Submitted to: Planta
Publication Type: Peer reviewed journal
Publication Acceptance Date: 10/12/2004
Publication Date: 1/1/2005
Citation: Abebe, T., Skadsen, R.W., Kaeppler, H.F. 2005. Molecular characterization of lem2, a novel tissue-specific and defense-related barley lectin gene. Planta. 221:170-183. Interpretive Summary: Little is known about the mechanisms by which fungi infect cereal seeds and about host resistance mechanisms. We have cloned a unique gene, Lem2, and analyzed its expression in barley lemmas and paleas, the rigid leaf-like organs that eventually form the seed husk. The gene that encodes the LEM2 protein is activated very rapidly after the application of salicylic acid. This is usually an indication that the gene encodes an antifungal protein. This role will be explored in future studies. The LEM2 protein is produced in the soft interior cells of the lemma and palea. LEM2 belongs to a class of proteins that have the ability to bind the carbohydrates found on the exterior cell walls of fungi. Therefore, we propose that this protein binds to invading fungal pathogens and slows their spread within the lemma and palea. Since the Lem2 gene is found in the Morex cultivar of barley but not in many other common cultivars, it may be possible to use this gene as a molecular marker in breeding programs for disease resistance. Also, it will lead to methods for targeting the expression of other antifungal genes to these organs. This will ultimately benefit the malting and brewing industries and farmers who grow malting barleys. In addition, the results may also have the same application in wheat.
Technical Abstract: The lemma and palea (lemma/palea) of barley (Hordeum vulgare) constitutively express high levels of defense-related genes, relative to flag leaves. We have characterized a novel lemma-, palea-, and coleoptile-specific gene, Lem2, that is inducible by salicylic acid (SA) and 2,6-dichloroisonicotinic acid (INA). Induction by SA was rapid, occurring within 4 h of treatment. However, Lem2 was not responsive to methyl jasmonate (MeJA) or wounding. Therefore, it is not involved in the MeJA-dependent defense response. Taken together, these results suggest that Lem2 is involved in systemic acquired resistance (SAR). Moreover, Lem2 was down regulated by drought, dehydration, and ABA and is unlikely to have a role in water stress. LEM2 contains two jacalin-like lectin domains. Therefore, LEM2 may bind to glycoconjugates on the surfaces of pathogens and slow infection. Immunolocalization studies showed that LEM2 accumulates only in the mesophyll and bundle sheath cells of the lemma and palea. LEM2 could prevent colonization of the vascular bundle and spreading of pathogens into the kernel. Southern analysis indicated that Morex barley has at least three copies of the Lem2 gene arranged in tandem on chromosome 5 (1H) Bin 02, near the short arm telomere. Lem2 is not present in the barley cultivars Steptoe, Harrington, Golden Promise, and Q21861.