Model of how plants sense zinc deficiency

Abstract

Plants are capable of inducing a range of physico-chemical and microbial modifications of the rhizosphere which can mobilize mineral nutrients or prevent toxic elements from entering the roots. Understanding how plants sense and adapt to variations in nutrient availability is essential in order to develop plant-based solutions addressing nutrient-use-efficiency and adaptation to nutrient-limited or -toxic soils. Recently two transcription factors of the bZIP family (basic-region leucine zipper) have been identified in Arabidopsis and shown to be pivotal in the adaptation response to zinc deficiency. They represent not only the first regulators of zinc homeostasis identified in plants, but also a very promising starting-point that can provide new insights into the molecular basis of how plants sense and adapt to the stress of zinc deficiency. Considering the available information thus far we propose in this review a putative model of how plants sense zinc deficiency.

Phylogenetic analysis of F-bZIP transcription factors indicates conservation of the zinc deficiency response across land plants

“…affecting protein stability, dimerization, subcellular localization, DNA binding activity or transactivation function) needs to be addressed. In particular, the hypothesized role for the His/Cys-rich motif in the direct regulation by zinc of F-bZIP TFs is yet to be determined 35, 52 .…”

“…Within the A. thaliana F subfamily, the AtbZIP19 and AtbZIP23 share higher amino acid sequence identity when compared to AtbZIP24. However, all three F bZIP proteins display a characteristic His/Cys-rich motif which is a signature of this bZIP subfamily 24, 35 .…”

Structural Determinants Allowing Transferase Activity in SENSITIVE TO FREEZING 2, Classified as a Family I Glycosyl Hydrolase

“…Free Mg 2ϩ concentrations are lower than this and have been measured as low as 0.4 mM (93). In comparison, Ca 2ϩ and Zn 2ϩ concentrations are estimated to be nano-or even picomolar (94,95). Monovalent cations can be present at much higher levels, and K ϩ concentrations alone are estimated at 55-60 mM (96).…”

Advances in the molecular understanding of biological zinc transport

“…11-Base-pair ZREs (zincresponsive elements) that mediate response to zinc deficiency are known for baker's yeast, 79 and in plants, zinc-deficiency response elements (ZDREs) have been identified recently. 80 In addition, putative MREs have also been predicted in plants, albeit without the associated protein(s) that recognise them. 81 The sensor proteins from different phyla also differ significantly from each other.…”

“…81 The sensor proteins from different phyla also differ significantly from each other. In mammals and insects, MREs with the core consensus sequence TGCRCNC (N = any nucleotide, R = A or G) are recognised by the zinc finger protein MTF-1; 74 the 10-base-pair plant ZDREs are recognised by basic leucine zipper (bZIP) proteins, 80 and in bacteria, a variety of sensor families recognise different inverted repeat sequences. 82 Zinc sensing by transcriptional regulators almost always involves allostery: 73,77 in the most simple cases, the binding of zinc elicits a conformational change, or stabilises a particular protein conformation, which increases or decreases the affinity to DNA.…”