An engineered innate immune defense protects grapevines from Pierce disease

Abstract

We postulated that a synergistic combination of two innate immune functions, pathogen surface recognition and lysis, in a protein chimera would lead to a robust class of engineered antimicrobial therapeutics for protection against pathogens. In support of our hypothesis, we have engineered such a chimera to protect against the Gram-negative Xylella fastidiosa (Xf), which causes diseases in multiple plants of economic importance. Here we report the design and delivery of this chimera to target the Xf subspecies fastidiosa (Xff), which causes Pierce disease in grapevines and poses a great threat to the wine-growing regions of California. One domain of this chimera is an elastase that recognizes and cleaves MopB, a conserved outer membrane protein of Xff. The second domain is a lytic peptide, cecropin B, which targets conserved lipid moieties and creates pores in the Xff outer membrane. A flexible linker joins the recognition and lysis domains, thereby ensuring correct folding of the individual domains and synergistic combination of their functions. The chimera transgene is fused with an amino-terminal signal sequence to facilitate delivery of the chimera to the plant xylem, the site of Xff colonization. We demonstrate that the protein chimera expressed in the xylem is able to directly target Xff, suppress its growth, and significantly decrease the leaf scorching and xylem clogging commonly associated with Pierce disease in grapevines. We believe that similar strategies involving protein chimeras can be developed to protect against many diseases caused by human and plant pathogens.

The diversity of citrus endophytic bacteria and their interactions with Xylella fastidiosa and host plants

“…(2015) reported a novel strategy for the delivery of genetically engineered bacteria in a paratransgenic system that targets the glassy-winged sharpshooter ( Homalodisca vitripennis ), an insect vector of grapes and citrus that transmits the phytopathogen X. fastidiosa (Dandekar et al ., 2012; Rathe et al ., 2014). Using simple and inexpensive materials for bioencapsulation (Weinbreck et al ., 2010; Burgain et al ., 2011) of the engineered symbiotic bacterium, Pantoea agglomerans , they demonstrated targeting of the sharpshooter H. vitripennis under controlled conditions with an alginate hydrogel that is tuned to release its bacterial payload during xylem flow into the foregut of the insect.…”

Genomic Insights into Xylella fastidiosa Interactions with Plant and Insect Hosts

“…Recently, the introduction of a construct carrying such a peptide into transgenic grapevines, allowing its specific expression into the xylem of plants, was efficient protecting grapes against the development of Pierce's disease (Dandekar et al 2012). Other concepts leading to the constitutive expression of exogenous proteins in transgenic plants include the expression of polygalacturonase-inhibiting proteins (PGIPs) that inhibit X. fastidiosa polygalacturonase (pglA) responsible for the systemic movement of X. fastidiosa in plants (Agüero et al 2005).…”

“…Alternative, efficient, pathogen-specific, environmentally friendly, and safe approaches to control these diseases would lead to long-term sustainability of crop systems. Strategies to control X. fastidiosa currently in development, based on genomics-derived knowledge and the production of transgenic plants, focus on either the pathogen (e.g., Chatterjee et al 2008c;Dandekar et al 2012) or the vector (such as RNAi to impact insect development, not discussed here; Rosa et al 2012), or on both partners and their interactions during insect transmission . We limit our discussion to these approaches, although it should be mentioned that genomic data has provided great insights into the biology, ecology, evolution, and taxonomy of X. fastidiosa, much of which has been useful to devise other disease management strategies and for detection and quarantine purposes.…”

The PDB database is a rich source of alpha-helical anti-microbial peptides to combat disease causing pathogens

“…Genetic approaches aim at achieving the same goal of enhancing immunity through rational design of peptides 13, 47 , which are then incorporated into the genome 29, 31, 48 . Also, it is important to ensure that these non-endogenous genomic fragments have minimal effect on humans for their commercial viability 32 .…”