Poster: Organelle biogenesis

Abs # 630: Analysis of developing maize plastids reveals two mRNA stability classes correlating with RNA polymerase type

Presenter:	Cahoon, A. Bruce , acahoon@mtsu.edu
Authors	Cahoon, A. Bruce  (A)   Harris, Faith M (B)   Stern, David S (B)
Affiliations:	(A): Middle Tennessee State University (B): Boyce Thompson Institute for Plant Research

The plastid genome is transcribed by two distinct RNA polymerases, the PEP encoded by the plastid genome, and the NEP encoded in the nucleus. An early model of plastid transcription suggested that the NEP is responsible for the transcription of housekeeping genes needed early in development, and that the PEP transcribes genes required for photosynthesis. Recently this model was challenged by the discovery that all plastid genes are transcribed by NEP in PEP deficient tobacco plastids, suggesting that mRNA turnover may play a strong role in previously observed transcription patterns. In this study we have used the developmental gradient of plastids found along maize leaves to further test this model. We provide evidence that the NEP enzyme steady state levels decrease as plastids mature. In contrast, production of mRNA’s by NEP increases as plastids mature yet their steady state levels remain constant. These results suggest that as plastids mature NEP may become more active and that mRNAs produced by the enzyme become more stable. We propose a modified model based on these results.