[1] Jones-Rhoades MW, Bartel DP, Bartel B. MicroRNAs and their regulatory roles in plants. Annu Rev Plant Biol, 2006, 57(1): 19–53.<\p>

[2] Chen XM. Small RNAs and their roles in plant development. Annu Rev Cell Dev Biol, 2009, 25(1): 21–44.<\p>

[3] Shukla LI, Chinnusamy V, Sunkar R. The role of microRNAs and other endogenous small RNAs in plant stress responses. Biochim Biophys Acta, 2008, 1779(11): 743–748.<\p>

[4] Ruiz-Ferrer V, Voinnet O. Roles of plant small RNAs in biotic stress responses. Annu Rev Plant Biol, 2009, 60(1): 485–510.<\p>

[5] Tuskan GA, DiFazio S, Jansson S, Bohlmann J, Grigoriev I, Hellsten U. The genome of black cottonwood, Populus trichocarpa (Torr. & Gray). Science, 2006, 313(5793): 1596–1604.<\p>

[6] Yang XH, Kalluri UC, DiFazio SP, Wullschleger SD, Tschaplinski TJ, Cheng ZM, Tuskan GA. Poplar genomics: state of the science. Crit Rev Plant Sci, 2009, 28(5): 285– 308.<\p>

[7] Taylor G. Populus: Arabidopsis for forestry. Do we need a model tree? Ann Bot, 2002, 90(6): 681–689.<\p>

[8] Jansson S, Douglas CJ. Populus: A model system for plant biology. Annu Rev Plant Biol, 2007, 58(1): 435–458.<\p>

[9] Lu SF, Sun YH, Chiang VL. Stress-responsive microRNAs in Populus. Plant J, 2008, 55(1): 131–151.<\p>

[10] Lu SF, Sun YH, Shi R, Clark C, Li L, Chiang VL. Novel and mechanical stress-responsive MicroRNAs in Populus trichocarpa that are absent from Arabidopsis. Plant Cell, 2005, 17(8): 2186–2203.<\p>

[11] Puzey JR, Karger A, Axtell M, Kramer EM. Deep annotation of Populus trichocarpa microRNAs from diverse tissue sets. PLoS ONE, 2012, 7(3): e33034.<\p>

[12] 魏强, 梁永宏, 李广林. 植物miRNA的进化. 遗传, 2013, 25(3): 315–323.<\p>

[13] Li AL, Mao L. Evolution of plant microRNA gene families. Cell Res, 2007, 17(3): 212–218.<\p>

[14] Kozomara A, Griffiths-Jones S. miRBase: integrating microRNA annotation and deep-sequencing data. Nucleic Acids Res, 2011, 39(Suppl. 1): D152–D157.<\p>

[15] Maher C, Stein L, Ware D. Evolution of Arabidopsis microRNA families through duplication events. Genome Res, 2006, 16(4): 510–519.<\p>

[16] Zhang Z, Li J, Zhao X-Q, Wang J, Wong GK-S, Yu J. KaKs_Calculator: calculating Ka and Ks through model selection and model averaging. Geno Prot Bioinfo, 2006, 4(4): 259–263.<\p>

[17] Yang Z, Nielsen R. Estimating synonymous and nonsynonymous substitution rates under realistic evolutionary models. Mol Biol Evol, 2000, 17(1): 32–43.<\p>

[18] Blanc G, Wolfe KH. Widespread paleopolyploidy in model plant species inferred from age distributions of duplicate genes. Plant Cell, 2004, 16(7): 1667–1678.<\p>

[19] Lynch M, Conery JS. The evolutionary fate and consequences of duplicate genes. Science, 2000, 290(5494): 1151–1155.<\p>

[20] Koch MA, Haubold B, Mitchell-Olds T. Comparative evolutionary analysis of chalcone synthase and alcohol dehydrogenase loci in Arabidopsis, Arabis, and related genera (Brassicaceae). Mol Biol Evol, 2000, 17(10): 1483– 1498.<\p>

[21] Li B, Qin Y, Duan H, Yin W, Xia X. Genome-wide characterization of new and drought stress responsive microRNAs in Populus euphratica. J Exp Bot, 2011, 62(11): 3765–3779.<\p>

[22] Wan LC, Zhang HY, Lu SF, Zhang L, Qiu ZB, Zhao YY, Zeng QY, Lin JX. Transcriptome-wide identification and characterization of miRNAs from Pinus densata. BMC Genomics, 2012, 13(1): 132.<\p>

[23] 方炎明. 陆地植物新系统树之诠释与简评. 南京林业大学学报 (自然科学版), 2009, 33(4): 1–7.<\p>

[24] Sterck L, Rombauts S, Jansson S, Sterky F, Rouze P, Van de Peer Y. EST data suggest that poplar is an ancient polyploid. New Phytol, 2005, 167(1): 165–170.<\p>

[25] F