Forest Tree Transgenesis and Functional Genomics: From Fast Forward to Reverse Genetics

摘要

Genomics has become an integral part of the forest tree improvement, and gene structural and expressional data are being produced at an unprecedented rate. However, biological resources in the form of tagged mutants are still lacking in forest trees,which at present is a missing part of tree genomics. The potential bottlenecks here are the steps involving plant transformation, which is instrumental both in reverse and forward genetics strategies aimed at to determine gene function. With few exceptions, genetic transformation is an obligatory final step by which traits are engineered into plants. For basic research transgenesis is the method of choice to confirm gene function, after deductions made through comparative genomics, expression profiles,and mutation analysis. The biological features of long-lived tree species create obstacles as well as provide opportunities to design new approaches to overcome the barriers associated with forest tree genomics. To understand how a cell works we need toknow the function of almost every gene in its genome. Genome sequencing provides a tremendous amount of information for the development of global approaches towards this goal, complementing and enhancing the more traditional (single-gene) approaches. Genome sequencing has been completed in model plant Ara-bidopsis (The Arabidopsis Genome Initiative, 2000) and in rice (GoFF et al, 2002; Yu et al., 2002), a model cereal. Similarly, forest biologists have given enough justification to sequence Populus genome as a model for trees and woody perennials (WuLLSCHLEGER et al., 2002; TAYLOR, 2002), A 6X coverage of the black cottonwood (Populus trichocarpa) genome as first tree genome will be available in public domain by the end of the year 2003 (InternationalPopulus Genome Consortium) Once whole-genome information is available for an organism, the challenge turns from identifying the parts to understanding their function as well as to improving genome structure, thus ushering in the 'post-genomic' era. In the short term, the first goal is to assign some element of function to each of the genes in an organism also referred to as 'functional genomics', and to do this with high-throughput, systematic approaches-Major challenges of functional genomics in treesare to assess tree growth and wood yield. These parameters are important in terms of wood quality like strength and fibre length, and renewable energy resources (CHAFFEY et al., 2002; CAMPBELL et al., 2003; CONFALONIERI et al., 2003). With most of the Populus genome still to be assigned function, the notion of accumulating this information one gene at a time is hard to contemplate. This knowledge gap has been the crucial impetus for developing 'whole-genome' approaches that can acquire functional information, in the form of expression profiles, protein-protein interactions, computational approaches and the response to loss or gain of function by mutation.