Early PLD alpha-mediated events in response to progressive drought stress in Arabidopsis: a transcriptome analysis

Phospholipase D (PLD) has been implicated in a variety of stresses including osmotic stress and wounding. PLD alpha 1-derived phosphatidic acid interacts with ABI1 phosphatase 2C and promotes abscisic acid signalling. It has also been shown to regulate proline biosynthesis negatively. Plants with abrogated PLD alpha show insensitivity to abscisic acid (ABA) and impaired stomatal conductance. The goal in the present study was to identify early PLD alpha-mediated events in response to progressive drought stress in Arabidopsis. Water was withheld from 7-week-old Arabidopsis thaliana (Col-0) and antisense-PLD alpha 1 (anti-PLD alpha) in a controlled environment chamber. Diurnal leaf water potential (LWP) and photosynthesis measurements were recorded five and three times a day, respectively. Quantitative reverse transcription-polymerase chain reaction (qRT-PCR) and microarray analyses were conducted using RNA from shoots collected at the fourth LWP time point on the ninth day after stress imposition. Anti-PLD alpha experienced severe water stress (-1.28 MPa) at the same time period that Col-0 experienced less water stress (-0.31 MPa). Diurnal LWP measurements showed that anti-PLD alpha had a lower LWP than Col-0 in both control and drought-stress conditions. Photosynthesis was also more affected in anti-PLD alpha than in Col-0. Anti-PLD alpha plants recovered fully following rehydration after 10 d of stress. qRT-PCR revealed up to 18-fold lower values for PLD alpha transcripts in stressed anti-PLD alpha plants when compared with stressed Col-0. Microarray expression profiles revealed distinct gene expression patterns in Col-0 and anti-PLD alpha. No differences in gene expression were detected between the two genotypes in the absence of drought stress. ROP8, PLD delta, and lipid transfer proteins were among the differentially expressed genes between the two genotypes.