Ectopic expression of the PttKN1 gene induced altered leaf morphology and hormonal levels in transgenic tobacco

Abstract

PttKN1 (Populus tremula × tremuloides KNOTTED1) gene plays an important role in plant morphological formation. To investigate the gene functions, it was introduced into tobacco using the leaf disc method. The transgenic tobacco lines displayed various morphologies different from those of wild type. The results of RT-PCR suggested that these morphological alterations were caused by the ectopic expression of the PttKN1 gene. Notably, almost all the transgenic lines displayed phenotypes sporadically except for one, which appeared with wrinkled leaves throughout the plant growth. The plant grow two round stems compared to one of the wild type, and have mild, intermediate or severe wrinkled leaves distributed on both of the stems. The results of RT-PCR, hiTAIL-PCR and Southern blot analysis indicated that the foreign PttKN1 gene was integrated into the genome of the plant by the way of direct repeats with two copies. Further study on endogenous hormonal levels from HPLC showed that the CK (cytokinin) level was increased and GA (gibberellins) level was decreased in the transgenic line. Correspondingly, the expression of GA 20-oxidase gene that related to GA biosynthesis was down-regulated. These data demonstrated that the ectopic expression of the PttKN1 gene induced aberrant leaf morphology and endogenous hormonal levels in transgenic tobacco, which would enhance our understanding on the functions of PttKN1 gene in leaf development.