title: Boron-deficiency-responsive microRNAs and their targets in Citrus sinensis leaves.
abstract: BACKGROUND
  MicroRNAs play important roles in the adaptive responses of plants to nutrient deficiencies. Most research, however, has focused on nitrogen (N), phosphorus (P), sulfur (S), copper (Cu) and iron (Fe) deficiencies, limited data are available on the differential expression of miRNAs and their target genes in response to deficiencies of other nutrient elements. In this study, we identified the known and novel miRNAs as well as the boron (B)-deficiency-responsive miRNAs from citrus leaves in order to obtain the potential miRNAs related to the tolerance of citrus to B-deficiency.
  
  
  METHODS
  Seedlings of 'Xuegan' [Citrus sinensis (L.) Osbeck] were supplied every other day with B-deficient (0 μM H3BO3) or -sufficient (10 μM H3BO3) nutrient solution for 15 weeks. Thereafter, we sequenced two small RNA libraries from B-deficient and -sufficient (control) citrus leaves, respectively, using Illumina sequencing.
  
  
  RESULTS
  Ninety one (83 known and 8 novel) up- and 81 (75 known and 6 novel) down-regulated miRNAs were isolated from B-deficient leaves. The great alteration of miRNA expression might contribute to the tolerance of citrus to B-deficiency. The adaptive responses of miRNAs to B-deficiency might related to several aspects: (a) attenuation of plant growth and development by repressing auxin signaling due to decreased TIR1 level and ARF-mediated gene expression by altering the expression of miR393, miR160 and miR3946; (b) maintaining leaf phenotype and enhancing the stress tolerance by up-regulating NACs targeted by miR159, miR782, miR3946 and miR7539; (c) activation of the stress responses and antioxidant system through down-regulating the expression of miR164, miR6260, miR5929, miR6214, miR3946 and miR3446; (d) decreasing the expression of major facilitator superfamily protein genes targeted by miR5037, thus lowering B export from plants. Also, B-deficiency-induced down-regulation of miR408 might play a role in plant tolerance to B-deficiency by regulating Cu homeostasis and enhancing superoxide dismutase activity.
  
  
  CONCLUSIONS
  Our study reveals some novel responses of citrus to B-deficiency, which increase our understanding of the adaptive mechanisms of citrus to B-deficiency at the miRNA (post-transcriptional) level.
authors.affiliation: College of Resource and Environmental Science, Fujian Agriculture and Forestry University, Fuzhou, 350002, China.|Institute of Horticultural Plant Physiology, Biochemistry and Molecular Biology, Fujian Agriculture and Forestry University, Fuzhou, 350002, China.
authors.forename: Yi-Bin
authors.initials: YB
authors.lastname: Lu
authors.affiliation: Institute of Materia Medica, Fujian Academy of Medical Sciences, Fuzhou, 350001, China. qiyiping2008@hotmail.com.
authors.forename: Yi-Ping
authors.initials: YP
authors.lastname: Qi
authors.affiliation: College of Resource and Environmental Science, Fujian Agriculture and Forestry University, Fuzhou, 350002, China. talstoy@sina.com.|Institute of Horticultural Plant Physiology, Biochemistry and Molecular Biology, Fujian Agriculture and Forestry University, Fuzhou, 350002, China. talstoy@sina.com.
authors.forename: Lin-Tong
authors.initials: LT
authors.lastname: Yang
authors.affiliation: College of Resource and Environmental Science, Fujian Agriculture and Forestry University, Fuzhou, 350002, China. 6253730@163.com.|Institute of Horticultural Plant Physiology, Biochemistry and Molecular Biology, Fujian Agriculture and Forestry University, Fuzhou, 350002, China. 6253730@163.com.
authors.forename: Peng
authors.initials: P
authors.lastname: Guo
authors.affiliation: College of Resource and Environmental Science, Fujian Agriculture and Forestry University, Fuzhou, 350002, China. fauliyan@163.com.
authors.forename: Yan
authors.initials: Y
authors.lastname: Li
authors.affiliation: College of Resource and Environmental Science, Fujian Agriculture and Forestry University, Fuzhou, 350002, China. lisongchen2002@hotmail.com.|Institute of Horticultural Plant Physiology, Biochemistry and Molecular Biology, Fujian Agriculture and Forestry University, Fuzhou, 350002, China. lisongchen2002@hotmail.com.|The Higher Educational Key Laboratory of Fujian Province for Soil Ecosystem Health and Regulation, Fujian Agriculture and Forestry University, Fuzhou, 350002, China. lisongchen2002@hotmail.com.|Fujian Key Laboratory for Plant Molecular and Cell Biology, Fujian Agriculture and Forestry University, Fuzhou, 350002, China. lisongchen2002@hotmail.com.
authors.forename: Li-Song
authors.initials: LS
authors.lastname: Chen
mesh_terms: D001895:Boron / Q000172:deficiency*; D032084:Citrus sinensis / Q000235:genetics* / Q000378:metabolism; D035683:MicroRNAs / Q000235:genetics* / Q000378:metabolism; D018515:Plant Leaves / Q000235:genetics / Q000378:metabolism; D018749:RNA, Plant / Q000235:genetics* / Q000378:metabolism
chemical_list: D035683:MicroRNAs; D018749:RNA, Plant; D001895:Boron