Wilkens, A. | Search bioRxiv

bioRxiv2023

ATML1 Regulates the Differentiation of ER Body-containing Large Pavement Cells in Rosette Leaves of Brassicaceae Plants

Endoplasmic reticulum (ER)-derived organelles, ER bodies, participate in the defense against herbivores in Brassicaceae plants. ER bodies accumulate {beta}-glucosidases, which hydrolyse specialized thioglucosides known as glucosinolates to generate bioactive substances. In Arabidopsis thaliana, the leaf ER (LER) bodies are formed in large pavement cells, which are found in the petioles, margins, and blades of rosette leaves. However, the regulatory mechanisms involved in establishing large pavement cells are unknown. Here, we show that the ARABIDOPSIS THALIANA MERISTEM L1 LAYER (ATML1) transcription factor regulates the formation of LER bodies in large pavement cells of rosette leaves. Overexpression of ATML1 enhanced the expression of LER body-related genes and the number of LER body-containing large pavement cells, whereas its knockout resulted in opposite effects. ATML1 enhances endoreduplication and cell size through LOSS OF GIANT CELLS FROM ORGANS (LGO). Although the overexpression and knockout of LGO affected the appearance of large pavement cells in Arabidopsis, the effect on LER body-related gene expression and LER body formation was weak. LER body-containing large pavement cells were also found in Eutrema salsugineum, another Brassicaceae species. Our results demonstrate that ATML1 establishes large pavement cells to induce LER body formation in Brassicaceae plants, contributing to the defense against herbivores.

plant biology↗

bioRxiv2023

Arabidopsis MEB3 functions as a vacuolar transporter to regulate iron accumulation in roots

Iron is an essential nutrient for plant photosynthesis and development, but excess iron leads to stress. After absorption from the soil, plants store iron in roots and distribute it to shoots via long-distance transport. Vacuole serves as the iron storage organ in root cells, maintaining cellular iron homeostasis, and vacuolar iron transporter (VIT) family proteins have been identified as plant vacuolar iron transporters. However, the contribution of vacuolar iron transporters to the overall iron homeostasis of plants is not fully understood. Here, we show that MEMBRANE PROTEIN OF ER BODY 3 (MEB3), a VIT family member, is a vacuolar iron transporter involved in root-shoot iron distribution in Arabidopsis thaliana. Heterologous expression of Arabidopsis MEB3 in yeast restored the iron resistance phenotype of the vacuolar iron transporter deficient mutant ccc1, indicating that MEB3 regulates iron transport. In Arabidopsis, MEB3 was expressed in almost all tissues, albeit to higher levels in roots and seedlings, and the MEB3 protein localized to the tonoplast. At low iron concentration, meb3 knockout mutants accumulated less iron in shoots, suggesting that MEB3 promotes iron accumulation in shoots. Consistently, meb3 mutants exhibited reduced growth compared with the wild type upon transfer to iron-deficient medium. However, at high iron concentration, meb3 mutants accumulated more iron in shoots and less iron in roots than the wild type, indicating the impairment of proper iron distribution in meb3 mutants. These findings demonstrate that MEB3 is a vacuolar iron transporter involved in root-to-shoot iron distribution.

plant biology↗