Expression and functional analyses of the plastid lipid-associated protein CHRC suggest its role in chromoplastogenesis and stress.
Chromoplastogenesis during flower development and fruit ripening involves the dramatic overaccumulation of carotenoids sequestered into structures containing lipids and proteins called plastid lipid-associated proteins (PAPs). CHRC, a cucumber (Cucumis sativus) PAP, has been suggested to be transcriptionally activated in carotenoid-accumulating flowers by gibberellin (GA). Mybys, a MYB-like trans-activator identified here, may represent a chromoplastogenesis-related factor: Its expression is flower specific and parallels that of ChrC during flower development; moreover, as revealed by stable ectopic and transient-expression assays, it specifically trans-activates ChrC promoter in flowers accumulating carotenoids and flavonoids. A detailed dissection of ChrC promoter revealed a GA-responsive element, gacCTCcaa, the mutation of which abolished ChrC activation by GA. This cis-element is different from the GARE motif and is involved in ChrC activation probably via negative regulation, similar to other GA-responsive systems. The GA responsiveness and MYBYS floral activation of the ChrC promoter do not overlap with respect to cis-elements. To study the functionality of CHRC, which is activated in vegetative tissues similar to other PAPs by various biotic and abiotic stresses, we employed a tomato (Lycopersicon esculentum) plant system and generated RNAi-transgenic lines with suppressed LeCHRC. Transgenic flowers accumulated approximately 30% less carotenoids per unit protein than controls, indicating an interrelationship between PAPs and flower-specific carotenoid accumulation in chromoplasts. Moreover, the transgenic LeCHRC-suppressed plants were significantly more susceptible to Botrytis cinerea infection, suggesting CHRC's involvement in plant protection under stress conditions and supporting the general, evolutionarily preserved role of PAPs.
Leitner-Dagan
Yael
Y
Robert H. Smith Institute of Plant Sciences and Genetics in Agriculture, Hebrew University of Jerusalem, Rehovot 76100, Israel.
Ovadis
Marianna
M
Shklarman
Elena
E
Elad
Yigal
Y
Rav David
Dalia
D
Vainstein
Alexander
A
D000222:Adaptation, Physiological; D000595:Amino Acid Sequence; D001483:Base Sequence; D020171:Botrytis / Q000502:physiology; D002338:Carotenoids / Q000378:metabolism; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D018553:Cucumis sativus / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D035264:Flowers / Q000378:metabolism*; D018506:Gene Expression Regulation, Plant; D005875:Gibberellins / Q000502:physiology; D018551:Solanum lycopersicum / Q000382:microbiology / Q000502:physiology; D008969:Molecular Sequence Data; D010935:Plant Diseases; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D030821:Plants, Genetically Modified / Q000382:microbiology / Q000502:physiology; D018087:Plastids / Q000502:physiology*; D011401:Promoter Regions, Genetic; D034622:RNA Interference
C104174:CHRC protein, Cucumis sativus; D002352:Carrier Proteins; D005875:Gibberellins; D010940:Plant Proteins; D002338:Carotenoids