Changes in gene expression during development and thermogenesis in Arum

Thermogenesis in Arum species is induced by salicylic acid (SA) and caused by activation of the alternative respiration pathway and the alternative ox idase (AOX), resulting in heat production. The enzymes phosphoenolpyruvate carboxylase (PEPCase) and NAD-dependent malic enzyme (NAD-ME) also show dra matic increases in activity during thermogenesis and are essential for heat generation. In this current study, we characterized the timing and localiz ation of changes in levels of AOX, NAD-ME, and PEPCase polypeptide accumula tion, and changes in Ppc and Me mRNA accumulation, in various Arum tissues during prethermogenic development and during thermogenesis. In addition, ch anges in ribulose-1,5- bisphosphate carboxylase/oxygenase (Rubisco) gene ex pression were analysed at the level of rbcL protein and mRNA accumulation. AOX, PEPCase, and NAD-ME all increased only in clubs during development, in creasing 5-6-fold by the latest prethermogenic stage and remained at this l evel. The induction of thermogenesis did not cause any changes in levels of AOX, indicating that SA does not affect levels of the enzyme itself, but i nstead must act to stimulate activity. Reported increases in NAD-ME activit y during club development correlated closely with mRNA and protein accumula tion, whereas PEPCase activity appears to be determined by post-transcripti onal and post-translational processes. Interestingly, Rubisco protein and m RNA were found in relatively abundant amounts in clubs during early develop mental stages, and disappeared rapidly as the thermogenic enzymes began to increase in abundance. The induction of thermogenesis by a synthetic induce r of plant pathogen resistance, 2,6-dichloroisonicotinic acid, as well as t he involvement of SA and AOX in both processes, reinforces evidence for a l ink between mechanisms controlling disease resistance in all plants and the rmogenic induction in Arum.