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Antagonistic action of PHYA and PHYB is involved in FR-dependent leaf senescence in Arabidopsis accessions

ABSTRACT: Sensing environmental changes is important for survival of plants, as sessile organisms, in habi-tat. Recently, latitudinal clines in leaf senescence have been reported to be influenced by tem-perature and photoperiod. However, the relationship of light quality with latitudinal response of leaf senescence is still unclear. Here, we found that Arabidopsis accessions in far-red (FR) showed a strong negative correlation of leaf senescence with the latitude of their origin. phyto-chrome A (phyA) and B (phyB) mutants showed early and delayed senescence in FR, respec-tively, suggesting that PHYA and PHYB are involved in FR-dependent leaf senescence. Tran-scriptomic analysis identified genes oppositely regulated by PHYA and PHYB, and they were mainly associated with phytohormone, temperature, and defense, suggesting their associations with FR-dependent antagonistic effects of PHYA and PHYB on leaf senescence. Among these genes, the expression of WRKY6 in Arabidopsis accessions showed the highest correlation with latitude of their origin. Consistently, wrky6 mutant exhibited delayed senescence phenotype in FR. In conclusion, we propose that PHYs-regulated genes, including WRKY6, are involved in latitudinal leaf senescence in FR and this regulatory mode may contribute to latitudinal adapta-tion by responding FR, as a piece of geographical information.

ORGANISM(S): Arabidopsis thaliana

PROVIDER: GSE103946 | GEO | 2018/09/30

REPOSITORIES: GEO

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Project description:Plant growth and development are strongly affected by light signals perceived by phytochromes (phy) and cryptochromes (cry). The physical interaction between photoreceptors and the cross-talk among downstream signalling steps creates a network of interactions in which the action of one photoreceptor depends on the status of the others. The processes modulated by phy and or cry include seed germination, seedling de-etiolation, plant body formation and flowering. Compared to the wild type the leaves of the phyB mutant are characterised by their extended petioles and pale colour. These features resemble the phenotype of normal plants grown under the low red to far-red ratios typical of dense plant canopies thus providing support to the idea that phyB plays a key role in the perception of high red to far-red ratios. The triple mutant lacking phyA cry1 and cry2 shows little differences in leaf size and shape with the wild typebut the quadruple phyA phyB cry1 cry2 mutant shows severely impaired leaf expansion. In addition to the specific effects on leaf sizeshape and pigmentation the phyB mutation accelerates flowering in the wild type background. This effect can be observed as a reduced number of days between sowing and visible flower buds (time scale) and as a reduced final number of leaves (developmental scale). However in the phyA cry1 cry2 triple mutant background the phyB mutation accelerates flowering on a developmental scale but severely delays flowering on a time scale. The long photoperiods inducing flowering are perceived by the leaves. Flowering signals that could include hormones and sugars migrate from the leaves to the apex in response to the light stimulus. We propose to compare the following mRNA samples of expanding leaves: 1) wild type 2) phyB mutant 3) phyA cry1 cry2 triple mutant 4) phyA phyB cry1 cry2 quadruple mutant. The comparison between the wild type and the phyB mutant will help to uncover the changes in leaf mRNA patterns underlying enhanced petiole growthreduced pigmentation and early flowering in response to the absence of phyB activity. The comparison between the phyA cry1 cry2 triple mutant and the phyA phyB cry1 cry2 quadruple mutant should reveal the mRNA differences between photosynthetic leaves with dramatically different abilities to expand. The added value of the simultaneous analysis of the two comparisons is that effect of phyB is different in both genetic backgrounds and this should provide information on the mechanisms and significance of photoreceptor interactions.

Project description:The far-red light (FR) photoreceptor phytochrome A (phyA) contains no DNA binding domain but associates with CHS promoter through its chaperon FHY1 and transcription factors to regulate transcription. Here, we performed a genome-wide identification of phyA targets using a combination of phyA ChIP- and RNA-sequencing methods. Our results indicate that the phyA signaling widely impact gene promoters involved in multiple FR-modulated aspects of plant growth. Furthermore, there was an enrichment of hormones- and stresses-responsive elements in the phyA direct target promoters, indicating that a much broader than expected range of transcription factors are involved in the phyA signaling. To verify our hypothesis that phyA regulates genes other than light-responsive ones through interaction with corresponding transcription factors, we examined the phyA action on one of its direct target gene NAC019, encoding an ABAdependent transcription factor. The phyA signaling cascade, consisting of FHY1 and HY5, not only targets two G-boxes on NAC019 promoter for subsequent transcriptional regulation, but also positively coordinates with ABA response for the root elongation inhibition under FR. Our study provides new insights into how plants rapidly fine-tune their growth strategy upon dynamic light environment by escorting photoreceptors to the promoters of hormones- or stresses-responsive genes for individualized modulation. Four day-old PphyA: phyA-GFP phyA201 transgenic seedlings were irradiated with 3h FR for ChIP with an anti-GFP antibody, which was previously used to detect phyA-GFP upon FR irradiation . Three biologically distinct phyA associated-DNA samples were subjected to library construction and high-throughput Solexa (Illumina) sequencing. An input DNA sample (genomic DNA before antibody immunoprecipitation in ChIP) was sequenced in parallel to exclude false positive signals caused by preferential PCR on certain genomic regions in the process of library construction .

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Antagonistic action of PHYA and PHYB is involved in FR-dependent leaf senescence in Arabidopsis accessions

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