PAL1 gene of the phenylpropanoid pathway increases resistance to the Cassava brown streak virus in cassava

Background
The phenylalanine ammonia lyase genes play crucial role in plant response to biotic and abiotic stresses. In this study, we characterized the role of PAL genes in increasing resistance to the Cassava brown streak virus that causes the economically important cassava brown streak disease (CBSD) on cassava in Africa.

Methods
The whole transcriptomes of eight cassava varieties differing in resistance to CBSD were obtained at 1, 5 and 8 weeks after CBSV infection.

Results
Analysis of RNA-Seq data identified the overexpression of PAL1, PAL2, cinnamic acid and two chalcone synthase genes in CBSD-resistant cassava varieties, which was subsequently confirmed by RT-qPCR. The exogenous application of Acibenzolar-S-Methyl induced PAL1 gene expression to enhance resistance in the susceptible var. Kalawe. In contrast, the silencing of PAL1 by RNA interference led to increased susceptibility of the resistant var. Kaleso to CBSD.

Conclusions
PAL1 gene of the phenylpropanoid pathway has a major role in inducing resistance to CBSD in cassava plants and its early induction is key for CBSD resistance.