A proximal upstream sequence controls tissue-specific expression of Lem2, a salicylate-inducible barley lectin-like gene

The lemma and palea (lemma/palea), which form the husk of barley ( Hordeum vulgare L.) seeds, constitutively express high levels of defense-related genes, relative to leaves [ Abebe et al. ( 2004) Crop Sci 44: 942 - 950]. One of these genes, Lem2, is expressed mainly in the lemma/palea and coleoptile and is strongly upregulated by salicylic acid ( SA) and its functional analog 2,6-dichloroisonicotinic acid. Induction by SA was rapid, occurring within 4 h of treatment. However, Lem2 is not responsive to methyl jasmonate (MeJA) or wounding and is downregulated by drought, dehydration, and abscisic acid. These results suggest that Lem2 is involved in systemic acquired resistance. Sequence analysis showed that LEM2 is a jacalin-related lectin (JRL)-like protein with two domains. Consistent with northern and western blot data, transient expression analyses using Lem2:: gfp constructs showed strong expression in lemmas and a trace expression in leaves. Successive 5' deletions of the 1,414 bp upstream region gradually weakened promoter strength, as measured by real-time PCR. Promoter deletion studies also revealed that the - 75/+ 70 region ( containing the TATA box, 5' UTR, and a SA-response element) determines tissue specificity and that the distal promoter region simply enhances expression. 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.