Technical Abstract: Plant cytochrome P450 monooxygenases are a group of versatile redox proteins that mediate the biosynthesis of lignins, terpenes, alkaloids, and a variety of other secondary compounds which act as plant defense agents. To determine if cytochrome P450 monooxygenases are involved in defense response to Xylella fastidiosa infection, the transcriptional and posttranscriptional modification patterns of cytochrome P450 monooxygenase gene CYP736B were investigated in leaf and stem tissues of resistant and susceptible grape plants after inoculation with this pathogenic bacteria. CYP736B transcript was up-regulated in resistant plants and down-regulated in susceptible plants at 6 weeks after X. fastidiosa inoculation. However, CYP736B expression was very low in stem tissues at all evaluated times. 5’RACE and 3’RACE sequence analyses revealed that there were three candidate transcription start sites (TSS) in the upstream region and three candidate polyadenylation (PolyA) sites in the downstream region of the grape CYP736B gene. The usage frequencies of each transcription initiation site and each polyadenylation site varied depending on plant genotype, developmental stage, tissue, and treatment. Statistical analysis revealed that coordination of different 5’ transcription initiation sites and different 3’ polyadenylation sites contributed to the final determination of CYP736B pre-mRNA splicing efficiency in both PD resistant and susceptible grapevines. These results demonstrate that expression of the grape CYP736B gene is regulated developmentally and in response to Xf infection at both transcriptional and post-transcriptional levels. Multiple transcription start and polyadenylation sites as well as their interactions may contribute to regulation of grape CYP736B gene expression.