Molecular Characterization of Magnesium Chelatase in Soybean [Glycine max (L.) Merr.]

Abstract

Soybean (Glycine max) seed yields rely on the efficiency of photosynthesis, which is poorly understood in soybean. Chlorophyll, the major light harvesting pigment, is crucial for chloroplast biogenesis and photosynthesis. Magnesium chelatase catalyzes the insertion of Mg2+ into protoporphyrin IX in the first committed and key regulatory step of chlorophyll biosynthesis. It consists of three types of subunits, ChlI, ChlD, and ChlH. To gain a better knowledge of chlorophyll biosynthesis in soybean, we analyzed soybean Mg-chelatase subunits and their encoding genes. Soybean genome harbors 4 GmChlI genes, 2 GmChlD genes, and 3 GmChlH genes, likely evolved from two rounds of gene duplication events. The qRT-PCR analysis revealed that GmChlI, GmChlD, and GmChlH genes predominantly expressed in photosynthetic tissues, but the expression levels among paralogs are different. In silicon promoter analyses revealed these genes harbor different cis-regulatory elements in their promoter regions, suggesting they could differentially respond to various environmental and developmental signals. Subcellular localization analyses illustrated that GmChlI, GmChlD, and GmChlH isoforms are all localized in chloroplast, consistent with their functions. Yeast two hybrid and bimolecular fluorescence complementation (BiFC) assays showed each isoform has a potential to be assembled into the Mg-chelatase holocomplex. We expressed each GmChlI, GmChlD, and GmChlH isoform in Arabidopsis corresponding mutants, and results showed that 4 GmChlI and 2 GmChlD isoforms and GmChlH1 could rescue the severe phenotype of Arabidopsis mutants, indicating that they maintain normal biochemical functions in vivo. However, GmChlH2 and GmChlH3 could not completely rescue the chlorotic phenotype of Arabidopsis gun5-2 mutant, suggesting that the functions of these two proteins could be different from GmChlH1. Considering the differences shown on primary sequences, biochemical functions, and gene expression profiles, we conclude that the paralogs of each soybean Mg-chelatase subunit have diverged more or less during evolution. Soybean could have developed a complex regulatory mechanism to control chlorophyll content to adapt to different developmental and environmental situations.

Single Nucleotide Mutagenesis of the TaCHLI Gene Suppressed Chlorophyll and Fatty Acid Biosynthesis in Common Wheat Seedlings

“…Our results indicated that the expression of TaCHLI showed the highest levels in leaves, was lower in developing seeds and stems, and was negligible in roots and anthers of SN33 ( Figure 1G). This is consistent with previous studies in cucumber (Gao et al, 2016) and soybean (Zhang et al, 2018). As a major staple food (Paux et al, 2008), the growth of wheat under field conditions is influenced by many factors, such as light and temperature.…”

“…Sequence analysis further revealed a single-nucleotide mutation in TaCHLI-7A at position 664, which changed G (in SN33) to A (in chli) ( Figure 4A). CHLI is a highly conserved protein in plants (Zhang et al, 2018). As shown in the phylogenetic tree (Figure 7), CHLI from dicots tended to cluster together, which was also observed for monocots.…”

“…Moreover, Chl content can act as a proxy for leaf photosynthetic capacity (Inoue et al, 2016;Croft et al, 2017) and is intimately related to fatty acid biosynthesis, which is likely to influence wheat seedling development strongly. As a major regulatory point of Chl biogenesis, Mg-chelatase represents an important target for the improvement of photosynthetic efficiency (Zhang et al, 2018). Hence, our studies on chli open the door to a better understanding of Chl metabolism, photosynthetic regulation, and variety improvement in common wheat.…”

“…For example, in modern maize breeding, most grain yield increases have been primarily due to improved chloroplast structure and increased solar energy absorption by Chl . Hence, Chl content is generally considered one of the major factors limiting photosynthetic efficiency (Hotta et al, 1997;Zhang et al, 2018). Solar energy capture by Chl has been known since as early as 1935 (Chlorophyll, 1935).…”

A TMT-Based Quantitative Proteome Analysis to Elucidate the TSWV Induced Signaling Cascade in Susceptible and Resistant Cultivars of Solanum lycopersicum

“…Decreased abundances of two isoforms of magnesium-chelatase and three isoforms of protochlorophyllide reductase were observed in the susceptible cultivar upon TSWV infection. Magnesium-chelatase catalyzes the first and the rate-limiting step of chlorophyll biosynthesis by inserting Mg 2+ into protoporphyrin IX [14] while protochlorophyllide reductases are involved in the conversion of protochlorophyllide to chlorophyllide, immediate precursors of chlorophyll [15]. As chlorophyll is the primary pigment involved in harvesting the sunlight, decreased abundances of these enzymes suggest overall downregulation of light reactions.…”