Molecular, biochemical and enzymatic characterization of photorespiratory 2-phosphoglycolate phosphatase (PGLP1) in rice.

Abstract

Phosphoglycolate phosphatase (PGLP, EC3.1.3.18) is a key enzyme in photorespiration. However, genes encoding the rice photorespiratory PGLP have not yet been identified or characterized. Here, PGLP for photorespiration in rice was identified and its enzymatic properties were investigated. In order to define the function of PGLP homologs, rice PGLP mutants were constructed using CRISPR/Cas9, the transcriptional expressions were analyzed by RT-qPCR, and subcellular localizations were detected via rice protoplast transient expression analysis. Based on sequence alignment, proteins encoded by genes OsPGLP1, OsPGLP2, and OsPGLP3 in the rice genome were predicted to have PGLP activity. Subsequent experimentation showed that OsPGLP1 and OsPGLP3 are chloroplast proteins, while OsPGLP2 is localized in the cytoplasm. In rice leaves, levels of PGLP1 transcript were substantially higher than those of PGLP2 and PGLP3, whereas in roots, levels of PGLP2 transcript were higher than those of PGLP1 and PGLP3. There was no detectable PGLP activity in leaves of the OsPGLP1 mutant, which was non-viable in ambient air condition (400 ppm CO2 ) and high CO2 (4000 ppm) was unable to restore normal growth. In contrast, mutations of PGLP2 or PGLP3 did not result in visible phenotypes and the leaf PGLP activities were also unaffected It is suggested that PGLP1, encoded by Os04g0490800, is responsible for photorespiration. Furthermore, PGLP1 is a dimer with an apparent molecular mass of ca.65 kDa, and its Km is 272 μM, with a higher broad optimum pH (7.5 to 10.0) for PGLP activity than that in other higher plants.