Role of Hsp17.4-CII as coregulator and cytoplasmic retention factor of tomato heat stress transcription factor HsfA2.
HsfA2 is a heat stress (hs)-induced Hsf in peruvian tomato (Lycopersicon peruvianum) and the cultivated form Lycopersicon esculentum. Due to the high activator potential and the continued accumulation during repeated cycles of heat stress and recovery, HsfA2 becomes a dominant Hsf in thermotolerant cells. The formation of heterooligomeric complexes with HsfA1 leads to nuclear retention and enhanced transcriptional activity of HsfA2. This effect seems to represent one part of potential molecular mechanisms involved in its activity control. As shown in this paper, the activity of HsfA2 is also controlled by a network of nucleocytoplasmic small Hsps influencing its solubility, intracellular localization and activator function. By yeast two-hybrid interaction and transient coexpression studies in tobacco (Nicotiana plumbaginifolia) mesophyll protoplasts, we found that tomato (Lycopersicon esculentum) Hsp17.4-CII acts as corepressor of HsfA2. Given appropriate conditions, both proteins together formed large cytosolic aggregates which could be solubilized in presence of class CI sHsps. However, independent of the formation of aggregates or of the nucleocytoplasmic distribution of HsfA2, its transcriptional activity was specifically repressed by interaction of Hsp17.4-CII with the C-terminal activator domain. Although not identical in all aspects, the situation with the highly expressed, heat stress-inducible Arabidopsis HsfA2 was found to be principally similar. In corresponding reporter assays its activity was repressed in presence of AtHsp17.7-CII but not of AtHsp17.6-CII or LpHsp17.4-CII.
Port
Markus
M
Biocenter of the Goethe University, D-60439 Frankfurt am Main, Germany.
Tripp
Joanna
J
Zielinski
Dirk
D
Weber
Christian
C
Heerklotz
Dirk
D
Winkelhaus
Sybille
S
Bublak
Daniela
D
Scharf
Klaus-Dieter
KD
D029681:Arabidopsis Proteins; D001483:Base Sequence; D003593:Cytoplasm / Q000378:metabolism; D017931:DNA Primers; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004591:Electrophoresis, Polyacrylamide Gel; D000076249:Heat Shock Transcription Factors; D006360:Heat-Shock Proteins / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D006358:Hot Temperature; D018551:Solanum lycopersicum / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D010940:Plant Proteins / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D011523:Protoplasts / Q000378:metabolism; D014026:Nicotiana / Q000378:metabolism; D014157:Transcription Factors / Q000378:metabolism*
D029681:Arabidopsis Proteins; D017931:DNA Primers; D004268:DNA-Binding Proteins; C000620134:HSFA2 protein, Arabidopsis; D000076249:Heat Shock Transcription Factors; D006360:Heat-Shock Proteins; D010940:Plant Proteins; D014157:Transcription Factors