Expression of KxhKN4 and KxhKN5 genes in Kalanchoë blossfeldiana 'Molly' results in novel compact plant phenotypes: towards a cisgenesis alternative to growth retardants.

Many potted plants like Kalanchoë have an elongated natural growth habit, which has to be controlled through the application of growth regulators. These chemicals will be banned in the near future in all the EU countries. Besides their structural functions, the importance of homeotic genes to modify plant architecture appears evident. In this work, the full length cDNA of five KNOX (KN) genes were sequenced from K. x houghtonii, a viviparous hybrid. Two constructs with the coding sequence of the class I and class II homeobox KN genes, KxhKN5 and KxhKN4, respectively, were overexpressed in the commercially important ornamental Kalanchoë blossfeldiana 'Molly'. Furthermore, a post-transcriptional gene silencing construct was made with a partial sequence of KxhKN5 and also transformed into 'Molly'. Several transgenic plants exhibited compact phenotypes and some lines had a relative higher number of inflorescences. A positive correlation between gene expression levels and the degree of compactness was found. However, a correlation between the induced phenotypes and the number of inserted copies of the transgene were not observed, although line '70-10' with a high copy number also had the highest expression level. Moreover, overexpression of KxhKN4 resulted in plants with dark green leaves due to an elevated content of chlorophyll, a highly desired property in the ornamental plant industry. These transgenic plants show that a cisgenesis approach towards production of compact plants with improved quality as an alternative to chemical growth retardants may be feasible.