Isolation And Identification Of Cold-tolerance And Drought-resistance Related MicroRNA In Cassava And Other Euphorbiaceae

MicroRNA(miRNA) is a class of～21nt non-coding RNAs that regulate mRNAs at the post-transcriptional level,miRNAs are key regulators of nearly all essential biological processes.Aiming at understanding miRNAs' functions in Euphorbiaceae, a large flowering plant family,we performed a genome-scale systematic study of miRNAs in Euphorbiaceae,by combining computational prediction and experimental analysis to overcome the difficulty of lack of genomes for most Euphorbiaceous species.Specifically,we predicted 85 conserved miRNAs of 23 miRNA families in Castor bean,and then experimentally verified and characterized 58(68.2%) of the 85 miRNAs in at least one of four agri-economically important Euphorbiaceous species, Castor bean(Ricinus communis),Cassava(Manihot esculenta),Rubber tree(Hevea brasiliensis),and Jatropha(Jatropha cureas),during normal seedling development. To elucidate their functions in stress response,we further verified and profiled 48 (56.5%) of the 85 miRNAs under cold and drought stresses as well as during the processes of stress recovery.The results revealed speciesandcondition-specific miRNA expression patterns.Finally,we predicted 258 miRNA:target binding partners, and identified the cleavage sites of six out of ten miRNA targets by modified 5' RACE.This study produced the first collection of miRNAs and their targets in Euphorbiaceae.Our results revealed wide conservation of many miRNAs and their diverse functions in Euphorbiaceous plants during seedling growth and in response to abiotic stresses.