Eucalyptus

photo JM Gion, CIRAD

Its rapid growth as well as its wood quality make eucalyptus the first plant species for industrial plantations in the world. It is also a good model for forest species for genomic approaches on wood formation and adaptation to abiotic stresses according to its small genome size, the availability of genetic maps and QTLs.

The different Eucalyptus projects being carried on in our research institute aim at deciphering the molecular mechanisms involved in wood formation and cold tolerance. Furthermore, beyond these studies of fundamental importance, both teams involved in these projects are determined in finding industrial developments in relationship with wood quality improvement and the broadening of the geographical areas of industrial plantations towards temperate zones, including France.

Genetic control of wood formation

Our research work focuses on a plant specific developmental process which gives rise to the formation of a highly specialised complex tissue, the secondary xylem. In trees, wood or secondary xylem, originates from a meristematic tissue, the vascular cambium. The formation of xylem is a fascinating example of differentiation which necessitates the spatial and temporal coordination of the expression of several hundreds of genes involved in cell division, elongation, formation of a lignified secondary wall and programmed cell death. The secondary walls of xylem cells possess unique characteristics (biochemical composition and tridimensional association of polymers) which govern the intrinsic properties of wood of forestry trees.

The aim of our project is to identify and functionally characterize the genes involved in the genetic control of wood quality in Eucalyptus, more particularly transcription factor genes involved in xylogenesis. The developped strategy consists in searching a statistical relationship between a polymorphism of candidate genes and permanent quantitative features related to wood quality. This issue is carried on in a collaborative project with CIRAD through genetic mapping of the candidate genes and search for colocalisation with QTLs related to wood quality.

In order to identify putative candidate genes related to wood formation, 13,000 ESTs from one normalized Eucalyptus xylem cDNA library and several SSH subtractive libraries containing xylem-preferentially expressed genes will be sequenced in the frame of this project.

Genes involved in cold tolerance

This program on Eucalyptus is focused on the molecular mechanisms associated with cold, a very important environmental factor affecting plant growth, productivity and plantation areas, especially in France. Based on a transcriptome analysis, the project aims to identify and study a pool of genes involved in the intrinsic cold tolerance as well as in the induced tolerance, known as cold acclimation and occurring after a cold treatment (non-freezing temperature) associated with a decrease of light and photoperiod.

First goal of our program concerns the in-depth functional study of selected genes to understand the mechanisms of frost tolerance, and the second goal is the identification of candidate genes for the design of reliable markers for assisting genetic selection (MAS).

In a first step, two cDNA libraries were made as sources of genes: a subtractive acclimation cDNA library from a cell suspension culture and a total cDNA library from leaves of cold acclimated plantlets (cold-tolerant genotype). 13,000 clones from these libraries will be sequenced in this project.