Submitted to: Plant and Soil
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/20/2001
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 these studies we report the isolation and characterization of two novel genes from white lupin that are expressed as an adaptation to low P. These genes are P transport genes and are crucial for uptake of P from soil. One of the P transport genes designated LaPT1 is expressed specifically in brushy roots of P-stressed white lupin, while the other P transporter gene occurs in all tissues. The enhanced expression of LaPT1 in brushy roots explains why the P uptake efficiency of these roots is very high. This work is important because: 1) it explains, in part, how white lupin is well adapted to a low P environment; and 2) it may allow us to improve P acquisition even further if we can overexpress LaPT1. Future experiments will be aimed at enhancing P transporter genes in crop species.
Technical Abstract: Two full-length cDNAs encoding putative plant phosphate (Pi) transporters were isolated from proteoid roots of Pi-starved white lupin plants 7 and 10 days after emergence. The deduced amino acid sequences of LaPT1 and LaPT2 are 75.7% identical and both display the typical 12 membrane spanning domains characteristic of other plant Pi transporters. The LaPT1 gene transcript was expressed most strongly in -P roots (both normal and proteoid) and less so in -P stems and leaves. Transcripts of LaPT1 gene were low to nondetectable in +P plants. The LaPT2 gene transcript was highly expressed in roots in both +P and -P treatments. LaPT1 gene is much more dramatically induced by P deficiency over time, and is more highly expressed in -P proteoid than -P normal root tissue. In contrast LaPT2 gene expression was fairly similar over time and in +P and -P normal and -P proteoid roots. While LaPT1 gene was expressed only under P deficiency, LaPT2 gene was uniformly expressed by plants exposed to excess Al and deficiencies of N, Mn, Fe, and P. The LaPT1 gene was isolated and shown to have two exons interrupted by one intron. The sequence of the 5'-upstream putative promoter was determined.