Modified Crosstalk between Phytohormones in Arabidopsis Mutants for PEP-Associated Proteins.

Plastid-encoded RNA polymerase (PEP) forms a multisubunit complex in operating chloroplasts, where PEP subunits and a sigma factor are tightly associated with 12 additional nuclear-encoded proteins. Mutants with disrupted genes encoding PEP-associated proteins (PAPs) provide unique tools for deciphering mutual relationships among phytohormones. A block of chloroplast biogenesis in mutants specifying highly altered metabolism in white tissues induced dramatic fluctuations in the content of major phytohormones and their metabolic genes, whereas hormone signaling circuits mostly remained functional.

Cytokinin Modulates Responses to Phytomelatonin in under High Light Stress.

Fine-tuned interactions between melatonin (MT) and hormones affected by environmental inputs are crucial for plant growth. Under high light (HL) conditions, melatonin reduced photodamage in and contributed to the restoration of the expression of the cytokinin (CK) synthesis genes , and and genes for CK signal transduction , and , , and which were downregulated by stress. However, CK signaling mutants displayed no significant changes in the expression of CK genes following HL + MT treatment, implying that a fully functional cytokinin signaling pathway is a prerequisite for MT-CK interactions.

The role of PAP4/FSD3 and PAP9/FSD2 in heat stress responses of chloroplast genes.

Chloroplasts' mechanisms of adaptation to elevated temperatures are largely determined by the gene expression of the plastid transcription apparatus. Gene disruption of iron-containing superoxide dismutase PAP4/FSD3 and PAP9/FSD2, which are parts of the DNA-RNA polymerase complex of plastids, contributed to a decrease in resistance to oxidative stress caused by the prolonged action of elevated temperatures (5 days, 30 °C). Under heat stress conditions, pap4/fsd3 and pap9/fsd2 mutants showed a decline in chlorophyll content and photosynthesis level, as measured by photosynthetic parameters, and a different amplitude of HSP gene response to heat stress.

Cytokinin-Regulated Expression of Genes and Its Implication for the Expression of Chloroplast-Encoded Genes.

Cytokinins (CKs) are known to regulate the biogenesis of chloroplasts under changing environmental conditions and at different stages of plant ontogenesis. However, the underlying mechanisms are still poorly understood. Apparently, the mechanisms can be duplicated in several ways, including the influence of nuclear genes that determine the expression of plastome through the two-component CK regulatory circuit.