Differential regulation of Lehsp23.8 in tomato plants: Analysis of a multiple stress-inducible promoter.

Small heat shock proteins (sHSPs) are the major family of HSP induced by heat stress in plants. In this report, an approximately 1.9kb of Lehsp23.8 5'-flanking sequence was isolated from tomato genome. By using the β-glucuronidase (GUS) reporter gene system, the developmental and tissue specific expression of the gus gene controlled by the Lehsp23.8 promoter was characterized in transgenic tomato plants. Strong GUS staining was detected in the roots, leaves, flowers, fruits and germinated seeds after heat shock. The heat-induced GUS activity was different in the floral tissues at various developmental stages. Fluorometric GUS assay showed that the heat-induced GUS activity was higher in the pericarp than in the placenta, and it was the lowest in the locular gel. The heat-shock induction of the Lehsp23.8 promoter depended on the different stages of fruit development. The optimal heat-shock temperatures leading to the maximal GUS activity in the pericarp of green, breaker, pink and red fruits were 42, 36, 39 and 39°C, respectively. The heat-induced GUS activity in tomato fruits increased gradually within 48h of treatment and weakened during tomato fruit ripening. Obvious GUS activities under cold, exogenous ABA and heavy metal (Cd(2+), Cu(2+), Pb(2+) or Zn(2+)) stress conditions were also detected. These results show that the Lehsp23.8 promoter is characterized as strongly heat-inducible and multiple-stress responsive.