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microRNAs (miRNAs) are a class of single-stranded endogenous non-coding RNAs that play critical roles in plant growth, development, and environmental stress responses. Temperature is one of the major physical parameters disturbing cellular homeostasis and causing leaf etiolation in plants. Previous studies have reported that several conserved and novel miRNAs were responsive to heat stress in plants. However, the characterization of miRNAs responsive to heat stress in radish remains poorly understood. To better understand miRNAs and their target genes under heat stress, two small RNA libraries were constructed from heat-treated (Heat24) and heat-untreated (CK) radish roots. Using Solexa system, totally, 26 known and 19 novel miRNAs were identified as differentially expressed under heat stress. Expression patterns of a set of heat-responsive miRNAs were validated by quantitative real-time PCR (qRT-PCR). Furthermore, 422 sliced targets for 25 known miRNAs were identified by degradome sequencing technology, and most of the identified targets are involved in multiple biological processes including transcriptional regulation and response to biotic and abiotic stresses. Moreover, some miRNAs and their corresponding targets, which are related to the accumulation of heat stress transcription factors and heat shock proteins, played important roles in thermo-tolerance in radish. These findings could enhance the understanding of molecular mechanisms underlying miRNAs and their targets in regulating plant responses to heat stress. [ABSTRACT FROM AUTHOR]

microRNAs (miRNAs), endogenous non-coding RNAs of approximately 21-24 nucleotides, are important regulators of transcriptional and post-transcriptional gene expression. These regulators play a key role during plant growth and development, including embryogenesis, which is crucial to the life cycle of most plant species. However, although embryogenesis-associated miRNAs have been isolated in a few species, the diversity of these regulatory miRNAs remains largely unexplored, especially in radish. In this study, two small RNA libraries were constructed from radish ovules before and after fertilization. Both libraries were sequenced by next generation sequencing (NGS) technology. This analysis identified 144 conserved and 34 non-conserved miRNAs (representing 43 known miRNA families) and 38 novel miRNAs (representing 28 miRNA families). Comparative analysis revealed that 29 known and 10 novel miRNA families were differentially expressed during embryogenesis. QRT-PCR analysis confirmed miRNA expression patterns and revealed tissue-specific and/or developmental stage-dependent expression for some miRNAs. Moreover, potential target predictions indicated that most of these targets were transcription factors involved in regulating plant growth, development and metabolism. Notably, target transcripts such as squamosa promoter-binding protein, auxin response factor and agamous-like MADS-box protein participated in radish embryogenesis. [ABSTRACT FROM AUTHOR]

MicroRNAs (miRNAs) are small noncoding RNAs that play pivotal roles in plant growth, development and stress response. Chromium (Cr) is one of common environmental contaminants possessing potential health hazards to living organisms. To date, little is known about the regulatory roles of miRNAs in response to Cr stress in radish. To systematically identify Cr-responsive miRNAs and their targets in radish, two sRNA libraries derived from Cr-free (CK) and Cr-treated (Cr200) roots were constructed. With Solexa sequencing, 81 known and 72 novel miRNAs were identified, from which 54 known and 16 novel miRNAs were significantly differentially expressed under Cr stress. Several target genes for Cr-responsive miRNAs encode different transcription factor (TF) families, including SPLs, MYBs, ERFs and bZIPs, might regulate corresponding HM-related transcriptional processes in plants. Notably, a few key responsive enzymes or proteins, including HMA, YSL1 and ABC transporter protein were involved in Cr uptake and homeostasis process. Furthermore, the expression patterns of some Cr-responsive miRNAs and their targets were validated by RT-qPCR. This study represents the first characterization of Cr-responsive miRNAs and their targets in radish. The outcomes of this study could provide novel insights into miRNA-mediated regulatory mechanisms underlying plant response to Cr stress in root vegetable crops. [ABSTRACT FROM AUTHOR]