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Pollen development is an important and complex biological process in the sexual reproduction of flowering plants. Although the cytological characteristics of pollen development are well defined, the regulation of its early stages remains largely unknown. In the present study, miRNAs were explored in the early development of broccoli (Brassica oleracea var. italica) pollen. A total of 333 known miRNAs that originated from 235 miRNA families were detected. Fifty-five novel miRNA candidates were identified. Sixty of the 333 known miRNAs and 49 of the 55 predicted novel miRNAs exhibited significantly differential expression profiling in the three distinct developmental stages of broccoli pollen. Among these differentially expressed miRNAs, miRNAs that would be involved in the developmental phase transition from uninucleate microspores to binucleate pollen grains or frombinucleate to trinucleate pollen grains were identified.miRNAs that showed significantly enriched expression in a specific early stage of broccoli pollen development were also observed. In addition, 552 targets for 127 knownmiRNAs and 69 targets for 40 predicted novel miRNAs were bioinformatically identified. Functional annotation and GO (Gene Ontology) analysis indicated that the putative miRNA targets showed significant enrichment in GO terms that were related to plant organ formation and morphogenesis. Some of enriched GO terms were detected for the targets directly involved in plant male reproduction development. These findings provided new insights into the functions of miRNA-mediated regulatory networks in broccoli pollen development. [ABSTRACT FROM AUTHOR]

Dehydration responsive element binding proteins are transcription factors of the plant-specific AP2 family, many of which contribute to abiotic stress responses in several plant species. We investigated the possibility of increasing drought tolerance in the traditional Chinese medicinal herb, Salvia miltiorrhiza, through modulating the transcriptional regulation of AtDREB1C in transgenic plants under the control of a constitutive (35S) or drought-inducible (RD29A) promoter. AtDREB1C transgenic S. miltiorrhiza plants showed increased survival under severe drought conditions compared to the non-transgenic wild-type (WT) control. However, transgenic plants with constitutive overexpression of AtDREB1C showed considerable dwarfing relative to WT. Physiological tests suggested that the higher chlorophyll content, photosynthetic capacity, and superoxide dismutase, peroxidase, and catalase activity in the transgenic plants enhanced plant drought stress resistance compared to WT. Transcriptome analysis of S. miltiorrhiza following drought stress identified a number of differentially expressed genes (DEGs) between the AtDREB1C transgenic lines and WT. These DEGs are involved in photosynthesis, plant hormone signal transduction, phenylpropanoid biosynthesis, ribosome, starch and sucrose metabolism, and other metabolic pathways. The modified pathways involved in plant hormone signaling are thought to be one of the main causes of the increased drought tolerance of AtDREB1C transgenic S. miltiorrhiza plants. [ABSTRACT FROM AUTHOR]

Drought decreases crop productivity more than any other type of environmental stress. Transcription factors (TFs) play crucial roles in regulating plant abiotic stress responses. The Arabidopsis thaliana gene DREB1A/CBF3, encoding a stress-inducible TF, was introduced into Salvia miltiorrhiza. Ectopic expression of AtDREB1A resulted in increased drought tolerance, and transgenic lines had higher relative water content and Chl content, and exhibited an increased photosynthetic rate when subjected to drought stress. AtDREB1A transgenic plants generally displayed lower malondialdehyde (MDA), but higher superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD) activities under drought stress. In particular, plants with ectopic AtDREB1A expression under the control of the stressinduced RD29A promoter exhibited more tolerance to drought compared with p35S::AtDREB1A transgenic plants, without growth inhibition or phenotypic aberrations. Differential gene expression profiling of wild-type and pRD29A::AtDREB1A transgenic plants following drought stress revealed that the expression levels of various genes associated with the stress response, photosynthesis, signaling, carbohydrate metabolism and protein protection were substantially higher in transgenic plants. In addition, the amount of salvianolic acids and tanshinones was significantly elevated in AtDREB1A transgenic S. miltiorrhiza roots, and most of the genes in the related biosynthetic pathways were up-regulated. Together, these results demonstrated that inducing the expression of a TF can effectively regulate multiple genes in the stress response pathways and significantly improve the resistance of plants to abiotic stresses. Our results also suggest that genetic manipulation of a TF can improve production of valuable secondary metabolites by regulating genes in associated pathways. [ABSTRACT FROM AUTHOR]