Characterization of chloroplast region rrn16-rrn23S from the tropical timber tree Cedrela odorata L. and de novo construction of a transplastomic expression vector suitable for Meliaceae trees and other economically important crops

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The forest tree Spanish cedar (Cedrela odorata L.) is well-known for its high-value timber; however, this species is attacked by the shoot borer (Hypsipyla grandella) during its early years of development, resulting in branched stems and making the plants useless for high-quality wood production. The generation of resistant varieties expressing entomotoxic proteins may be an alternative to pesticide treatments. The use of plastid transformation rather than nuclear transformation should be used because it reduces the risk of transgene dissemination by pollen. Chloroplast transformation vectors require an expression cassette flanked by homologous plastid sequences to drive plastome recombination. Thus, C. odorata plastome sequences are a prerequisite. The rrn16-rrn23 plastome region was selected, cloned, and characterized. When the sequence identity among the rrn16-rrn23 regions from C. odorata and Nicotiana tabacum was compared, 3 inDels of 240, 104, and 39 bp were found that might severely affect transformation efficiency. Using this region, a new transformation vector was developed using pUC19 as a backbone by inserting the rrn16-trnI and trnA-rrn23 sequences from C. odorata and adding 2 independent expression cassettes into the trnI-trnA intergenic region, conferring spectinomycin resistance, the ability to express the gfp reporter gene, and a site that can be used to express any other gene of interest. eng

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