Phosphate exists in the soil solution as one of three orthophosphate species (H 3PO 4, H 2PO 4 –, and HPO 4 2 –) depending on the pH ( Bohn et al., 1979). Plants acquire P in the form of phosphate from the soil solution via their roots. Phosphorus (P), an essential mineral nutrient for plants, is required in large amounts to maintain growth ( Raghothama, 1999 Abel et al., 2002). Transferring this technology to crops would allow precision management of P fertilization, thereby maintaining yields while reducing costs, conserving natural resources, and preventing pollution. Hence, smart plants can monitor plant P status. Leaves of Arabidopsis bearing a SQD1:: GUS construct showed increased GUS activity after P withdrawal, which was detectable before P starvation limited growth. ![]() The expression of SQD1, a gene involved in the synthesis of sulfolipids, responded specifically to P starvation and was increased 100 h after withdrawing P. Shoots had reduced P after 100 h, but growth was unaffected. A literature survey indicated that the expression of many of these “late” genes responded specifically to P starvation. This lull in differential gene expression preceded the differential expression of a new group of 61 genes 100 h after withdrawing P. Surprisingly, the expression of only four genes differed between shoots of P-starved and -replete plants 28 h after P was withdrawn. However, two common putative cis-regulatory elements (a PHO-like element and a TATA box-like element) were present significantly more often in the promoters of genes whose expression increased 4 h after the withdrawal of P compared with their general occurrence in the promoters of all genes represented on the microarray. The transient changes in gene expression occurring immediately (4 h) after P withdrawal were highly variable, and many nonspecific, shock-induced genes were up-regulated during this period. First, using microarrays, we identified genes whose expression changed more than 2.5-fold in shoots of plants growing hydroponically when P, but not N or K, was withheld from the nutrient solution. Smart plants can be genetically engineered by transformation with a construct containing the promoter of a gene up-regulated specifically by P starvation in an accessible tissue upstream of a marker gene such as β-glucuronidase ( GUS). ![]() Our aim was to generate and prove the concept of “smart” plants to monitor plant phosphorus (P) status in Arabidopsis.
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