Submitted to: Plant Physiology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 8/16/2005
Publication Date: 11/1/2005
Citation: Park, S., Cheng, N., Pittman, J.K., Yoo, K.S., Park, J., Smith, R.H., Hirschi, K. 2005. Increased calcium levels and prolonged shelf life in tomatoes expressing Arabidopsis h+/ca2+ transporters. Plant Physiology. 139:1194-1206. Interpretive Summary: An important goal for agbiotechnology is to increase the shelf life and disease resistance of plants. Here we have manipulated tomatoes to express higher levels of a calcium transporter. The plants contain higher levels of calcium and have increased shelf-life. Furthermore, they may be more tolerant of some pathogens. This is a major advancement in our ability to alter agriculturally important crops.
Technical Abstract: Here we demonstrate that fruit from tomato (Lycopersicon esculentum) plants expressing Arabidopsis (Arabidopsis thaliana) H(+)/cation exchangers (CAX) have more calcium (Ca(2+)) and prolonged shelf life when compared to controls. Previously, using the prototypical CAX1, it has been demonstrated that, in yeast (Saccharomyces cerevisiae) cells, CAX transporters are activated when the N-terminal autoinhibitory region is deleted, to give an N-terminally truncated CAX (sCAX), or altered through specific manipulations. To continue to understand the diversity of CAX function, we used yeast assays to characterize the putative transport properties of CAX4 and N-terminal variants of CAX4. CAX4 variants can suppress the Ca(2+) hypersensitive yeast phenotypes and also appear to be more specific Ca(2+) transporters than sCAX1. We then compared the phenotypes of sCAX1- and CAX4-expressing tomato lines. The sCAX1-expressing tomato lines demonstrate increased vacuolar H(+)/Ca(2+) transport, when measured in root tissue, elevated fruit Ca(2+) level, and prolonged shelf life but have severe alterations in plant development and morphology, including increased incidence of blossom-end rot. The CAX4-expressing plants demonstrate more modest increases in Ca(2+) levels and shelf life but no deleterious effects on plant growth. These findings suggest that CAX expression may fortify plants with Ca(2+) and may serve as an alternative to the application of CaCl(2) used to extend the shelf life of numerous agriculturally important commodities. However, judicious regulation of CAX transport is required to assure optimal plant growth.