Transcriptional Regulation and Function of hsr203J, an Hypersensitivity-Related Gene of Tobacco Activated in Response to Ralstonia solanacearum

International audienc

Further progress towards a catalogue of all Arabidopsis genes: analysis of a set of 5000 non-redundant ESTs

International audienc

Spatial-resolved analysis of histological and biochemical alterations induced by water-soaking in melon fruit.

Water-soaking, a physiological disorder characterised by a glassy texture of the flesh, depreciates greatly the commercial quality of early-season Charentais cantaloupe melons (Cucumis melo L. cv. Talma). Although it is accepted that the genotype and a number of physiological and environmental factors play a role in the development of the syndrome, the intimate mechanisms responsible for water-soaking remain unknown. We report here on an integrated study of the development of water-soaking in fruit. Using nuclear magnetic resonance (NMR) imaging, we have shown that water mobility increased in the diseased tissues. Alteration of the cell wall and the presence of large intercellular spaces were correlated with a severe depletion of cell wall calcium. Water-soaking developed during the late stages of fruit ripening, but no correlation was found with ethylene biosynthesis. Thus, fruits in which ethylene action was blocked by 1-methylcyclopropene remained sensitive to water-soaking. Moreover, the expression of two genes encoding key enzymes in ethylene biosynthesis remained unchanged in response to water-soaking. The major changes observed concerned a protein implicated in calcium signalling processes. While the amount of total calmodulin, the ubiquitous calcium binding protein, was not modified, a particular calmodulin-binding protein (CaM-BP) was absent in water-soaked but not in sound mature tissues. This CaM-BP may be a marker or a determinant of this physiological disorder

AtCML8, a calmodulin-like protein, differentially activating CaM-dependent enzymes in Arabidopsis thaliana

Plants express many calmodulins (CaMs) and calmodulin-like (CML) proteins that sense and transduce different Ca(2+) signals. Previously, we reported divergent soybean (Glycine max) CaM isoforms (GmCaM4/5) with differential abilities to activate CaM-dependent enzymes. To elucidate biological functions of divergent CaM proteins, we isolated a cDNA encoding a CML protein, AtCML8, from Arabidopsis. AtCML8 shows highest identity with GmCaM4 at the protein sequence level. Expression of AtCML8 was high in roots, leaves, and flowers but low in stems. In addition, the expression of AtCML8 was induced by exposure to salicylic acid or NaCl. AtCML8 showed typical characteristics of CaM such as Ca(2+)-dependent electrophoretic mobility shift and Ca(2+) binding ability. In immunoblot analyses, AtCML8 was recognized only by antiserum against GmCaM4 but not by GmCaM1 antibodies. Interestingly, AtCML8 was able to activate phosphodiesterase (PDE) but did not activate NAD kinase. These results suggest that AtCML8 acts as a CML protein in Arabidopsis with characteristics similar to soybean divergent GmCaM4 at the biochemical levels.close7