Suppression of a Phospholipase D Gene, OsPLDβ1, Activates Defense Responses and Increases Disease Resistance in Rice

Phospholipase D (PLD) plays an important role in plants, including responses to abiotic as well as biotic stresses. A survey of the rice (Oryza sativa) genome database indicated the presence of 17 PLD genes in the genome, among which OsPLD alpha 1, OsPLD alpha 5, and OsPLD beta 1 were highly expressed in most tissues studied. To examine the physiological function of PLD in rice, we made knockdown plants for each PLD isoform by introducing gene-specific RNA interference constructs. One of them, OsPLD beta 1-knockdown plants, showed the accumulation of reactive oxygen species in the absence of pathogen infection. Reverse transcription-polymerase chain reaction and DNA microarray analyses revealed that the knockdown of OsPLD beta 1 resulted in the up-/down-regulation of more than 1,400 genes, including the induction of defense-related genes such as pathogenesis-related protein genes and WRKY/ERF family transcription factor genes. Hypersensitive response-like cell death and phytoalexin production were also observed at a later phase of growth in the OsPLD beta 1-knockdown plants. These results indicated that the OsPLD beta 1-knockdown plants spontaneously activated the defense responses in the absence of pathogen infection. Furthermore, the OsPLD beta 1-knockdown plants exhibited increased resistance to the infection of major pathogens of rice, Pyricularia grisea and Xanthomonas oryzae pv oryzae. These results suggested that OsPLD beta 1 functions as a negative regulator of defense responses and disease resistance in rice.