Analysis of gene expression in Kalanchoe daigremontiana leaves during plantlet formation under drought stress
Background: Kalanchoe daigremontiana is an attractive model system for the study of the molecular mechanisms of somatic embryogenesis and organogenesis competence due to its formation of plantlets with adventitious roots on the leaf margins that are derived from somatic embryos. The suppression subtractive hybridization technique was used to investigate gene expression during asexual reproduction. Leaves from plants subjected to drought stress provided the source of ‘Tester’ DNA, and leaves from plants grown under normal conditions provided the ‘Driver’ DNA for subtractive hybridization. Results: A total of 481 high quality ESTs were generated, which clustered into 390 unigenes. Of these unigenes, 132 grouped into 12 functional categories, suggesting that asexual reproduction is a complicated process involving a large number of genes. The expression characteristics of selected genes from the SSH library were determined by real-time PCR and were classified into five groups, suggesting that gene expression patterns during asexual reproduction are complex. Up-regulation of S-adenosylhomocysteine hydrolase suggested that a decrease in cytokinin levels promotes the initiation of plantlet formation. Many other genes, such as inorganic pyrophosphatase and glutamate decarboxylase, play important roles in gene regulation during asexual reproduction. Conclusion: Our results provide a framework and unified platform on which future research on asexual reproduction in K. daigremontiana can be based. This represents the first genome-wide study of asexual reproduction in K. daigremontiana.