Development of flooding-tolerant Arabidopsis thaliana by autoregulated cytokinin production

Flooding is one of the most serious environmental stresses that affect plant growth and productivity. Flooding causes premature senescence which results in leaf chlorosis, necrosis, defoliation, cessation of growth and reduced yield. This study was conducted to determine the effects of autoregulated cytokinin production on the flooding tolerance of Arabidopsis thaliana plants. A chimeric gene containing the senescence-specific SAG12 promoter and the ipt gene coding for isopentenyl transferase, a rate-limiting enzyme in the cytokinin biosynthesis pathway, was constructed. The chimeric gene was introduced into Arabidopsis plants by Agrobacterium-mediated vacuum infiltration. Four transgenic lines were chosen for flooding tolerance determinations. DNA hybridization analysis and PCR confirmed that all four of the transgenic lines carried the ipt gene. The segregation of kanamycin resistance in the T-2 generation indicated 1 to 3 integration events. GUS expression and RT-PCR of the ipt gene confirmed the senescence-specificity of the SAG12 promoter. Morphologically, the transgenic lines appeared healthy and normal. Transgenic plants began to flower at the same time as wild-type plants, but the period from flowering to senescence was lengthened by 7 to 12 days. Tolerance of the transgenic plants to waterlogging and complete submergence was assayed in three independent experiments. All four transgenic lines were consistently more tolerant to flooding than wild-type plants. The results indicated that endogenously produced cytokinin can regulate senescence caused by flooding stress, thereby, increasing plant tolerance to flooding. This study provides a novel mechanism to improve flooding tolerance in plants.