Differential expression of a phenylalanine ammonia-lyase gene, OsPAL4, in bacterial blight-susceptible and Xa21-mediated resistant indica rice cultivars

Abstract

Most agronomically important traits, including resistance against pathogens, are controlled by quantitative trait loci (QTL). Identifi-
cation of genes involved in QTL-based disease resistance is essential for breeding for cultivars exhibiting stably high resistance to

invading pathogens. Several defense-related genes have been successfully used as potential indicators and contributors to QTL-
based resistance against these devastating rice diseases. In this study, the researchers examined the expression of OsPAL4, a

phenylalanine ammonia-lyase (PAL) gene, in BB-susceptible Thai indica rice cultivar RD47 and its improved BB-resistant progenies
BC3F3 (Xa21/Xa21) inoculated with Xanthomonas oryzae pv. oryzae (Xoo). Based on the results, OsPAL4 was expressed both in the
Thai indica cultivar RD47 and BC3F3 lines. Nucleotide sequence analysis also confirmed that the partial cDNA sequence of OsPAL4

from these rice samples showed 100% nucleotide sequence similarity to the OsPAL4 nucleotide sequence in IR64. Meanwhile, ex-
pression analysis of OsPAL4 under BC3F3 inoculation showed that the gene was induced as early as one-hour post inoculation in

BC3F3 lines. Also, its expression increased at two-hour post inoculation. No sign of gene upregulation was observed in BC3F3 lines
after the two-hour post inoculation. In RD47, the expression of OsPAL4 was induced after two-hour post inoculation and is disposed to
increase again after 6 to 24-hour post inoculation. The findings suggest that OsPAL4 is induced by Xoo inoculation thereby indicating
its potential activity in the earlier responses of rice against invading pathogens.