻译对靶mRNA进行调节,并且广泛参与植物的生长发育、生物胁迫和非生物胁迫等过程,因此引起了众多研究者的关注。随着对miRNA研究的深入,人们发现miRNA从转录到转录后成熟再到行使功能的过程中,会受到很多因子的调控。这些因子可以是蛋白质、核酸序列、基因、甚至miRNA本身,由于这些因子的参与,使得miRNA调节的生物学过程更具复杂性和灵活性。本文从转录、加工、活性调节和反馈调控等层次综述了近年来调控植物miRNA合成与功能方面取得的进展,以期为miRNA调控机制的研究提供理论基础和新思路。     

植物逆境miRNA研究进展

包括生物和非生物在内的多种逆境胁迫是植物正常生长和作物产量提高的重要限制性因素。植物在长期的进化过程中, 通过诱导表达某些抵御或防卫途径的关键基因来实现对胁迫的响应。研究表明, 逆境胁迫不仅会诱导植物蛋白质编码基因的表达, 也会诱导一些非蛋白质编码基因的表达, 这类非蛋白质编码基因的表达产物在植物的生长、发育和应对逆境胁迫等过程中起到重要的调控作用。miRNA(小分子RNA)就是这类非蛋白质编码基因产物中的重要类群, 研究发现, 多种逆境均会诱导miRNA的产生, 其作用是通过引导目的基因mRNA的降解和阻止翻译过程来调控靶基因, 最终通过形态或生理上的变化达到对逆境的适应。文章主要对植物逆境胁迫下miRNA的研究, 特别是逆境胁迫诱导miRNA的产生、靶基因调控以及miRNA在植物适应逆境胁迫过程中的作用进行了综述, 同时, 文章还对在逆境胁迫下植物miRNA的研究方法进行了初步的探讨。     

Identification and characterization of new plant microRNAs using EST analysis

Seventy-five previously known plant microRNAs (miRNAs) were classified into 14 families according to their gene sequence identity. A total of 18,694 plant expressed sequence tags (EST) were found in the GenBank EST databases by comparing all previously known Arabidopsis miRNAs to GenBank‘s plant EST databases with BLAST algorithms. After removing the EST sequences with high numbers (more than 2) of mismatched nucleotides, a total of 812 EST contigs were identified. After predicting and scoring the RNA secondary structure of the 812 EST sequences using mFold software, 338 new potential miRNAs were identified in 60 plant species, miRNAs are widespread. Some microRNAsmay highly conserve in the plant kingdom, and they may have the same ancestor in very early evolution. There is no nucleotide substitution in most miRNAs among many plant species. Some of the new identified potential miRNAs may be induced and regulated by environmental biotic and abiotic stresses. Some may be preferentially expressed in specific tissues, and are regulated by developmental switching. These findings suggest that EST analysis is a good alternative strategy for identifying new miRNA candidates, their targets, and other genes. A large number of miRNAs exist in different plant species and play important roles in plant developmental switching and plant responses to environmental abiotic and biotic stresses as well as signal transduction. Environmental stresses and developmental switching may be the signals for synthesis and regulation of miRNAs in plants. A model for miRNA induction and expression, and gene regulation by miRNA is hypothesized.     

Transgenic approaches for genetic improvement in groundnut (Arachis hypogaea L.) against major biotic and abiotic stress factors

Cultivated groundnut (Arachis hypogaea L.) is considered as one of the primary oilseed crops and a major fodder for cattle industry in most of the developing countries, owing to its rich source of protein. It is due to its geocarpic nature of growth that the overall yield performance of groundnut is hindered by several biotic and abiotic stress factors. Multidimensional attempts were undertaken to combat these factors by developing superior groundnut varieties, modified with integral mechanism of tolerance/resistance; however this approach proved to be futile, owing to inferior pod and kernel quality. As a superior alternative, biotechnological intervention like transformation of foreign genes, either directly (biolistic) or via Agrobacterium, significantly aided in the development of advanced groundnut genotypes equipped with integral resistance against stresses and enhanced yield attributing traits. Several genes triggered by biotic and abiotic stresses, were detected and some of them were cloned and transformed as major parts of transgenic programmes. Application of modern molecular biological techniques, in designing biotic and abiotic stress tolerant/resistant groundnut varieties that exhibited mechanisms of resistance, relied on the expression of specific genes associated to particular stress. The genetically transformed stress tolerant groundnut varieties possess the potential to be employed as donor parents in traditional breeding programmes for developing varieties that are resilient to fungal, bacterial, and viral diseases, as well as to draught and salinity. The present review emphasizes on the retrospect and prospect of genetic transformation tools, implemented for the enhancement of groundnut varieties against key biotic and abiotic stress factors.     

Computational identification of novel family members of microRNA genes in Arabidopsis thaliana and Oryza sativa

MicroRNAs (miRNAs) are a class of endogenous small RNAs that play important regulatory roles in both animals and plants, miRNA genes have been intensively studied in animals, but not in plants. In this study, we adopted a homology search approach to identify homologs of previously validated plant miRNAs in Arabidopsis thaliana and Oryza sativa. We identified 20 potential miRNA genes in Arabidopsis and 40 in O. sativa, providing a relatively complete enumeration of family members for these miRNAs in plants. In addition, a greater number of Arabidopsis miRNAs (MIR168, MIR159 and MIR172) were found to be conserved in rice. With the novel homologs, most of the miRNAs have closely related fellow miRNAs and the number of paralogs varies in the different miRNA families. Moreover, a probable functional segment highly conserved on the elongated stem of pre-miRNA fold-backs of MIR319 and MIR159 family was identified. These results support a model of variegated miRNA regulation in plants, in which miRNAs with different functional elements on their pre-miRNA fold-backs can differ in their function or regulation, and closely related miRNAs can be diverse in their specificity or competence to downregulate target genes. It appears that the sophisticated regulation of miRNAs can achieve complex biological effects through qualitative and quantitative modulation of gene expression profiles in plants.