Transcriptional behavior of EUL-related rice lectins toward important abiotic and biotic stresses

The rice genome encodes several genes for putative carbohydrate-binding proteins belonging to the family of Euonymus related lectins (EULs). This lectin family was discovered recently and evidence shows that the expression of these proteins is subject to multiple environmental stresses. In this study, quantitative reverse transcription PCR (qRT-PCR) was conducted on rice seedlings exposed to various abiotic (150mM NaCl, 100mM mannitol, and 100μM abscisic acid (ABA)) and biotic (Xanthomonas oryzae pv. oryzae and Magnaporthe oryzae) stresses to compare the transcriptional behavior of the EULs and a known stress related lectin Orysata belonging to the family of jacalin-related lectins. All EUL transcripts were strongly up-regulated after ABA and NaCl treatments in the roots whereas the overall expression level was generally lower and more variable in the shoots. Moreover, all abiotic stresses induced Orysata in both tissues except for mannitol treatment which failed to show an effect in the roots. Orysata also strongly accumulated after X. oryzae pv. oryzae infection, as were various D-type EUL lectins. In contrast, some of the EUL proteins, including OrysaEULS3, OrysaEULD1A and OrysaEULD2, as well as Orysata were significantly down-regulated upon M. oryzae attack, suggesting fungal manipulation of these genes. Collectively, our results clearly show that rice expresses multiple carbohydrate-binding proteins in response to a wide variety of abiotic and biotic stress conditions. We hypothesize that the Euonymus related proteins fulfill a prominent role in sensing and responding to multiple environmental cues.