Expression and Functional Analyses of the Plastid Lipid-Associated Protein CHRC Suggest Its Role in Chromoplastogenesis and Stress

Abstract

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 transientexpression 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.

The R2R3-MYB–Like Regulatory Factor EOBI, Acting Downstream of EOBII, Regulates Scent Production by Activating ODO1 and Structural Scent-Related Genes in Petunia

“…To generate transgenic EOBI-and EOBII-RNAi petunia plants, 157-and 197-bp fragments from the 39 ends of EOBI and EOBII, respectively, were obtained by PCR, using primer set 7 for EOBI and primer set 8 for EOBII. The PCR fragments were cloned into pRNA69 in sense and antisense orientations, separated by an intron, as described by Leitner-Dagan et al (2006). The constructs were then cloned into the NotI site of the binary vector pART27 and transformed into Agrobacterium strain AGLO.…”

Chromoplast Differentiation: Current Status and Perspectives

“…The observation that suppression in tomato plants of the plastoglobulin carotenoid-associated protein (CHRC) results in 30 % reduction of carotenoids in tomato fl owers provided the fi rst evidence for the role plastoglobulin chromoplast differentiation ( Leitner-Dagan et al 2006 ). Other evidence included the overexpression in tomato of a pepper plastoglobulin, fi brillin, that caused an increase in carotenoid and carotenoid-derived fl avor volatiles ( Simkin et al 2007 ).…”

Chromoplast-Specific Carotenoid-Associated Protein Appears to Be Important for Enhanced Accumulation of Carotenoids inhp1Tomato Fruits

“…The significance of the above-mentioned plastoglobulins in the sequestration and storage of carotenoids was elegantly exemplified in two studies (Leitner-Dagan et al, 2006;Simkin et al, 2007). Overexpression of a pepper fibrillin gene in tomato resulted in a 2-fold increase in carotenoid levels as well as carotenoid-derived volatiles (Simkin et al, 2007), whereas down-regulation of CHRC in tomato led to a 30% reduction of carotenoids in the flowers (Leitner-Dagan et al, 2006).…”