Down-regulation of S-adenosylmethionine decarboxylase genes results in reduced plant length, pollen viability, and abiotic stress tolerance

S-adenosylmethionine decarboxylase (SAMDC) is a key enzyme for synthesis of polyamines, regulating plant growth and development as well as plant stress responses. Transgenic rice plants down-regulating OsSAMDC2 were generated by RNA interference. Transcript levels of OsSAMDC2, OsSAMDC1 and OsSAMDC4 were all reduced in transgenic rice, along with decreased levels of sperimidine (Spd) and spermin (Spm) and polyamine oxidase activity. The transgenic lines showed a reduced apical dominance phenotype with lower plant length, higher tiller numbers, reduced and delayed seed germination rate, and decreased pollen viability, seed setting rate and grain yield per plant. Tolerance to multiple abiotic stresses (drought, salinity, and chilling) was also reduced in transgenic plants in association with inhibition of antioxidant enzyme activities under stressed conditions. Our results suggest that Spd and Spm are essential for maintenance of normal plant growth, pollen viability, seed setting rate, grain yield and stress tolerance in rice.