Role of D-type OsEUL lectins in plant development and abiotic stress response

Abstract

The PhD aimed to gain more insight into the physiological role of several lectins from rice, especially the D-type OsEULs and their importance for the abiotic stress response, in particular drought stress response. Rice is the second most produced cereal and is a model for other important cereals. The Euonymus lectin (EUL) family is a unique group of carbohydrate-binding proteins that is omnipresent in plants, implying they fulfill an important biological role for the plant. The rice (Oryza sativa) genome contains 5 functional OsEUL genes referred to as OsEULS2, OsEULS3, OsEULD1a, OsEULD1b and OsEULD2. At the start of the PhD only a few scattered reports of proteomics data suggested that at least some of the OsEULs are stress-inducible proteins, especially the D-type OsEULs. First, a broad analysis of the five OsEULs was achieved by investigating the tissue-specific expression, the subcellular localization and the stress inducibility for each of the five OsEULs. Next, it was investigated, whether overexpression of one of the OsEUL genes affects the yield or growth traits of rice plants. After a first comparative analysis between the five OsEULs from rice, the research question focused more on the role of D-type OsEULs in root development and stress responses. The promoter activity of the D-type OsEUL genes was checked in roots of GUS reporter lines subjected to different abiotic treatments. Transgenic overexpression lines for OsEULD1a and OsEULD1b yielded longer roots and shoots, and these plants were more sensitive to salt stress and drought treatment compared to wild type plants. Also, OsEULD1a and OsEULD1b overexpression lines had longer meristematic zones with more meristematic cells compared to wild type plants. Furthermore, transcriptional analyses revealed that OsEULD1a inhibited the expression of the auxin biosynthesis gene OsYUCCA1 and the ABA biosynthesis gene NCED. Lastly, putative interaction partners for OsEULD1a were identified using GFP pull down assays and mass spectrometry