Isolation of novel citrus and plum fruit promoters and their functional characterization for fruit biotechnology

Authors: DASGUPTA, KASTURI - Citrus Research Board; HOTTON, SARA - Former ARS Employee; BELKNAP, WILLIAM - Former ARS Employee; SYED, YASRA - Former ARS Employee; Dardick, Christopher - Chris; Thilmony, Roger; Thomson, James - Jim

Submitted to: BMC Biotechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/2/2020
Publication Date: 8/20/2020
Publication URL: https://handle.nal.usda.gov/10113/7077490
Citation: Dasgupta, K., Hotton, S., Belknap, W., Syed, Y., Dardick, C.D., Thilmony, R.L., Thomson, J.G. 2020. Isolation of novel citrus and plum fruit promoters and their functional characterization for fruit biotechnology. BioMed Central (BMC)Biotechnology. 20. https://doi.org/10.1186/s12896-020-00635-w.
DOI: https://doi.org/10.1186/s12896-020-00635-w

Interpretive Summary: Expression control elements (i.e. promoters) are crucial components required for the genetic engineering of plants, but relatively few well-characterized organ-specific promoters are available, particularly those that have been shown to function well in trees. We have isolated five novel promoter sequences from citrus and plum fruit trees. These novel promoters were shown to confer either fruit-specific, or fruit-preferential expression in genetically engineered tomato plants. One candidate promoter conferred strong activity only in specific fruit tissues during fruit development and ripening, but the other tested promoters, in addition to expressing strongly in fruit tissues, also conferred weaker expression activity in floral tissues and/or leaves of the transgenic plants. We expect that these novel promoters will serve as useful tools for fruit biotechnology research and applications developing novel traits in tree fruit crops in the future.

Technical Abstract: Promoters that confer expression in fruit tissues are important tools for genetic engineering of fruit quality traits, yet few fruit-specific promoters have been identified, particularly for citrus fruit development. In this study, we report five novel citrus fruit-specific/preferential promoters for genetic engineering. Additionally, we have characterized a novel fruit-preferential promoter from plum. Genes specifically expressed in fruit tissues were selected and their isolated promoter regions were fused with the GUSPlus reporter gene for evaluation in transgenic plants. Stable transformation in Micro-Tom tomato demonstrated that the candidate promoter regions exhibit differing levels of expression and with varying degrees of fruit specificity. Among the five candidate citrus promoters characterized in this study, the CitSEP promoter showed highest fruit-specific expression pattern. The CitWAX and CitJuSac promoters exhibited high fruit-preferential expression with strong activity in the fruit, weak activity in floral tissues and undetectable activity in other tissues. The CitVO1, CitUNK and PamMybA promoters, while fruit-preferential also showed consistent weak activity in leaves and other tissues.