Phenylalanine ammonia lyase (PAL) contributes to the resistance of black rice against Xanthomonas oryzae pv. oryzae

Abstract

In this study, we focus on the phenylalanine ammonia lyase (PAL) as one of the possible defense factors of black rice (a black colour mutation of Oryza sativa, containing a high amount of anthocyanin and other antioxidants) against Xanthomonas oryzae pv. oryzae (Xoo), causing bacterial leaf blight of rice. Two black rice varieties namely Pari Ireng and Melik, and three white rice varieties (IRBB21, Java14, and IR64) as control were used in this study. The analysis of the resistance trait was performed by determining disease intensity (DI) and area under the disease progress curve (AUDPC). The determination of PAL activity was performed using HPLC by analyzing trans-cinnamic acid as a product of PAL enzyme by in vitro bioassay. Protein profile analysis using SDS-PAGE was also performed to compare the profile of the infected and non-infected plants. The results showed that Java 14 (positive control) has the highest AUDPC (107.59) followed by Pari Ireng (128.33), Melik (199.63), and IRBB21 (250.19). Meanwhile, IR64 has the lowest AUDPC (304.63) which was consistent as a negative control. There was a significant increase in PAL enzyme activity in Pari Ireng, Melik and Java 14 but not in IR64 and IRBB21 following Xoo infection. Those results indicated that PAL contributes to the resistance mechanism against Xoo. The distinctive protein profile (ranged from 48 to 75 kDa) was also observed between the infected and non-infected cultivar. Based on our results, Pari Ireng was classified as a resistant cultivar against Xoo.