Characterization of phosphate starvation-induced protein phosphatase and a glycerol-3-phosphate permease in Arabidopsis and tomato.

摘要

Phosphate (Pi) is one of the most important but least available plant nutrients found in the soil, this has led to multiple adaptations by plants. These adaptations help plants to enhance Pi availability, uptake and use efficiency. In this study the molecular and biochemical characterization of two gene families that are likely to be involved in the adaptation of plants to phosphate deficiency is presented. They were identified by the technique of RNA subtraction hybridization cloning. Expression of these genes is strongly, and specifically influenced by changes in Pi availability.; The first group represents a novel family of Pi starvation induced phosphatase, referred to as PS2 family. Three members in the Arabidopsis genome represent the PS2 family, and homologs are found in other plants including tomato. The deduced protein appears to be most similar to the phospho-serine phosphatases and possess conserved regions found in the members of halo-acid dehalogenase (HAD) and DDDD (4 aspartate) super families of phosphohydrolases. Western blot analysis showed that the expression of LePS2 message is linked with the accumulation of protein. Further studies with cell cultures were utilized to determine that the LePS2 protein is not excreted, instead it appears to accumulate in the pellet of insoluble cellular debris rather than in the media or the soluble protein fractions. Further studies showed that the transgenic overexpressing plant lines showed a mild phenotype of delayed leaf senescence and delayed flowering. Additionally, the bacterial expressed protein was tested for phosphatase activity. The protein exhibited phosphatase activity against a synthetic phospho-serine/threonine peptide. This data suggests that PS2 family members are likely to function as protein phosphatases.; The second group represents a putative glycerol 3-phosphate permease gene family (PS3) in Arabidopsis and tomato. Five members of this family were identified within the Arabidopsis genome. The PS3 gene family shares a significant level of amino acid sequence homology with a number of ESTs in the Genbank, and glycerol-3-phosphate permases from bacteria. Different expression patterns of members of this family point to their unique roles during Pi starvation. These proteins are hypothesized to participate in transport of glycerol-3-phosphate or other sugar phosphates from cellular organelles during Pi deficiency.