|Liu, Hong - PLANT BIOLOGY UOFI URBANA|
Submitted to: Plant Physiology Supplement
Publication Type: Abstract Only
Publication Acceptance Date: September 1, 1997
Publication Date: N/A
Technical Abstract: While the low temperature sensitivity of photosynthesis in chilling-sensitive plants, such as tomato is well known, how these plants sense the chilling signal that eventually causes the malfunction of photosynthesis remains unknown. Previous data shows that chilling may affect the phosphorylation and dephosphorylation of certain proteins and eventually affect the expression of photosynthetic-related genes. In this study, we further analyzed the phosphoprotein profile on SDS-PAGE and found that there is a protein (-37kD) that is highly phosphorylated during the initial moments of rewarming following an overnight chilling treatment. This protein pp**37 was phosphorylated on serine/threonine residues judged by the effects of kinase inhibitors, sensitivity to alkali treatment, and that the phosphorylation can be prevented by a PKC inhibitor. Experiments with Ca**2+ related inhibitors revealed that pp**37 was phosphorylated via a Ca**2+-dependent and, probably, calmodulin-independent protein kinase. Okadaic acid, a protein phosphatase inhibitor, can also effectively prevent the phosphorylation of pp**37 suggesting that there may be an upstream kinase or regulator activated in dephosphorylated state after chilling treatment. By in vitro PKC assay and in gel kinase assay with histone, it was shown that there are two kinases activated sequentially during the initial of rewarming. The phosphoprotein pp**37 was isolated and further purified by HPLC but microsequencing of the initial 10 amino acids of N terminal sequence showed no high homology with any known genes. We are now trying to clone the gene encoding pp**37 by using asymmetric PCR based on a regenerated specific primer and oligo(dT).