Plant low-molecular-weight phospholipase A2s (PLA2s) are structurally related to the animal secretory PLA2s and are present as a family of isoforms in rice (Oryza sativa)

Recently, we purified to homogeneity and characterized a low-molecular-weight calcium-dependent phospholipase A(2) (PLA(2)) from developing elm seed endosperm. This represented the first purified and characterized PLA(2) from a plant tissue. The full sequences of two distinct but homologous rice (Oryza sativa) cDNAs are given here. These encode mature proteins of 119 amino acids (PLA(2)-I, preceded by a 19 amino acid signal peptide) and 128 amino acids (PLA(2)-II, preceded by a 25 amino acid signal peptide), and were derived from four expressed sequence tag (EST) clones. Both proteins were homologous to the N-terminal amino acid sequence of the elm PLA(2). They contained twelve conserved cysteine residues and sequences that are likely to represent the Ca2+-binding loop and active-site motif, which are characteristic of animal secretory PLA(2)s. A soluble PLA(2) activity was purified 145 000-fold from green rice shoots. This had the same biochemical characteristics as the elm and animal secretory PLA(2)s. The purified rice PLA(2) consisted of two proteins, with a molecular weight of 12 440 and 12 920, that had identical N-terminal amino acid sequences. This sequence was different from but homologous to the PLA(2)-I and PLA(2)-II sequences. Taken together, the results suggest that at least three different low-molecular-weight PLA(2)s are expressed in green rice shoots. Southern blot analysis suggested that multiple copies of such genes are likely to occur in the rice and in other plant genomes.