Combining an original method for preserving RNA expression in situ with an effetive RNA method makes it possible to study gene expression in any banana fruit tissue.

Introduction. RNA isolation is a prerequisite to studying gene expression in
banana and to understanding changes occurring in response to the environment. Standard
extraction methods do not efficiently extract RNA from plants such as banana, with high levels
of phenolics, carbohydrates, or other compounds that bind to and/or coprecipitate with RNA.
Materials and methods. Five to seven RNA extraction methods were compared. Four crowntissue
storage methods were also compared. cDNA-AFLP was used to ensure that the obtained RNA
was of sufficient quality for molecular applications and that RNA expression was unaltered by in
situ storage. Results and discussion. The modified hot-borate method proved to be the best
RNA extraction method, allowing high yields of good quality, undegraded RNA from the crown,
fruit peel and pulp at all stages of ripening. The RNA obtained by this method was of sufficient
quality for molecular applications such as cDNA-AFLP that give highly reproducible results.
Freeze-drying of fresh tissues and tissue conservation in hot-borate buffer, two original storage
methods, appear appropriate for preserving RNA in situ without ultra-low temperature. The RNA
obtained was of high quality, undegraded, and useful for all downstream applications. The
genome expression profile obtained by cDNA-AFLP analysis was unaltered by these methods
for storing collected tissues. Conclusion. By applying all the suggested procedures in this work,
it is possible to store and study gene expression in any banana fruit tissue, whatever the maturity
stage, without affecting the RNA expression level.