Raising the production of phloretin by alleviation of by-product of chalcone synthase in the engineered yeast

Phloretin is an important skin-lightening and depigmenting agent from the peel of apples. Although de novo production of phloretin has been realized in microbes using the natural pathway from plants, the efficiency of phloretin production is still not enough for industrial application. Here, we established an artificial pathway in the yeast to produce phloretin via assembling two genes of p-coumaroyl-CoA ligase(4CL) and chalcone synthase(CHS). CHS is a key enzyme which conventionally condenses a CoA-tethered starter with three molecules of malonyl-CoA to form the backbone of flavonoids. However, there was 33% of byproduct generated via CHS by condensing two molecules of malonyl-CoA during the fermentation process. Hence, we introduced a more efficient CHS and improved the supply of malonyl-CoA through two pathways;the by-product ratio was decreased from 33% to 17% and the production of phloretin was improved from 48 to 83.2 mg L^(-1). Finally, a fed-batch fermentation process was optimized and the production of phloretin reached 619.5 mg L^(-1), which was 14-fold higher than that of the previous studies. Our work established a platform for the biosynthesis of phloretin from the low-cost raw material 3-(4-hydroxyphenyl) propanoic acid and also illustrated the potential for industrial scale bio-manufacturing of phloretin.

Plastid engineering with an efficient RNAi delivery system based on bacteriophage MS2 virus-like particles enhances plant resistance to cotton bollworm

Dear Editor,RNA-based pesticides are approaching the market,offering great potential to control agricultural pests such as the coleopteran insect Diabrotica virgifera virgifera(Head et al.,2017).However,application to lepidopteran pests has been hampered by their inconsistent response to RNA interference(RNAi).As a notorious lepidoptera pest,Helicoverpa armigera feeds on over 300 species of host plants(Fu et al.,2022).Although transgenicplants expressingdouble-stranded RNAs or microRNAs that target essential insect genes can inhibit the growth of larvae,complete protection of the plants and efficient killing of this insect have not been achieved(Bally et al.,2020;Chung et al.,2021;Li et al.,2023).The relatively low RNAi efficiency in lepidopterans is mainly attributable to the degradation and intracellular sequestration of double-stranded RNA(Shukla et al.,2016;Zhu and Palli,2020).To overcome these obstacles and improve RNAi efficiency in H.armigera,we attempted to deliver RNAi molecules using a bacteriophage MS2 virus-like particle(VLP)-based delivery system(Wang et al.,2016).