Submitted to: Plant Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/10/2001
Publication Date: N/A
Interpretive Summary: Phosphorus (P) is a major nutrient required for plant growth. However, crop growth is limited on 40% of the world's soils due to lack of available P. Moreover, world reserves of P are projected to become limiting in 60-80 years. To develop plants that are more efficient and require less P, we need to understand how they adapt to and acquire P in an environment lacking sufficient sources of P. The legume crop white lupin is capable of growing in very low P soils. We have been evaluating the biochemical and molecular adaptations that white lupin displays under low P. Two very novel responses that white lupin shows in response to low P are the development of unusual roots that are very brushy and the secretion of enzymes (protein catalysts) from these brushy roots. In this report we identify a novel enzyme that is secreted from white lupin brushy roots due to the stress of low P. This enzyme, called acid phosphatase, can break down soil organic matter that contains P and release it for plant growth. We describe the acid phosphatase protein and show how it is secreted from brushy roots. We also isolate the gene encoding the white lupin acid phosphatase and measure how much the gene is expressed in various plant organs. Moreover, we show that similar genes occur in other plant species. This research is useful because it provides us with a tool, acid phosphatase, that may be useful in improving P nutrition in all plants. In future studies we plan to increase the synthesis of acid phosphatase in white lupin and other crops to improve P acquisition.
Technical Abstract: White lupin grown under phosphorus (P) deficiency displays a suite of highly coordinated adaptive responses. Included among these is secretion of copious amounts of acid phosphatase (APase). Although numerous reports document that plants secrete APases in response to P deficiency, little is known of the biochemical and molecular events involved in this process. Here we characterize the secreted APase protein, cDNA, and gene from white lupin. The secreted APase enzyme is a glycoprotein with broad substrate specificity. It is synthesized as a preprotein with a deduced Mr of 52 kD containing a 31 amino acid presequence. Analysis of the presequence predicts that the protein is targeted to outside the cell. The processed protein has a predicted Mr of 49 kD but migrates as a 70 kD protein on SDS gels. This is likely due to glycosylation. Enhanced expression is fairly specific to proteoid roots of P-stressed plants and involves enhanced synthesis of both enzyme protein and mRNA. Secreted APase appears to be encoded by a single gene containing seven exons interrupted by six introns. The 5'-upstream putative promoter of the white lupin secreted APase contains a 50 bp region having 72% identity to an Arabidopsis APase promoter that is responsive to P deficiency. The white lupin secreted APase promoter and targeting sequence may be useful tools for genetically engineering important proteins from plant roots.