Suppression of a Phospholipase D Gene, OsPLDβ1, Activates Defense Responses and Increases Disease Resistance in Rice1[C][W][OA]

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 OsPLDα1 , OsPLDα5 , and OsPLDβ1 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, OsPLDβ1 -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 OsPLDβ1 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 OsPLDβ1 -knockdown plants. These results indicated that the OsPLDβ1 -knockdown plants spontaneously activated the defense responses in the absence of pathogen infection. Furthermore, the OsPLDβ1 -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 β 1 functions as a negative regulator of defense responses and disease resistance in rice.