Enhancement of abiotic stress tolerance in poplar by overexpression of key Arabidopsis stress response genes, <Emphasis Type="Italic">AtSRK2C</Emphasis> and <Emphasis Type="Italic">AtGolS2</Emphasis>

Recent environmental issues have increased the demand for woody biomass as a renewable resource for industry and energy. For a stable supply of woody biomass, it is critical to decrease the effects of abiotic stresses, such as drought and salinity, which hinder plant growth. For the goal to develop practical stress-tolerant trees, we generated transgenic poplar plants (P. tremula × tremuloides), in which a key Arabidopsis regulatory factor involved in stress responses, SNF1-related protein kinase 2C (AtSRK2C), or galactinol synthase 2 (AtGolS2), was overexpressed. Both types of transgenic poplar plants displayed higher tolerance to abiotic stresses, in comparison with nontransgenic plants, indicating that AtSRK2C and AtGolS2 can function in the abiotic stress response pathway of poplar. We also examined the expression profiles of ten poplar genes putatively homologous to well-known Arabidopsis stress response genes and found that several of the poplar genes showed different responses to abiotic stress from their Arabidopsis counterparts. Whereas the overexpression of AtSRK2C in transgenic Arabidopsis plants was reported to upregulate the expression of endogenous genes, the overexpression of AtSRK2C or AtGolS2 in transgenic poplar did not. Taken together, our findings suggest that the details of the underlying molecular mechanisms of the abiotic stress response may differ, but that the key regulatory factors in Arabidopsis and poplar have common features and are effective molecular targets for further breeding to enhance abiotic stress tolerance in poplar.     

Chitinase Gene Expression in Response to Environmental Stresses in Arabidopsis thaliana: Chitinase Inhibitor Allosamidin Enhances Stress Tolerance

The expression levels of three chitinase genes in Arabidopsis thaliana, AtChiA (class III), AtChiB (class I), and AtChiV (class IV), were examined under various stress conditions by semi-quantitative RT-PCR. Under normal growth conditions, the AtChiB and AtChiV genes were expressed in most organs of Arabidopsis plants at all growth stages, whereas the AtChiA gene was not expressed at all. The class III AtChiA gene was expressed exclusively when the plants were exposed to environmental stresses, especially to salt and wound stresses. Treatment of Arabidopsis plants with allosamidin, which inhibits class III chitinases, did not affect the growth rate. Surprisingly, however, the plants treated with allosamidin were more tolerant of abiotic stresses (cold, freezing, heat, and strong light) than the control plants. It also appeared that allosamidin enhances AtChiA and AtChiB expression under heat and strong light stresses. Allosamidin is likely to enhance abiotic stress tolerance, probably through crosstalk between the two signaling pathways for biotic and abiotic stress responses.