Title: Developing Transgenic Citrus for Resistance to Huanglongbing and Citrus Canker Authors
|Jaynes, J -|
Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: June 10, 2010
Publication Date: N/A
Technical Abstract: Huanglongbing (HLB) and Citrus Bacterial Canker (CBC) are serious threats to citrus production, and resistant transgenic citrus is desirable. Genes for antimicrobial peptides (AMPs) with diverse promoters have been used to generate thousands of rootstock and scion transformants. D35S::D4E1 transformed rootstocks were challenged with HLB and CBC pathogens. Initial trials on multiple individual transformants were inconclusive. Some Candidatus Liberibacter asiaticus (Las) -inoculated transformed plants appeared to grow better than controls but developed HLB symptoms and Las. More active promoters are being used to enhance AMP expression. 39 AMPs were assessed in-vitro for suppressing growth of the CBC bacteria and two bacteria related to Las. The synthetic AMPs, D4E1 and D2A21, and horseshoe crab Tachyplesin (best AMP in Dawson expression vector study) were among the most active, having minimum inhibitory concentrations =1 µM. 20 new synthetic AMPs were assessed, with key Tachyplesin functional elements. Several were highly active, with negligible hemolytic activity, and will soon be inserted into citrus. Various promoters driving GUS demonstrate great diversity in gene expression, with most individuals poorly expressing, reinforcing the importance of screening and then testing replicated superior transformants. Las sequence data are being used to develop a transgenic solution for HLB-resistance, targeting a transmembrane transporter. Genes are being identified from citrus genomic data to permit transformation and resistance using citrus-only sequences. T-DNA-like border sequences from citrus have shown effectiveness in tobacco (expressing NPTII) and are being tested in citrus. High throughput evaluation of HLB resistance requires efficient assessment, and diverse approaches are being explored.