MCO1 and MCO3, two putative ascorbate oxidases with ferroxidase activity, new candidates for the regulation of apoplastic iron excess in Arabidopsis

Spotlight on cytochrome b561 and DOMON domain proteins

Biotic and abiotic stresses constrain plant growth worldwide. Therefore, understanding the molecular mechanisms contributing to plant resilience is key to achieving food security. In recent years, proteins containing dopamine β-monooxygenase N-terminal (DOMON) and/or cytochrome b561 domains have been identified as important regulators of plant responses to multiple stress factors. Recent findings show that these proteins control the redox states of different cellular compartments to modulate plant development, stress responses, and iron homeostasis. In this review, we analyze the distribution and structure of proteins with DOMON and/or cytochrome b561 domains in model plants. We also discuss their biological roles and the molecular mechanisms by which this poorly characterized group of proteins exert their functions.

Natural genetic variation underlying the negative effect of elevated CO2 on ionome composition in Arabidopsis thaliana

The elevation of atmospheric CO2 leads to a decline in plant mineral content, which might pose a significant threat to food security in coming decades. Although few genes have been identified for the negative effect of elevated CO2 on plant mineral composition, several studies suggest the existence of genetic factors. Here, we performed a large-scale study to explore genetic diversity of plant ionome responses to elevated CO2, using six hundred Arabidopsis thaliana accessions, representing geographical distributions ranging from worldwide to regional and local environments. We show that growth under elevated CO2 leads to a global decrease of ionome content, whatever the geographic distribution of the population. We observed a high range of genetic diversity, ranging from the most negative effect to resilience or even to a benefit in response to elevated CO2. Using genome-wide association mapping, we identified a large set of genes associated with this response, and we demonstrated that the function of one of these genes is involved in the negative effect of elevated CO2 on plant mineral composition. This resource will contribute to understand the mechanisms underlying the effect of elevated CO2 on plant mineral nutrition, and could help towards the development of crops adapted to a high-CO2 world.

Gene Profiling of the Ascorbate Oxidase Family Genes under Osmotic and Cold Stress Reveals the Role of AnAO5 in Cold Adaptation in Ammopiptanthus nanus

The uplift of the Qinghai Tibet Plateau has led to a drastic change in the climate in Central Asia, from warm and rainy, to dry and less rainfall. Ammopiptanthus nanus, a rare evergreen broad-leaved shrub distributed in the temperate desert region of Central Asia, has survived the drastic climate change in Central Asia caused by the uplift of the Qinghai-Tibet Plateau. Ascorbate oxidase (AO) regulates the redox status of the apoplast by catalyzing the oxidation of ascorbate acid to dehydroascorbic acid, and plays a key role in the adaptation of plants to environmental changes. Analyzing the evolution, environmental response, and biological functions of the AO family of A. nanus is helpful for understanding how plant genome evolution responds to climate change in Central Asia. A total of 16 AOs were identified in A. nanus, all of which contained the ascorbate oxidase domain, most of which contained transmembrane domain, and many were predicted to be localized in the apoplast. Segmental duplication and tandem duplication are the main factors driving the gene amplification of the AO gene family in A. nanus. Gene expression analysis based on transcriptome data and fluorescence quantitative PCR, as well as enzyme activity measurements, showed that the expression levels of AO genes and total enzyme activity decreased under short-term osmotic stress and low-temperature stress, but the expression of some AO genes (AnAO5, AnAO13, and AnAO16) and total enzyme activity increased under 7 days of cold stress. AnAO5 and AnAO11 are targeted by miR4415. Further functional studies on AnAO5 showed that AnAO5 protein was localized in the apoplast. The expression of AnAO5 in yeast cells and the transient expression in tobacco enhanced the tolerance of yeast and tobacco to low-temperature stress, and the overexpression of AnAO5 enhanced the tolerance of Arabidopsis seedlings to cold stress. Our research provides important data for understanding the role of AOs in plant adaptation to environmental change.