Development of flooding-tolerant Arabidopsis thaliana by autoregulated cytokinin production

Flooding is one of the most serious environmental stresses that affect plan t growth and productivity. Flooding causes premature senescence which resul ts in leaf chlorosis, necrosis, defoliation, cessation of growth and reduce d yield. This study was conducted to determine the effects of autoregulated cytokinin production on the flooding tolerance of Arabidopsis thaliana pla nts. 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 infiltr ation. Four transgenic lines were chosen for flooding tolerance determinati ons. DNA hybridization analysis and PCR confirmed that all four of the tran sgenic lines carried the ipt gene. The segregation of kanamycin resistance in the T-2 generation indicated 1 to 3 integration events. GUS expression a nd RT-PCR of the ipt gene confirmed the senescence-specificity of the SAG12 promoter. Morphologically, the transgenic lines appeared healthy and norma l. 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 submergenc e was assayed in three independent experiments. All four transgenic lines w ere consistently more tolerant to flooding than wild-type plants. The resul ts indicated that endogenously produced cytokinin can regulate senescence c aused by flooding stress, thereby, increasing plant tolerance to flooding. This study provides a novel mechanism to improve flooding tolerance in plan ts.