Short-Term Magnesium Deficiency Triggers Nutrient Retranslocation in Arabidopsis thaliana

Abstract

Magnesium (Mg) is essential for many biological processes in plant cells, and its deficiency causes yield reduction in crop systems. Low Mg status reportedly affects photosynthesis, sucrose partitioning and biomass allocation. However, earlier physiological responses to Mg deficiency are scarcely described. Here, we report that Mg deficiency in Arabidopsis thaliana first modified the mineral profile in mature leaves within 1 or 2 days, then affected sucrose partitioning after 4 days, and net photosynthesis and biomass production after 6 days. The short-term Mg deficiency reduced the contents of phosphorus (P), potassium, manganese, zinc and molybdenum in mature but not in expanding (young) leaves. While P content decreased in mature leaves, P transport from roots to mature leaves was not affected, indicating that Mg deficiency triggered retranslocation of the mineral nutrients from mature leaves. A global transcriptome analysis revealed that Mg deficiency triggered the expression of genes involved in defence response in young leaves.

Combined analyses of translatome and transcriptome in Arabidopsis reveal new players responding to magnesium deficiency

“…In group V, genes involved in ubiquitin protein ligase binding were significantly down‐regulated at the translational level (Figure 3C). When compared with other published transcriptome data sets from samples subjected to Mg deficiency for various periods, we found that 18 of the 31 DEGs at the translational level (64.5%) were also transcriptionally regulated at least 5 d after treatment (Hermans et al, 2010a, 2010b; Ogura et al, 2020), and only two were regulated within 3 d after Mg deficiency. These results indicate that translation responses to Mg treatment are quicker and more sensitive.…”

“…There are 443 genes that are regulated by HY5 (Lee et al, 2007; Toledo‐Ortiz et al, 2014; Burko et al, 2020). After checking them against a list of published Mg deficiency responsive genes, including genes identified in this study, almost half of the 443 HY5 ‐regulated genes were regulated by Mg deficiency (Figure S6A; Hermans et al, 2010a, 2010b; Ogura et al, 2020). Among them, four chlorophyll synthesis‐related genes, Light‐Harvesting complex 4 ( LHCA4 ), Protochlorophyllide oxidoreductase ( PORC ), Genome uncoupled 5 ( GUN5 ), and Phytoene synthase ( PSY ), were down‐regulated at the transcriptional level by Mg deficiency treatment (Hermans et al, 2010b; Ogura et al, 2020), consistent with the previous report that HY5 regulates chlorophyll synthesis under dark/light transition and low/high temperature change (Toledo‐Ortiz et al, 2014).…”

“…After checking them against a list of published Mg deficiency responsive genes, including genes identified in this study, almost half of the 443 HY5 ‐regulated genes were regulated by Mg deficiency (Figure S6A; Hermans et al, 2010a, 2010b; Ogura et al, 2020). Among them, four chlorophyll synthesis‐related genes, Light‐Harvesting complex 4 ( LHCA4 ), Protochlorophyllide oxidoreductase ( PORC ), Genome uncoupled 5 ( GUN5 ), and Phytoene synthase ( PSY ), were down‐regulated at the transcriptional level by Mg deficiency treatment (Hermans et al, 2010b; Ogura et al, 2020), consistent with the previous report that HY5 regulates chlorophyll synthesis under dark/light transition and low/high temperature change (Toledo‐Ortiz et al, 2014). To investigate whether these chlorophyll synthesis genes were regulated by HY5 under Mg deficiency, we conducted quantitative reverse‐transcription polymerase chain reaction (qRT‐PCR) to analyze the transcript levels of these genes in the hy5 mutant treated for 7 d under Mg deficiency condition.…”

“…Different species require different time lengths to show responses to Mg Deficiency—from increased sucrose accumulation to disrupted photosynthetic activity and even to noticeable morphological phenotypes (Cakmak et al, 1994; Hermans et al, 2004; Hermans and Verbruggen, 2005; Cakmak and Kirkby, 2008). The transcript level of the gene encoding Chlorophyll a/b binding protein 2 ( CAB2 ) was down‐regulated as early as 3 d after Mg deficiency (Ogura et al, 2020), which was prior to the remarkably decreased chlorophyll content under Mg deficiency (Hermans and Verbruggen, 2005). Mg deficiency also results in the generation of reactive oxygen species (ROS) and then cell damage due to excess photosynthetic electrons (Cakmak and Kirkby, 2008).…”

“…Genes responsive to Mg deficiency have been analyzed at the transcriptional level in root and shoot by microarray and RNA‐seq from 4 h after treatment to 8 d after treatment (Hermans et al, 2010a; Ogura et al, 2020). However, these studies provided little genetic evidence to support their physiological association with Mg deficiency.…”