Virus-induced gene silencing of pea CHLI and CHLD affects tetrapyrrole biosynthesis, chloroplast development and the primary metabolic network

Abstract

The first committed and highly regulated step of chlorophyll biosynthesis is the insertion of Mg(2+) into protoporphyrin IX, which is catalyzed by Mg chelatase that consists of CHLH, CHLD and CHLI subunits. In this study, CHLI and CHLD genes were suppressed by virus-induced gene silencing (VIGS-CHLI and VIGS-CHLD) in pea (Pisum sativum), respectively. VIGS-CHLI and VIGS-CHLD plants both showed yellow leaf phenotypes with the reduced Mg chelatase activity and the inactivated synthesis of 5-aminolevulinic acid. The lower chlorophyll accumulation correlated with undeveloped thylakoid membranes, altered chloroplast nucleoid structure, malformed antenna complexes and compromised photosynthesis capacity in the yellow leaf tissues of the VIGS-CHLI and VIGS-CHLD plants. Non-enzymatic antioxidant contents and the activities of antioxidant enzymes were altered in response to enhanced accumulation of reactive oxygen species (ROS) in the chlorophyll deficient leaves of VIGS-CHLI and VIGS-CHLD plants. Furthermore, the results of metabolite profiling indicate a tight correlation between primary metabolic pathways and Mg chelatase activity. We also found that CHLD induces a feedback-regulated change of the transcription of photosynthesis-associated nuclear genes. CHLD and CHLI silencing resulted in a rapid reduction of photosynthetic proteins. Taken together, Mg chelatase is not only a key regulator of tetrapyrrole biosynthesis but its activity also correlates with ROS homeostasis, primary interorganellar metabolism and retrograde signaling in plant cells.

Dynamic composition, shaping and organization of plastid nucleoids

“…On the other hand, ptDNA displays reduced compaction in plastids of the yellow leaf tissue of mutants with silencing of the CHLD (Mg chelatase subunit D) and CHLI (Mg chelatase subunit I) genes. These mutants possess thylakoids but lack grana stacks and are devoid of the photosynthetic complexes resulting in compromised photosynthesis (Luo et al, 2013). Taken together, these studies demonstrate that thylakoid formation during chloroplast development and alterations in shape and distribution of nucleoids are interconnected processes.…”

Candidate Genes for Yellow Leaf Color in Common Wheat (Triticum aestivum L.) and Major Related Metabolic Pathways according to Transcriptome Profiling

“…The activity of Mg-chelatase has essential regulatory roles in Chl biosynthesis and chloroplast development in higher plants. For example, in peas, the virus-induced gene silencing of CHLI and CHLD yields plants with yellow leaf phenotypes and reduced Mg-chelatase activities, as well as lower Chl accumulation correlated with undeveloped thylakoid membranes [ 22 ]. In addition, CHLD and CHLI silencing greatly reduces the levels of photosynthetic proteins, as well as being correlated with reactive oxygen species homeostasis [ 22 ].…”

Functional Aspects of Silencing and Transient Expression of <i>psb</i>S in <i>Nicotiana benthamiana</i>

“…Although VIGS is efficient and reliable in solanaceous species, it has been reported for Arabidopsis as well [7]. Development of chloroplast thylakoid membranes in pea was impaired after suppression of Mg chelatase accumulation by VIGS [37]. We observed modestly higher J C values in psbS-silenced plants (Figure 3) confirming that leaves possess a limited capacity to increase energy use by noncyclic electron transport when energy dissipation by NPQ is reduced [12].…”