Engineering sorghum for higher 4-hydroxybenzoic acid content

Lignocellulosic biomass represents a renewable source of sugars for the manufacturing of bioproducts such as biofuels. The high cost associated with deconstruction of plant biomass to simple sugars remains one of the challenges preventing the deployment of economically sustainable advanced bioproducts. The accumulation in-planta of value-added coproducts such as platform chemicals can improve the economics of biofuels. Among other crops, sorghum is an ideal bioenergy feedstock due to its low input requirements, efficient nitrogen recycling, and high water use efficiency and biomass yields. In this work, we engineered sorghum to overproduce the valuable chemical 4-hydroxybenzoic acid (4-HBA) by co-expressing plastid-targeted versions of Escherichia coli chorismate pyruvate-lyase (UbiC) and feedback-resistant 3-deoxy-D-arabino-heptulonate-7-phosphate synthase (AroG*). Two independent lines containing the dual aroG*-ubiC construct were selected for characterization in the T2 generation. Using liquid chromatography-mass spectrometry, analysis of methanolic extracts obtained from biomass samples revealed an accumulation of 4-HBA in the two transgenic lines (corresponding to 1.56% and 1.72% dry weight, respectively), with 4-HBA glucose conjugates representing major forms. Measurements of biomass composition and several agronomic traits showed no significant difference between transgenic and wild-type control plants grown under controlled environment. This work demonstrates the transferability of the ubiC engineering approach to sorghum; generated lines will be useful to assess the agronomic performance of modified 4-HBA-rich sorghum under natural conditions.