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Effects of Gravity on Gene Expression in the Maize Pulvinus: Unraveling the Roles of Transcription and Translation.  H. Myburg¹, R. Salinas-Mondragon¹, R.L. Hammond¹, I.Y. Perera¹, E. Davis¹, C.S. Brown^1,2 and H. Winter Sederoff¹.  Plant Sensory Genomics Group, ¹Dept. of Plant Biology, ²Kenan Institute for Science, Technology & Engineering, North Carolina State University, Raleigh, NC, 27695. 

   Gravitropic bending in cereal grass stems is brought about by differential growth of the pulvinus, a specialized tissue that senses and responds only to gravity.  Previous work has shown that translational regulation of specific transcripts is correlated with the extent of asymmetric cell elongation in the maize pulvinus and may be a central controlling step in the initiation of a growth response during gravitropism (Heilmann et al. 2001).  Global changes in the steady-state levels of transcripts (transcriptional control) and transcript recruitment into polyribosomes (translational control) were assessed by DNA microarray analysis.  We compared transcript abundance changes in response to 90º reorientation during the first hour between upper (slow elongation) and lower (fast elongation) halves of the most gravity competent pulvini.  For each sample we purified and fractionated total mRNA and polyribosome-associated mRNA and analyzed transcript profiles using Affymetrix GeneChip® Maize Genome Arrays.  A total of 13584 transcripts were screened in a time course ranging from 2 minutes up to one hour.  More than 540 transcripts showed a response to gravity.  Within this group the majority of the transcripts seem to be transcriptionally regulated while a smaller group of transcripts show regulation at the translational level.  We will discuss the implications of translational regulation on gravitropic responses and compare possible functional roles for translationally regulated genes.

Heilmann, I., J. Shin, J. Huang, I.Y. Perera and E. Davies (2001) Transient Dissociation of Polyribosomes and Concurrent Recruitment of Calreticulin and Calmodulin Transcripts in Gravistimulated Maize Pulvini.  Plant Physiol. 127(3): 1193-1203.

(Supported by NASA grant NNA04CC56G to HWS and NSCU RNA biology fellowship to RLH.)