Intergenic transformation of AtMYB44 confers drought stress tolerance in rice seedlings

Abstract

We transformed rice (Oryza sativa L. Japonica cv. Ilmi) calli with the Arabidopsis transcription factor gene AtMYB44 using Agrobacterium-mediated transformation. The T-DNA construct to be transformed contained tflA cDNA (encoding a toxoflavin lyase) as a selectable marker. Since toxoflavin is a photosensitizing phytotoxin, transgenic plantlets were selected based on their capacity for root development on medium containing this toxin in the light. Homozygous lines were selected by determining the segregation patterns, expression levels, and copy numbers of AtMYB44. Intergenic genomic locations of the inserted T-DNA in the three transgenic lines were confirmed by adaptor-ligation polymerase chain reaction and analysis using FSTVAL ( http://bioinfo.mju.ac.kr/fstval/ ), an open-access web tool used to localize the flanking sequences of the transgene. Drought tolerance of young seedlings of the transgenic lines was determined based on the recovery of wilted leaves by re-watering after 3 days of water deprivation in a 105-well (35W × 35L × 45D mm/per well) plate. The three transgenic lines showed average survival rates of 80.4, 93.5, and 72.6%, respectively, whereas wild-type plants failed to recover after re-watering. Thus, the transgenic rice plants exhibited significantly enhanced tolerance to drought stress, as was shown previously in AtMYB44-overexpressing transgenic Arabidopsis and soybean. These results suggest that AtMYB44 activates a drought tolerance mechanism that is conserved in both monocotyledonous and dicotyledonous plants.