Photosynthesis of Root Chloroplasts Developed in Arabidopsis Lines Overexpressing GOLDEN2-LIKE Transcription Factors

Abstract

In plants, genes involved in photosynthesis are encoded separately in nuclei and plastids, and tight cooperation between these two genomes is therefore required for the development of functional chloroplasts. Golden2-like (GLK) transcription factors are involved in chloroplast development, directly targeting photosynthesis-associated nuclear genes for up-regulation. Although overexpression of GLKs leads to chloroplast development in non-photosynthetic organs, the mechanisms of coordination between the nuclear gene expression influenced by GLKs and the photosynthetic processes inside chloroplasts are largely unknown. To elucidate the impact of GLK-induced expression of photosynthesis-associated nuclear genes on the construction of photosynthetic systems, chloroplast morphology and photosynthetic characteristics in greenish roots of Arabidopsis thaliana lines overexpressing GLKs were compared with those in wild-type roots and leaves. Overexpression of GLKs caused up-regulation of not only their direct targets but also non-target nuclear and plastid genes, leading to global induction of chloroplast biogenesis in the root. Large antennae relative to reaction centers were observed in wild-type roots and were further enhanced by GLK overexpression due to the increased expression of target genes associated with peripheral light-harvesting antennae. Photochemical efficiency was lower in the root chloroplasts than in leaf chloroplasts, suggesting that the imbalance in the photosynthetic machinery decreases the efficiency of light utilization in root chloroplasts. Despite the low photochemical efficiency, root photosynthesis contributed to carbon assimilation in Arabidopsis. Moreover, GLK overexpression increased CO₂ fixation and promoted phototrophic performance of the root, showing the potential of root photosynthesis to improve effective carbon utilization in plants.

Suppression of Photosynthetic Gene Expression in Roots Is Required for Sustained Root Growth under Phosphate Deficiency

“…11). A similar phenomenonwas observed for Arabidopsis GLK OX lines in whose roots photosynthesis is activated (Waters et al, 2009;Kobayashi et al, 2013). When these lines grew under normal conditions, their root growth did not differ from that of the wild type (Fig.…”

“…In both GLK overexpressing (OX) lines, the thylakoid membrane network develops in root plastids, and photosynthesis is activated in the roots (Kobayashi et al, 2013). We grew the two GLK OX lines on P+ and Pmedium.…”

Light piping driven photosynthesis in the soil: Low-light adapted active photosynthetic apparatus in the under-soil hypocotyl segments of bean (Phaseolus vulgaris)

“…These are general characteristics of plants grown under low-light conditions [11,37,17]. The Chl-protein composition observed in the US-1 region showed similarity to that of greening roots [38], but the organization of the antennae was normal in the bean hypocotyl according to the fluorescence emission spectra of the different hypocotyl regions [7]. The reorganization of thylakoid complexes, i.e.…”

Identification and cloning of GOLDEN2-LIKE1 (GLK1), a transcription factor associated with chloroplast development in Brassica napus L.

“…Moreover, many genes encoding products that positively regulate the expression of genes involved in photosynthesis or plastid differentiation have been identified. For example, the Lhca and Lhcb gene family encodes the light-harvesting chlorophyll a/b-binding proteins LHCI and LHCII, which capture light energy and transfer it to chlorophylls (Chls) in the core reaction centers of photosystems I and II (PSI and PSII) (Kobayashi et al, 2013). chlorophyll b binding proteins of the lightharvesting complexes (LHCB) and the small subunit of ribulose-1,5-bisphosphate carboxylase (SSU) modulate photosynthesis-related nuclear gene expression (Kakizaki et al, 2009), and HY5 and its homologs HYH and HFR1/REP1/RSF1 affect the expression of photosynthesisrelated genes and proplastid differentiation (Fairchild et al, 2000;Spiegelman et al, 2000;McCormac and Terry, 2002;Wang et al, 2016), which is the key target of the COP1/SPA complex (Xu et al, 2015).…”

“…The GOLDEN2-LIKE (GLK) transcription factors directly influence the transcription of genes related to photosynthesis, and GLK1 plays a crucial role in normal chloroplast development in many plant species, including Arabidopsis thaliana, Zea mays (maize), Oryza sativa (rice), Solanum lycopersicum (tomato), and the moss Physcomitrella patens (Rossini et al, 2001;Waters et al, 2008Waters et al, , 2009Nakamura et al, 2009;Kobayashi et al, 2013;Nguyen et al, 2014). GLK genes belong to the GARP (G, G2; AR, ARR; P, Psr1) superfamily, which contains two homologs of GLK genes (GLK1 and GLK2) (Riechmann et al, 2000).…”