Growth and Development of higher plants

Hormonal interactions will also be analyzed at the level of downstream effectors. From recent transcriptome analyses we know that the expression of about 5% of the genes is significantly affected upon response to ethylene. A number of these genes encode proteins potentially involved in cell wall modification. We will focus on well-characterized proteins that play a defined role in the process of cell expansion (H+ ATPases, peroxidases, HRGPs, expansins, aquaporins, XTH’s, glucanases and or cellulose synthases; a selection thereof will be made) (P5, P4 and P1D). The role of specific gene products will first be investigated by analysis of overexpression and/or knock-out lines. For those targets for which the results justify further analysis, misexpression will be done under cell type specific promoters and the behaviour of these lines will be analyzed under normal conditions of growth, as well as under influence of hormone treatments (collaboration P1D - EU1). The latter could be indicative for a yet unidentified point of hormonal interaction. Under WP1, the effects of selected compounds from the chemical library will be investigated on the above-mentioned mutants, and compared to the wild type (P1D in collaboration with P1A).

Within the previous IAP network, P1D was focusing on the ethylene/GA cross-talk. The analysis of double mutants defective in GA and ethylene synthesis or signal transduction, initiated during the previous IAP collaboration, will be finalized. The eto2gai combination will be investigated with specific attention to root development. Differences in root length, number of lateral roots, and root growth rates will be recorded (P1D in collaboration with P1C). The effect of the double deficiency on alterations in the root/shoot ratio will be considered as well.

In summary, a more profound understanding of the interaction of hormone signalling processes both at the level of signalling components and that of effector proteins can be expected. The analysis of cell type specificity of these proteins will add an additional level of insight in the puzzle of signalling cross-talk.