Differential expression of the PAL gene family in rice seedlings exposed to chromium by microarray analysis

Phenylalanine ammonia-lyase (PAL) is one of the principle enzymes involved in plant's secondary metabolism. Expression of individual isogene from the PAL gene family is variable with species of plants in responses to different stresses. In this study, transcriptome analysis of the PAL gene family in rice seedlings exposed to potassium chromate Cr(VI) or chromium nitrate Cr(III) was conducted using Agilent 44K rice microarray and real-time quantitative RT-PCR. Uptake and accumulation of both Cr species by rice seedlings and their effect on PAL activity were also determined. Three days of Cr exposure led to significant accumulation of Cr in plant tissues, but majority being in roots rather than shoots. Changes of PAL activities in rice tissues were evident from both Cr treatments. Individual isogene from the rice PAL gene family was expressed differentially in response to both Cr variants. Comparing gene expression between two Cr treatments, only osPAL2 and osPAL4 genes were expressed in similar patterns. Also, gene expression pattern was inconsistent in both plant tissues. Results indicated that expression of individual isoform from the rice PAL gene family is tissue, and stimulus specific under different Cr exposure, suggesting their different detoxification strategies for decreasing or eliminating Cr stresses.