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Project
III. Changes in plant gene expression during and after gravistimulation
(Davies,
Sederoff,
and Whetten).
This research effort is one of five integrated projects that in their
totality comprise the NSCORT in Gravitational Biology. As such, Project
III is focused on identifying those genes whose expression is altered
during and after gravity-stimulation of pine (compression wood) and maize
plants (pulvinus). We are identifying genes whose expression changes (either
up-regulated or down-regulated) and which might be involved in the sensing
stage, the signal transduction phase and/or the growth response. We are
also looking at changes occurring in the very early stages of
sensing/transduction at the level of transcription as well as translation
and in genes that are expressed unequally on the upper and lower sides
of gravistimulated plants.
In the maize pulvinus, we have identified two transcripts encoding calcium-responsive proteins whose level increases in both sides, but whose recruitment into polysomes is greater and faster (within 15 minutes) on the lower side (Heilmann et al. 2001). This is the most rapid translational response reported after gravi-stimulation in the maize pulvinus system to date and may be one of the fastest in any plant system challenged by an altered gravity stimulus. We have also shown thatthe asymmetric increases in polysomes (more on lower than upper side) occur not only in the growth-responsive pulvinus, but also in the non-responsive pulvinus. Apparently the non-responsive pulvinus can sense gravity even though it does not exhibit a growth response. We are now looking to see if the same transcripts are made and recruited into polysomes in both kinds of pulvini.
With pine, we have looked primarily at transcriptional changes and are using microarray analysis to identify the totality and complexity of global changes (Sun 2001; Whetten et al. 2001). We have also focused on the genes involved in the growth response, especially those related to lignin biosynthesis, since pine is the model system for such studies and compression wood is a major practical problem in the pulp and paper industry. The use of microarray technology is now being expanded to include maize and Arabidopsis.