Search

International audience; How do plants reduce growth when facing high salinity ? A new study provides insight into how salt stress impinges on the plant steroid hormone signaling pathway to dampen plant growth. Plants are growing in a constantly changing environment and, unlike most animals, cannot run away from adverse conditions. Instead, plants adjust their growth and development using an intricate network of internal signals to ensure completion of their life cycle. Among these, brassinosteroids (BRs), the polyhydroxylated steroid hormones of plants, have been the focus a lot of attention during the past two decades. The main actors driving the perception and signal transduction of BRs in plant cells have now been identified in the model plant Arabidopsis, mostly through intensive genetic and biochemical approaches. A complex cascade of phospho/dephosphorylation events conveys the BR signal from the cell surface to the nucleus where it culminates in the regulation of gene expression by the BRASSINAZOLE RESISTANT (BZR) family of transcription factors [1]. BZR proteins are absolutely essential to BR signaling and more generally to plant growth and development [2]. Their precise regulation in time and space is therefore central and at the node of many pathways ultimately impacting on plant growth. The best characterized regulatory mechanism targeting BZR proteins is a BR-regulated phospho/dephosphorylation coupled to a ubiquitin-mediated degradation by the 26S proteasome that has been brought to light with BZR1 and BZR2, the founding members of the BZR family. In the resting state, plant cells phosphorylate BZRs using the GSK3/SHAGGY kinase BIN2 [1]. This results in the cytosolic localization and destabilization of BZRs, thus shutting down BR genomic responses. When plant cells perceive BRs, BIN2 is inactivated and degraded [3, 4], allowing the dephosphorylation of BZRs by PP2A phosphatases [5]. Dephosphorylated BZRs in turn accumulate in the nucleus where they bind to target promoters to fire BR genomic responses [1]. Recently, additional BR-dependent and-independent mechanisms directly controlling the activity of BZR proteins

Brassinosteroids (BRs) are a group of steroid molecules perceived at the cell surface and that act as plant hormones. Since their discovery as crucial growth substances, BRs were mainly studied for their action in above ground organs and the BR signaling pathway was largely uncovered in the context of hypocotyl elongation. However, for the past two years, most of the exciting findings on BR signaling have been made using roots as a model. The Arabidopsis root is a system of choice for cell biology and allowed detailed characterization of BR perception at the cell membrane. In addition, a series of elegant articles dissected how BRs act in tissue specific manners to control root growth and development.

The past two decades of research on plant iron nutrition have completed the casting of the major transporters involved in iron uptake from the soil, long-distance transport, and intracellular distribution. Among these transporters, most of the attention was given to the root iron transporter IRT1, which plays a critical role in iron uptake from the soil and mediates transport of other non-iron metals (zinc, manganese, cobalt, cadmium) under iron-limiting conditions. As such, IRT1 is the primary determinant of iron and heavy metal homeostasis in plants.

International audience; Iron is essential for plant cell function and more specifically for photosynthesis. Plants have evolved highly efficient systems to take up iron from the soil. However, activating iron uptake is a double jeopardy: not only iron itself is toxic but iron uptake systems are poorly selective and allow the entry of other potentially toxic metals. Plants therefore tightly control iron uptake at the transcriptional and post-translational level and have evolved mechanisms to cope with the concomitant entry of toxic metals. In plant cells, iron has to be distributed to chloroplasts and mitochondria or may be stored safely in vacuole. Distinct transcriptional networks regulating uptake and intracellular distribution are being uncovered, while iron sensing mechanisms remain elusive.