biologia plantarum

Biologia plantarum 52:695-702, 2008 | DOI: 10.1007/s10535-008-0134-0

The ubiquitin/proteasome pathway from Lemna minor subjected to heat shock

A. S. Caeiro¹, P. C. Ramos², A. R. Teixeira³, R. B. Ferreira^1,3,*

¹ Instituto de Tecnologia Química e Biológica, Universidade Nova de Lisboa, Oeiras, Portugal

² Departamento de Química e Bioquímica, Faculdade de Ciências e Tecnologia, Universidade do Algarve, Faro, Portugal

³ Departamento de Botânica e Engenharia Biológica, Instituto Superior de Agronomia, Universidade Técnica de Lisboa, Lisboa, Portugal

Exposure of Lemna minor L. to high temperatures leads to an initial decrease in the ubiquitin (Ub) monomer pool size and the accumulation of high molecular mass Ub-protein conjugates, possibly reflecting an increment in the supply of protein substrates to the Ub/proteasome pathway. Alternative explanations include, for example, changes in the transcription rates of one or more pathway components. To measure the effect of heat shock on the simultaneous rates of transcription of selected genes encoding five Ub pathway components (Ub, E1, E2, β subunit and ATPase subunit of the 26S proteasome), a semi-quantitative RT-PCR method was developed using cDNA normalized against the housekeeping gene encoding the 18S ribosomal RNA. Whilst Ub transcription is abruptly increased, there is a moderate increment in the transcription of E1 and the β subunit, a moderate reduction in the transcription of the ATPase subunit and a marked reduction in the case of E2, indicating a differential transcription pattern of the various components of the Ub/proteasome pathway in L. minor subjected to high temperatures. These observations suggest that the increment in the Ub/proteasome pathway intermediates is due to an augmented supply of substrates derived from the stress-induced damage imposed on the cellular proteins. The initial build up of intermediates occurs not only at the expense of the pre-existing pool of free Ub, but also as a result of the prompt increase in Ub expression.

Keywords: ATPase subunit; duckweed; semi-quantitative RT-PCR; transcription

Subjects: ATPase; growth analysis, biomass and yield enhancement; heat stress, high temperature; Lemna minor; polymerase chain reaction (PCR); proteins; RNA; temperature, high; temperature, high

Received: September 26, 2006; Accepted: July 25, 2007; Published: December 1, 2008  Show citation