Genome-wide analysis of the phospholipase D family in Oryza sativa and functional characterization of PLDβ1 in seed germination

Phospholipase D (PLD) plays a critical role in plant growth and development, as well as in hormone and stress responses. PLD encoding genes constitute a large gene family that are present in higher plants. There are 12 members of the PLD family in Arabidopsis thaliana and several of them have been functionally characterized; however, the members of the PLD family in Oryza sativa remain to be fully described. Through genome-wide analysis, 17 PLD members found in different chromosomes have been identified in rice. Protein domain structural analysis reveals a novel subfamily, besides the C2-PLDs and PXPH-PLDs, that is present in rice - the SP-PLD. SP-PLD harbors a signal peptide instead of the C2 or PXPH domains at the N-terminus. Expression pattern analysis indicates that most PLD-encoding genes are differentially expressed in various tissues, or are induced by hormones or stress conditions, suggesting the involvement of PLD in multiple developmental processes. Transgenic studies have shown that the suppressed expression of rice PLD beta I results in reduced sensitivity to exogenous ABA during seed germination. Further analysis of the expression of ABA signaling-related genes has revealed that PLD beta I stimulates ABA signaling by activating SAPK, thus repressing GAmyb expression and inhibiting seed germination.