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Summary Chloroplast Unusual Positioning 1 (CHUP1) plays an important role in the chloroplast avoidance and accumulation responses in mesophyll cells. In epidermal cells, prior research showed silencingCHUP1‐induced chloroplast stromules and amplified effector‐triggered immunity (ETI); however, the underlying mechanisms remain largely unknown.CHUP1 has a dual function in anchoring chloroplasts and recruiting chloroplast‐associated actin (cp‐actin) filaments for blue light‐induced movement. To determine which function is critical for ETI, we developed an approach to quantify chloroplast anchoring and movement in epidermal cells. Our data show that silencingNbCHUP1inNicotiana benthamianaplants increased epidermal chloroplast de‐anchoring and basal movement but did not fully disrupt blue light‐induced chloroplast movement.SilencingNbCHUP1auto‐activated epidermal chloroplast defense (ECD) responses including stromule formation, perinuclear chloroplast clustering, the epidermal chloroplast response (ECR), and the chloroplast reactive oxygen species (ROS), hydrogen peroxide (H2O2). These findings show chloroplast anchoring restricts a multifaceted ECD response.Our results also show that the accumulated chloroplastic H2O2inNbCHUP1‐silenced plants was not required for the increased basal epidermal chloroplast movement but was essential for increased stromules and enhanced ETI. This finding indicates that chloroplast de‐anchoring and H2O2play separate but essential roles during ETI.
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Chloroplast quality control pathways are dependent on plastid DNA synthesis and nucleotides provided by cytidine triphosphate synthase two
Summary Reactive oxygen species (ROS) produced in chloroplasts cause oxidative damage, but also signal to initiate chloroplast quality control pathways, cell death, and gene expression. TheArabidopsis thaliana plastid ferrochelatasetwo(fc2) mutant produces the ROS singlet oxygen in chloroplasts that activates such signaling pathways, but the mechanisms are largely unknown.Here we characterize onefc2suppressor mutation and map it toCYTIDINE TRIPHOSPHATE SYNTHASE TWO(CTPS2), which encodes one of five enzymes in Arabidopsis necessary forde novocytoplasmic CTP (and dCTP) synthesis.Thectps2mutation reduces chloroplast transcripts and DNA content without similarly affecting mitochondria. Chloroplast nucleic acid content and singlet oxygen signaling are restored by exogenous feeding of the dCTP precursor deoxycytidine, suggestingctps2blocks signaling by limiting nucleotides for chloroplast genome maintenance. An investigation of CTPS orthologs in Brassicaceae showed CTPS2 is a member of an ancient lineage distinct from CTPS3. Complementation studies confirmed this analysis; CTPS3 was unable to compensate for CTPS2 function in providing nucleotides for chloroplast DNA and signaling.Our studies link cytoplasmic nucleotide metabolism with chloroplast quality control pathways. Such a connection is achieved by a conserved clade of CTPS enzymes that provide nucleotides for chloroplast function, thereby allowing stress signaling to occur.
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- PAR ID:
- 10449683
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- New Phytologist
- Volume:
- 231
- Issue:
- 4
- ISSN:
- 0028-646X
- Page Range / eLocation ID:
- p. 1431-1448
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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