A novel approach for developing resistance in rice against phloem limited viruses by antagonizing the phloem feeding hemipteran vectors

Abstract

Rice production is known to be severely affected by virus transmitting rice pests, brown planthopper (BPH) and green leafhopper (GLH) of the order hemiptera, feeding by phloem abstraction. ASAL, a novel lectin from leaves of garlic (Allium sativum) was previously demonstrated to be toxic towards hemipteran pests when administered in artificial diet as well as in ASAL expressing transgenic plants. In this report ASAL was targeted under the control of phloem-specific Agrobacterium rolC and rice sucrose synthase-1 (RSs1) promoters at the insect feeding site into popular rice cultivar, susceptible to hemipteran pests. PCR, Southern blot and C-PRINS analyses of transgenic plants have confirmed stable T-DNA integration and the transgenes were co-segregated among self-fertilized progenies. The T(0) and T(1) plants, harbouring single copy of intact T-DNA expression cassette, exhibit stable expression of ASAL in northern and western blot analyses. ELISA showed that the level of expressed ASAL was as high as 1.01% of total soluble protein. Immunohistofluorescence localization of ASAL depicted the expected expression patterns regulated by each promoter type. In-planta bioassay studies revealed that transgenic ASAL adversely affect survival, growth and population of BPH and GLH. GLH resistant T(1) plants were further evaluated for the incidence of tungro disease, caused by co-infection of GLH vectored Rice tungro bacilliform virus (RTBV) and Rice tungro spherical virus (RTSV), which appeared to be dramatically reduced. The result presented here is the first report of such GLH mediated resistance to infection by RTBV/RTSV in ASAL expressing transgenic rice plant.

Biotechnological Prospects for Engineering Insect-Resistant Plants

“…Similar partial resistance to hemipterans has also been obtained by expression of a Man-specific lectin from garlic (Allium sativum) leaves (ASA-L) in transgenic rice (Saha et al, 2006a) and a variety of other transgenic plant species. The transgenic rice plants expressing ASA-L were shown to decrease transmission of Rice tungro virus by its insect vector, presumably as a result of decreased feeding by the pest (Saha et al, 2006b). …”

Peptide Aptamers That Bind to Geminivirus Replication Proteins Confer a Resistance Phenotype to Tomato Yellow Leaf Curl Virus and Tomato Mottle Virus Infection in Tomato

“…Second, although some geminiviruses can invade mesophyll and epidermal cells (31,32), many are limited to the phloem, and all must pass through vascular tissue during systemic movement and insect vector acquisition (7). Hence, expressing the peptide aptamers under the control of a phloem-specific promoter might enhance their effectiveness (83,84). Third, A22 and A64 bind to different regions of the Rep N terminus and may act through different mechanisms.…”

What are the prospects for genetically engineered, disease resistant plants?

“…Synthetic, chimeric toxins have been developed which extend the range of these toxins to other insect groups (Mehlo et al 2005). Furthermore, as for fungi, there are examples of transgenic strategies using genes encoding other insecticidal proteins, for example lectins, which have led to resistance against these types of insects in the laboratory (Saha et al 2006;Yao et al 2003).…”