Llave C, Xie Z, Kasschau KD, Carrington JC. Cleavage of scarecrow-like mRNA targets directed by a class of Arabidopsis miRNA. Science. 2002;297(5589):2053–6. https://doi.org/10.1126/science.1076311.
Article
CAS
PubMed
Google Scholar
Rogers K, Chen X. Biogenesis, turnover, and mode of action of plant microRNAs. Plant Cell. 2013;25(7):2383–99. https://doi.org/10.1105/tpc.113.113159.
Article
CAS
PubMed
PubMed Central
Google Scholar
Yu Y, Jia T, Chen X. The ‘how’ and ‘where’ of plant microRNAs. New Phytol. 2017;216(4):1002–17. https://doi.org/10.1111/nph.14834.
Article
CAS
PubMed
PubMed Central
Google Scholar
Waheed S, Zeng L. The critical role of miRNAs in regulation of flowering time and flower development. Genes (Basel). 2020;11(3). https://doi.org/10.3390/genes11030319.
Li YF, Zheng Y, Addo-Quaye C, Zhang L, Saini A, Jagadeeswaran G, et al. Transcriptome-wide identification of microRNA targets in rice. Plant J. 2010;62(5):742–59. https://doi.org/10.1111/j.1365-313X.2010.04187.x.
Article
CAS
PubMed
Google Scholar
Wang H, Wang H. The miR156/SPL module, a regulatory hub and versatile toolbox, gears up crops for enhanced agronomic traits. Mol Plant. 2015;8(5):677–88. https://doi.org/10.1016/j.molp.2015.01.008.
Article
CAS
PubMed
Google Scholar
Wang L, Zhao J, Zhang M, Li W, Luo K, Lu Z, et al. Identification and characterization of microRNA expression in Ginkgo biloba L. leaves. Tree Genet Genomes. 2015;11(4). https://doi.org/10.1007/s11295-015-0897-3.
Wu G, Poethig RS. Temporal regulation of shoot development in Arabidopsis thaliana by miR156 and its target SPL3. Development. 2006;133(18):3539–47. https://doi.org/10.1242/dev.02521.
Article
CAS
PubMed
Google Scholar
Gao R, Wang Y, Gruber MY, Hannoufa A. miR156/SPL10 modulates lateral root development, branching and leaf morphology in Arabidopsis by silencing AGAMOUS-LIKE 79. Front Plant Sci. 2017;8:2226. https://doi.org/10.3389/fpls.2017.02226.
Article
PubMed
Google Scholar
Poethig RS. Small RNAs and developmental timing in plants. Curr Opin Genet Dev. 2009;19(4):374–8. https://doi.org/10.1016/j.gde.2009.06.001.
Article
CAS
PubMed
PubMed Central
Google Scholar
Wu G, Park MY, Conway SR, Wang JW, Weigel D, Poethig RS. The sequential action of miR156 and miR172 regulates developmental timing in Arabidopsis. Cell. 2009;138(4):750–9. https://doi.org/10.1016/j.cell.2009.06.031.
Article
CAS
PubMed
PubMed Central
Google Scholar
Zhu QH, Helliwell CA. Regulation of flowering time and floral patterning by miR172. J Exp Bot. 2011;62(2):487–95. https://doi.org/10.1093/jxb/erq295.
Article
CAS
PubMed
Google Scholar
Aukerman MJ, Sakai H. Regulation of flowering time and floral organ identity by a microRNA and its APETALA2-like target genes. Plant Cell. 2003;15(11):2730–41. https://doi.org/10.1105/tpc.016238.
Article
CAS
PubMed
PubMed Central
Google Scholar
Murray F, Kalla R, Jacobsen J, Gubler F. A role for HvGAMYB in anther development. Plant J. 2003;33(3):481–91. https://doi.org/10.1046/j.1365-313X.2003.01641.x.
Article
CAS
PubMed
Google Scholar
Kaneko M, Inukai Y, Ueguchi-Tanaka M, Itoh H, Izawa T, Kobayashi Y, et al. Loss-of-function mutations of the rice GAMYB gene impair alpha-amylase expression in aleurone and flower development. Plant Cell. 2004;16(1):33–44. https://doi.org/10.1105/tpc.017327.
Article
CAS
PubMed
PubMed Central
Google Scholar
Wang Y, Sun F, Cao H, Peng H, Ni Z, Sun Q, et al. TamiR159 directed wheat TaGAMYB cleavage and its involvement in anther development and heat response. PLoS One. 2012;7(11):e48445. https://doi.org/10.1371/journal.pone.0048445.
Article
CAS
PubMed
PubMed Central
Google Scholar
Lee H, Yoo SJ, Lee JH, Kim W, Yoo SK, Fitzgerald H, et al. Genetic framework for flowering-time regulation by ambient temperature-responsive miRNAs in Arabidopsis. Nucleic Acids Res. 2010;38(9):3081–93. https://doi.org/10.1093/nar/gkp1240.
Article
CAS
PubMed
PubMed Central
Google Scholar
Kim W, Ahn HJ, Chiou TJ, Ahn JH. The role of the miR399-PHO2 module in the regulation of flowering time in response to different ambient temperatures in Arabidopsis thaliana. Mol Cell. 2011;32(1):83–8. https://doi.org/10.1007/s10059-011-1043-1.
Article
CAS
Google Scholar
Sung S, Amasino RM. Vernalization and epigenetics: how plants remember winter. Curr Opin Plant Biol. 2004;7(1):4–10. https://doi.org/10.1016/j.pbi.2003.11.010.
Article
CAS
PubMed
Google Scholar
Oliver SN, Deng W, Casao MC, Trevaskis B. Low temperatures induce rapid changes in chromatin state and transcript levels of the cereal VERNALIZATION1 gene. J Exp Bot. 2013;64(8):2413–22. https://doi.org/10.1093/jxb/ert095.
Article
CAS
PubMed
PubMed Central
Google Scholar
Yan L, Loukoianov A, Tranquilli G, Helguera M, Fahima T, Dubcovsky J. Positional cloning of the wheat vernalization gene VRN1. Proc Natl Acad Sci. 2003;100(10):6263–8. https://doi.org/10.1073/pnas.0937399100.
Article
CAS
PubMed
PubMed Central
Google Scholar
Danyluk J, Kane NA, Breton G, Limin AE, Fowler DB, Sarhan F. TaVRT-1, a putative transcription factor associated with vegetative to reproductive transition in cereals. Plant Physiol. 2003;132(4):1849–60. https://doi.org/10.1104/pp.103.023523.
Article
CAS
PubMed
PubMed Central
Google Scholar
Xiao J, Xu S, Li C, Xu Y, Xing L, Niu Y, et al. O-GlcNAc-mediated interaction between VER2 and TaGRP2 elicits TaVRN1 mRNA accumulation during vernalization in winter wheat. Nat Commun. 2014;5(1):4572. https://doi.org/10.1038/ncomms5572.
Article
CAS
PubMed
Google Scholar
Yan L, Fu D, Li C, Blechl A, Tranquilli G, Bonafede M, et al. The wheat and barley vernalization gene VRN3 is an orthologue of FT. Proc Natl Acad Sci U S A. 2006;103(51):19581–6. https://doi.org/10.1073/pnas.0607142103.
Article
CAS
PubMed
PubMed Central
Google Scholar
Meng FR, Liu H, Wang KT, Liu LL, Wang SH, Zhao YH, et al. Development-associated microRNAs in grains of wheat (Triticum aestivum L.). BMC Plant Biol. 2013;13(1). https://doi.org/10.1186/1471-2229-13-140.
Wang Y, Shi C, Yang T, Zhao L, Chen J, Zhang N, et al. High-throughput sequencing revealed that microRNAs were involved in the development of superior and inferior grains in bread wheat. Sci Rep. 2018;8(1):13854. https://doi.org/10.1038/s41598-018-31870-z.
Article
CAS
PubMed
PubMed Central
Google Scholar
Li YF, Zheng Y, Jagadeeswaran G, Sunkar R. Characterization of small RNAs and their target genes in wheat seedlings using sequencing-based approaches. Plant Sci. 2013;203-204:17–24. https://doi.org/10.1016/j.plantsci.2012.12.014.
Article
CAS
PubMed
Google Scholar
Wei B, Cai T, Zhang R, Li A, Huo N, Li S, et al. Novel microRNAs uncovered by deep sequencing of small RNA transcriptomes in bread wheat (Triticum aestivum L.) and Brachypodium distachyon (L.) Beauv. Funct Integr Genomics. 2009;9(4):499–511. https://doi.org/10.1007/s10142-009-0128-9.
Article
CAS
PubMed
Google Scholar
De Paola D, Zuluaga DL, Sonnante G. The miRNAome of durum wheat: isolation and characterisation of conserved and novel microRNAs and their target genes. BMC Genomics. 2016;17(1):505. https://doi.org/10.1186/s12864-016-2838-4.
Article
CAS
PubMed
PubMed Central
Google Scholar
Fileccia V, Bertolini E, Ruisi P, Giambalvo D, Frenda AS, Cannarozzi G, et al. Identification and characterization of durum wheat microRNAs in leaf and root tissues. Funct Integr Genomics. 2017;17(5):583–98. https://doi.org/10.1007/s10142-017-0551-2.
Article
CAS
PubMed
Google Scholar
Yao Y, Guo G, Ni Z, Sunkar R, Du J, Zhu JK, et al. Cloning and characterization of microRNAs from wheat (Triticum aestivum L.). Genome Biol. 2007;8(6):R96.
Article
PubMed
PubMed Central
Google Scholar
Li T, Ma L, Geng Y, Hao C, Chen X, Zhang X. Small RNA and Degradome sequencing reveal complex roles of miRNAs and their targets in developing wheat grains. PLoS One. 2015;10(10):e0139658. https://doi.org/10.1371/journal.pone.0139658.
Article
CAS
PubMed
PubMed Central
Google Scholar
Han R, Jian C, Lv J, Yan Y, Chi Q, Li Z, et al. Identification and characterization of microRNAs in the flag leaf and developing seed of wheat (Triticum aestivum L.). BMC Genomics. 2014;15(1):289. https://doi.org/10.1186/1471-2164-15-289.
Article
CAS
PubMed
PubMed Central
Google Scholar
Hou G, Du C, Gao H, Liu S, Sun W, Lu H, et al. Identification of microRNAs in developing wheat grain that are potentially involved in regulating grain characteristics and the response to nitrogen levels. BMC Plant Biol. 2020;20(1):87. https://doi.org/10.1186/s12870-020-2296-7.
Article
CAS
PubMed
PubMed Central
Google Scholar
Song G, Zhang R, Zhang S, Li Y, Gao J, Han X, et al. Response of microRNAs to cold treatment in the young spikes of common wheat. BMC Genomics. 2017;18(1):212. https://doi.org/10.1186/s12864-017-3556-2.
Article
CAS
PubMed
PubMed Central
Google Scholar
Tang Z, Zhang L, Xu C, Yuan S, Zhang F, Zheng Y, et al. Uncovering small RNA-mediated responses to cold stress in a wheat thermosensitive genic male-sterile line by deep sequencing. Plant Physiol. 2012;159(2):721–38. https://doi.org/10.1104/pp.112.196048.
Article
CAS
PubMed
PubMed Central
Google Scholar
Corbesier L, Vincent C, Jang S, Fornara F, Fan Q, Searle I, et al. FT protein movement contributes to long-distance signaling in floral induction of Arabidopsis. Science. 2007;316(5827):1030–3. https://doi.org/10.1126/science.1141752.
Article
CAS
PubMed
Google Scholar
Pearce S, Kippes N, Chen A, Debernardi JM, Dubcovsky J. RNA-seq studies using wheat PHYTOCHROME B and PHYTOCHROME C mutants reveal shared and specific functions in the regulation of flowering and shade-avoidance pathways. BMC Plant Biol. 2016;16(1):141. https://doi.org/10.1186/s12870-016-0831-3.
Article
CAS
PubMed
PubMed Central
Google Scholar
Wu L, Liu D, Wu J, Zhang R, Qin Z, Liu D, et al. Regulation of FLOWERING LOCUS T by a MicroRNA in Brachypodium distachyon. Plant Cell. 2013;25(11):4363–77. https://doi.org/10.1105/tpc.113.118620.
Article
CAS
PubMed
PubMed Central
Google Scholar
Niwa Y, Ito S, Nakamichi N, Mizoguchi T, Niinuma K, Yamashino T, et al. Genetic linkages of the circadian clock-associated genes, TOC1, CCA1 and LHY, in the photoperiodic control of flowering time in Arabidopsis thaliana. Plant Cell Physiol. 2007;48(7):925–37. https://doi.org/10.1093/pcp/pcm067.
Article
CAS
PubMed
Google Scholar
Zhang L, Zheng Y, Jagadeeswaran G, Li Y, Gowdu K, Sunkar R. Identification and temporal expression analysis of conserved and novel microRNAs in Sorghum. Genomics. 2011;98(6):460–8. https://doi.org/10.1016/j.ygeno.2011.08.005.
Article
CAS
PubMed
Google Scholar
Zhao X, Hong P, Wu J, Chen X, Ye X, Pan Y, et al. The tae-miR408-mediated control of TaTOC1 genes transcription is required for the regulation of heading time in wheat. Plant Physiol. 2016;170(3):01216.02015. https://doi.org/10.1104/pp.15.01216.
Article
CAS
Google Scholar
Li YF, Wei K, Wang M, Wang L, Cui J, Zhang D, et al. Identification and temporal expression analysis of conserved and novel microRNAs in the leaves of winter wheat grown in the field. Front Genet. 2019;10:779. https://doi.org/10.3389/fgene.2019.00779.
Article
CAS
PubMed
PubMed Central
Google Scholar
Sun F, Guo G, Du J, Guo W, Peng H, Ni Z, et al. Whole-genome discovery of miRNAs and their targets in wheat ( Triticum aestivum L.). BMC Plant Biol. 2014;14(1):142.
Article
PubMed
PubMed Central
Google Scholar
Shevtsov S, Nevo-Dinur K, Faigon L, Sultan LD, Zmudjak M, Markovits M, et al. Control of organelle gene expression by the mitochondrial transcription termination factor mTERF22 in Arabidopsis thaliana plants. PLoS One. 2018;13(7):e0201631. https://doi.org/10.1371/journal.pone.0201631.
Article
CAS
PubMed
PubMed Central
Google Scholar
Zhang L, Hou D, Chen X, Li D, Zhu L, Zhang Y, et al. Exogenous plant MIR168a specifically targets mammalian LDLRAP1: evidence of cross-kingdom regulation by microRNA. Cell Res. 2012;22(1):107–26. https://doi.org/10.1038/cr.2011.158.
Article
CAS
PubMed
Google Scholar
Sunkar R, Kapoor A, Zhu J-K. Posttranscriptional induction of two cu/Zn superoxide dismutase genes in Arabidopsis is mediated by downregulation of miR398 and important for oxidative stress tolerance. Plant Cell. 2006;18(8):2051–65. https://doi.org/10.1105/tpc.106.041673.
Article
CAS
PubMed
PubMed Central
Google Scholar
Sunkar R, Zhu J-K. Novel and stress-regulated microRNAs and other small RNAs from Arabidopsis. Plant Cell. 2004;16(8):2001–19. https://doi.org/10.1105/tpc.104.022830.
Article
CAS
PubMed
PubMed Central
Google Scholar
Megha S, Basu U, Kav NNV. Regulation of low temperature stress in plants by microRNAs. Plant Cell Environ. 2018;41(1):1–15. https://doi.org/10.1111/pce.12956.
Article
CAS
PubMed
Google Scholar
Schommer C, Bresso EG, Spinelli SV, Palatnik JF. Role of MicroRNA miR319 in plant development. Signal Commun Plants. 2012;15:29–47. https://doi.org/10.1007/978-3-642-27384-1_2.
Article
Google Scholar
Achard P, Herr A, Baulcombe DC, Harberd NP. Modulation of floral development by a gibberellin-regulated microRNA. Development. 2004;131(14):3357–65. https://doi.org/10.1242/dev.01206.
Article
CAS
PubMed
Google Scholar
Fahlgren N, Montgomery TA, Howell MD, Allen E, Dvorak SK, Alexander AL, et al. Regulation of AUXIN RESPONSE FACTOR3 by TAS3 ta-siRNA affects developmental timing and patterning in Arabidopsis. Curr Biol. 2006;16(9):939–44. https://doi.org/10.1016/j.cub.2006.03.065.
Article
CAS
PubMed
Google Scholar
Garcia D. A miRacle in plant development: role of microRNAs in cell differentiation and patterning. Semin Cell Dev Biol. 2008;19(6):586–95. https://doi.org/10.1016/j.semcdb.2008.07.013.
Article
CAS
PubMed
Google Scholar
Rubio-Somoza I, Weigel D. MicroRNA networks and developmental plasticity in plants. Trends Plant Sci. 2011;16(5):258–64. https://doi.org/10.1016/j.tplants.2011.03.001.
Article
CAS
PubMed
Google Scholar
Ru P, Xu L, Ma H, Huang H. Plant fertility defects induced by the enhanced expression of microRNA167. Cell Res. 2006;16(5):457–65. https://doi.org/10.1038/sj.cr.7310057.
Article
CAS
PubMed
Google Scholar
Liu X, Huang J, Wang Y, Khanna K, Xie Z, Owen HA, et al. The role of floral organs in carpels, an Arabidopsis loss-of-function mutation in MicroRNA160a, in organogenesis and the mechanism regulating its expression. Plant J. 2010;62(3):416–28. https://doi.org/10.1111/j.1365-313X.2010.04164.x.
Article
CAS
PubMed
Google Scholar
Galluzzi L, Kepp O, Kroemer G. Mitochondria: master regulators of danger signalling. Nat Rev Mol Cell Biol. 2012;13(12):780–8. https://doi.org/10.1038/nrm3479.
Article
CAS
PubMed
Google Scholar
Kazama T, Nakamura T, Watanabe M, Sugita M, Toriyama K. Suppression mechanism of mitochondrial ORF79 accumulation by Rf1 protein in BT-type cytoplasmic male sterile rice. Plant J. 2008;55(4):619–28. https://doi.org/10.1111/j.1365-313X.2008.03529.x.
Article
CAS
PubMed
Google Scholar
Akagi H, Nakamura A, Yokozeki-Misono Y, Inagaki A, Takahashi H, Mori K, et al. Positional cloning of the rice Rf-1 gene, a restorer of BT-type cytoplasmic male sterility that encodes a mitochondria-targeting PPR protein. Theor Appl Genet. 2004;108(8):1449–57. https://doi.org/10.1007/s00122-004-1591-2.
Article
CAS
PubMed
Google Scholar
Bentolila S, Alfonso A, Hanson M. A pentatricopeptide repeat-containing gene restores fertility to cytoplasmic male-sterile plants. Proc Natl Acad Sci U S A. 2002;99(16):10887–92. https://doi.org/10.1073/pnas.102301599.
Article
CAS
PubMed
PubMed Central
Google Scholar
Brown GG, Formanova N, Jin H, Wargachuk R, Dendy C, Patil P, et al. The radish Rfo restorer gene of Ogura cytoplasmic male sterility encodes a protein with multiple pentatricopeptide repeats. Plant J. 2003;35(2):262–72. https://doi.org/10.1046/j.1365-313X.2003.01799.x.
Article
CAS
PubMed
Google Scholar
Kazama T, Toriyama K. A pentatricopeptide repeat-containing gene that promotes the processing of aberrant atp6 RNA of cytoplasmic male-sterile rice. FEBS Lett. 2003;544(1–3):99–102. https://doi.org/10.1016/S0014-5793(03)00480-0.
Article
CAS
PubMed
Google Scholar
Nakamura T, Meierhoff K, Westhoff P, Schuster G. RNA-binding properties of HCF152, an Arabidopsis PPR protein involved in the processing of chloroplast RNA. Eur J Biochem. 2003;270(20):4070–81. https://doi.org/10.1046/j.1432-1033.2003.03796.x.
Article
CAS
PubMed
Google Scholar
Ikeda TM, Gray MW. Characterization of a DNA-binding protein implicated in transcription in wheat mitochondria. Mol Cell Biol. 1999;19(12):8113–22. https://doi.org/10.1128/MCB.19.12.8113.
Article
CAS
PubMed
PubMed Central
Google Scholar
Lahmy S, Barneche F, Derancourt J, Filipowicz W, Delseny M, Echeverria M. A chloroplastic RNA-binding protein is a new member of the PPR family. FEBS Lett. 2000;480(2–3):255–60. https://doi.org/10.1016/S0014-5793(00)01935-9.
Article
CAS
PubMed
Google Scholar
Samad AFA, Rahnamaie-Tajadod R, Sajad M, Jani J, Murad AMA, Noor NM, et al. Regulation of terpenoid biosynthesis by miRNA in Persicaria minor induced by Fusarium oxysporum. BMC Genomics. 2019;20(1):586. https://doi.org/10.1186/s12864-019-5954-0.
Article
CAS
PubMed
PubMed Central
Google Scholar
Zhao S, Wang X, Yan X, Guo L, Mi X, Xu Q, et al. Revealing of microRNA involved regulatory gene networks on Terpenoid biosynthesis in Camellia sinensis in different growing time points. J Agric Food Chem. 2018;66(47):12604–16. https://doi.org/10.1021/acs.jafc.8b05345.
Article
CAS
PubMed
Google Scholar
Ganguly A, Dixit R. Mechanisms for regulation of plant kinesins. Curr Opin Plant Biol. 2013;16(6):704–9. https://doi.org/10.1016/j.pbi.2013.09.003.
Article
CAS
PubMed
Google Scholar
Zhu C, Dixit R. Functions of the Arabidopsis kinesin superfamily of microtubule-based motor proteins. Protoplasma. 2012;249(4):887–99. https://doi.org/10.1007/s00709-011-0343-9.
Article
CAS
PubMed
Google Scholar
Zhang M, Zhang B, Qian Q, Yu Y, Li R, Zhang J, et al. Brittle Culm 12, a dual-targeting kinesin-4 protein, controls cell-cycle progression and wall properties in rice. Plant J. 2010;63(2):312–28. https://doi.org/10.1111/j.1365-313X.2010.04238.x.
Article
CAS
PubMed
PubMed Central
Google Scholar
Li J, Jiang J, Qian Q, Xu Y, Zhang C, Xiao J, et al. Mutation of rice BC12/GDD1, which encodes a kinesin-like protein that binds to a GA biosynthesis gene promoter, leads to dwarfism with impaired cell elongation. Plant Cell. 2011;23(2):628–40. https://doi.org/10.1105/tpc.110.081901.
Article
CAS
PubMed
PubMed Central
Google Scholar
Wahl V, Brand LH, Guo Y-L, Schmid M. The FANTASTIC FOUR proteins influence shoot meristem size in Arabidopsis thaliana. BMC Plant Biol. 2010;10(1). https://doi.org/10.1186/1471-2229-10-285.
Fu XY, Li CH, Zhao YK, Shi ZL, Guo JK, He MQ. Analysis of high-yield, stability and adaptation of new wheat variety ‘Shimai22’. Chin Agric Sci Bull. 2016;32(21):38–43.
Google Scholar
Jagadeeswaran G, Nimmakayala P, Zheng Y, Gowdu K, Reddy UK, Sunkar R. Characterization of the small RNA component of leaves and fruits from four different cucurbit species. BMC Genomics. 2012;13(1):329. https://doi.org/10.1186/1471-2164-13-329.
Article
CAS
PubMed
PubMed Central
Google Scholar
Zheng Y, Li T, Xu Z, Wai CM, Chen K, Zhang X, et al. Identification of microRNAs, phasiRNAs and their targets in pineapple. Trop Plant Biol. 2016;9(3):176–86. https://doi.org/10.1007/s12042-016-9173-4.
Article
CAS
Google Scholar
Li RQ, Yu C, Li YR, Lam TW, Yiu SM, Kristiansen K, et al. SOAP2: an improved ultrafast tool for short read alignment. Bioinformatics. 2009;25(15):1966–7. https://doi.org/10.1093/bioinformatics/btp336.
Article
CAS
PubMed
Google Scholar
Zuker M. Mfold web server for nucleic acid folding and hybridization prediction. Nucleic Acids Res. 2003;31(13):3406–15. https://doi.org/10.1093/nar/gkg595.
Article
CAS
PubMed
PubMed Central
Google Scholar
Wang L, Feng Z, Wang X, Wang X, Zhang X. DEGseq: an R package for identifying differentially expressed genes from RNA-seq data. Bioinformatics. 2010;26(1):136–8. https://doi.org/10.1093/bioinformatics/btp612.
Article
CAS
PubMed
Google Scholar
Livak KJ, Schmittgen TD. Analysis of relative gene expression data using real-time quantitative PCR and the 2(−Delta Delta C(T)) method. Methods. 2001;25(4):402–8. https://doi.org/10.1006/meth.2001.1262.
Article
CAS
PubMed
Google Scholar