Erwin Schrödinger Fellowship J 1907 Regulation of cyclin expression & effects on root growth Thomas
POTUSCHAK 06.03.2000
Ectopic expression of the Arabidopsis cyclin B1;1 accelerates root growth without altering the pattern of lateral
root formation (Doerner et all, 1996). Thus cyclin expression is a limiting factor for root apical growth and cyclin
expression might be a target for growth control pathways in plants. Functional analysis with promoter deletion
variants placed upstream of either the same mitotic cyclin or an reporter gene in both transgenic cell cultures as
well as transformed plants has revealed the presence of both quantitative and qualitative promoter elements. The
qualitative promoter elements are responsible for stimulating cyclin expression at the proper time in the cell cycle,
around the G2/M transition, as well as they are sufficient to direct expression to the meristems.
However, the magnitude of cyclin steady state RNA accumulation is approximately tenfold less than that observed
with the full-length promoter. Further analysis has revealed the presence of positive and negative regulatory
elements, which serve to modulate the amplitude of cyclin transcription. The cognate DNA binding comlexes
appear to be the best candidates for effectors of growth control pathways. I want to characterise the previously
identified promoter elements in greater detail and identify the growth control pathways that act on them to affect
root apicat meristem activity via regulation of cyclin transcription. In order to dissect these pathways it is of special
interest to me to clone factors that bind to regulatory factors within the cyclin promoter.
Cloning of these factors will allow the identification of the pathways that act through them and will enable us to
study directly how they effect the regulation of cyclin transcription.