By Bharathi Yarasi

Rice (Oryza sativa) productivity is adversely impacted by numerous biotic
and abiotic factors.
An approximate 52% of the global production of rice is lost annually owing
to the damage caused by biotic factors, of which ~21% is attributed to the
attack of insect pests.

In this paper we report the isolation, cloning and characterization of
Allium sativum leaf agglutinin (asal) gene, and its expression in elite
indica rice cultivars using Agrobacterium-mediated genetic transformation
method. The stable transgenic lines, expressing ASAL, showed explicit
resistance against major sap-sucking pests.

Results: Allium sativum leaf lectin gene (asal), coding for mannose binding
homodimeric protein (ASAL) from garlic plants, has been isolated and
introduced into elite indica rice cultivars susceptible to sap-sucking
insects, viz., brown planthopper (BPH), green leafhopper (GLH) and
whitebacked planthopper (WBPH).

Embryogenic calli of rice were co-cultivated with Agrobacterium harbouring
pSB111 super-binary vector comprising garlic lectin gene asal along with the
herbicide resistance gene bar, both under the control of CaMV35S promoter.
PCR and Southern blot analyses confirmed stable integration of transgenes
into the genomes of rice plants.

Northern and western blot analyses revealed expression of ASAL in different
transgenic rice lines. In primary transformants, the level of ASAL protein,
as estimated by enzyme-linked immunosorbent assay, varied between 0.74% and
1.45% of the total soluble proteins.

In planta insect bioassays on transgenic rice lines revealed potent
entomotoxic effects of ASAL on BPH, GLH and WBPH insects, as evidenced by
significant decreases in the survival, development and fecundity of the
insects.

Conclusion: In planta insect bioassays were carried out on asal transgenic
rice lines employing standard screening techniques followed in conventional
breeding for selection of insect resistant plants.

The ASAL expressing rice plants, bestowed with high entomotoxic effects,
imparted appreciable resistance against three major sap-sucking insects. Our
results amply demonstrate that transgenic indica rice harbouring asal
exhibit surpassing resistance against BPH, GLH and WBPH insects.

The prototypic asal transgenic rice lines appear promising for direct
commercial cultivation besides serving as a potential genetic resource in
recombination breeding.
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