Transcript profiling leads to biomarker identification for agarwood resin-loaded Aquilaria malaccensis

Key message The expression of terpenoid and defense response genes elevated during agarwood formation. TDFs obtained from these genes can serve as biomarkers to distinguish resin-loaded Aquilaria plant from healthy plants. Agarwood develops in a fraction of the wild Aquilaria population as a result of natural infections and wounding in the live vascular tissues of the Aquilaria malaccensis tree. Only an expert agarwood farmer or trader can identify resin-loaded trees by detecting the hole in the trunk, but this approach is less reliable and non-scientific. This must be replaced with a scientific approach to remove ambiguity and establish a standard protocol to assess the quality and hence the economic value of the specific Aquilaria tree. Each year, a significant number of trees are harvested due to high market demand and indiscriminate felling of Aquilaria tree. This study involves a cDNA-AFLP approach for transcript profiling using 64 selective primer combinations. This produced 2760 transcript-derived fragments (TDFs), of which 50 differentially expressed TDFs (DE-TDFs) were sequenced and identified. Amongst these seven were linked to terpenoid biosynthesis, one found in each LOX, abscisic acid, jasmonic acid, and defense response pathway. TDF-1-3, 5, and 6 were identified as sesquiterpene synthase, TDF-4 as a branch point enzyme, TDF-48 as a MAP kinase, TDF-47, and TDF-49 as transcription factors (TFs). To validate the cDNA-AFLP results qRT-PCR and semi-quantitative PCR was performed for 11 DE-TDFs. These DE-TDFs were expressed only in infected plants and thus can be used as a biomarker to identify and delineate economically valuable resin-containing plants.

Automated summary

The study found that the expression of terpenoid and defense response genes increases during agarwood formation, and transcript-derived fragments obtained from these genes can serve as biomarkers to distinguish resin-loaded Aquilaria plant from healthy plants. These fragments are only expressed in infected plants and can be used to identify economically valuable resin-containing plants.