A method of increasing tolerance of a plant to an abiotic stress or increasing biomass, vigor or yield of a plant is disclosed. The method comprising upregulating within the plant an exogenous polynucleotide of a microRNA or a precursor thereof, wherein the microRNA is selected from the group consisting of miR-156, miR-169, miR-164, miR-159, miR-167, miR-529, miR-168, ppt-miR395, sof-miR408a, ath-miR408, miR-1039, miR-1091, miR-1118, miR-1134 and miR-1129, thereby increasing the tolerance of the plant to the abiotic stress or increasing the biomass, vigor or yield of the plant.
