Transcriptional and post-transcriptionnal regulations in response to stress: a case study in rubber tree

In response to abiotic and anthropogenic constraints that are associated with latex harvesting, a change in the distribution of small RNAs has been observed in latex cells concurrently with physiological disorders that stop latex flow (Tapping Panel Dryness, TPD). Small RNAs are negative ribo-regulators of gene expression that act either at the transcriptional level (class size 23- 25 nt) or at the post-transcriptional one (class size 20-22 nt). We observed a major peak of 24 nt of small RNA in the latex of healthy trees and 21 nt in TPD-affected trees. Using the sequenced genome from rubber tree clone PB 260, we annotated MIR genes and miRNAs, as well as transposable elements (TEs). Our results showed that the small 21-nt RNAs accumulating in the latex of TPDaffected trees were not MIR genes-derived miRNAs and might therefore belong to the subclass of epigenetically-activated siRNAs (easiRNA). TEs annotation shows that they make up two third of clone PB 260's genome size. In order to evaluate the contribution of small RNAs-dependent posttranscriptional gene silencing to TPD, we performed the high-throughput sequencing of 3' ends mRNA degradation products (or 'degradome' sequecing) in 6 tissues. In the light of our results, we discuss how these new insights into TPD contribute to a better understanding of the complex influence of stresses on regulatory networks modulating gene expression