宏观的相互作用
At least nine groups of plant hormones have been studied extensively. Auxin, cytokinin, brassinosteroid (BR), gibberellin (GA), and strigolactone (SL) play essential roles in normal growth and development.
example1 :Integration of Light and Hormone Signaling Pathways Regulates Hypocotyl Elongation
暗形态建成表型 skotomorphogenesis / etiolation
- maximum hypocotyl elongation,
- limited root growth
- closed cotyledons with an apical hook
- suppression of chloroplast development
光照后转变为光形态建成 photomorphogenesis / de-etiolation
- inhibition of hypocotyl elongation
- opening/expanding and greening of cotyledonsand leaves
- acceleration of root growth****
The phytochrome interacting factors (PIFs), a class of basic helix-loop-helix (bHLH) factors, are major posi- tive regulators of shoot cell elongation.
Elongated hypocotyl5 (HY5),GATA2/4, and B-box factors including BZS1 are negative reg-ulators of cell elongation, and they are degraded in the dark
through the E3 ubiquitin ligase constitutive photomorphogenic1(COP1), which is inactivated by both phytochromes and crypto-chromes。
GA, similar to auxin, acts through an intracellular receptor to promote ubiquitination and degradation of key repressor proteins, named DELLA proteins for containing a conserved Asp-Glu-Leu-Leu-Ala amino acid sequence。
DELLAs were initially found to interact with PIFs and inhibit their DNA-binding activity but have since been found to inhibit DNA-binding activities of many transcription factors, including BZR1 and ARF6 of the BR and auxin pathways, respectively. DELLAs also function as transcriptional co-activators through interaction with several classes of DNA-binding proteins, including ARR1, which is a component of the cytokinin pathway that promotes photomorphogenesis.
the BR, auxin, GA, and phyto- chrome pathways converge through direct interactions among their transcription factors/regulators. BZR1, PIF4, and ARF6 interact with each other, and they share a large number of com- mon target genes.These three transcription factors enhance each other’s target binding and transcriptional activation activities, and their functions in acti- vating many shared target genes and promoting hypocotyl elongation are genetically interdependent on each other.
(A) Light and hormonal signals (red text) are perceived by cell-surface or intracellular receptors (blue), which regulate transcription factors (green) through signaling/posttranslational mechanisms (red lines), whereas the transcription factors transcriptionally regulate (blue lines) downstream responses and components of other pathways. Orange: kinases; yellow: phosphatases;** purple: inhibitors of transcription factors.**
(B) Transcriptional integration by the BAP/D-HHbH circuit. Red and blue lines show regulation at the protein and RNA (transcriptional) levels, respectively.
example2: The Tradeoffs between Growth and Defense
BR and the flagellin-signaling pathways
A peptide (flg22) from bacterial flagellin protein is perceived as a pathogen-asso- ciated molecular pattern (PAMP) by the LRR-RK named FLS2 (flagellin-sensitive2), which has an overall similar structure as the BR receptor BRI1.
Flg22 induces microRNA miR393, which targets the mRNAs of auxin receptor TIR1, AFB2, and AFB3.
Wounding by herbivores induces production of JA, which acts as a mobile signal to induce systemic defense responses and inhibit vegetative growth
A) Mechanisms of crosstalks of FLS2-mediated flagellin signaling with the BR and auxin pathways.
(B) Growth regulation in response to herbivore attack, mediated by crosstalk between the GA and JA pathways. Red and blue lines show regulation at the protein and RNA (transcriptional) levels, respectively. Dashed lines indicate unknown mechanisms.
example3 :Shade Avoidance Syndrome: A Case of Inter-organ Growth Coordination
In nature, successful competition with neighbors for sunlight is crucial for plant survival, and thus canopy shade induces a vari- ety of morphological changes that are collectively called** shade avoidance syndrome (SAS)**. These include elongation of stem and petiole, leaf hyponasty (upward bending of the leaves caused by growth of the lower side), reduced shoot branching and root growth, and decreased seed and fruit production.
(A) Diagram of light-hormone interactions in growth regulation under full light (left) and shade (right) conditions. HBL: high blue light, LBL: low blue light, HRFR: high red:far-red ratio, LRFR: low red:far-red ratio. Dark text and arrows show active components and their activities, and dimmed text and arrows indicated inactivated components and activities. Red arrows show the flow of auxin.
(B and C) Venn diagram shows overlaps between genes induced by 1 hr low R:FR treatment, or by 6 hr low blue light treatment of light-grown seedlings, and the target genes of BZR1, PIF4, and ARF6 identified by ChIP-seq in dark-grown seedlings.
http://dx.doi.org/10.1016/j.cell.2016.01.044
微观的细胞间相互联系
Communication between cells is a crucial step to coordinate organ formation and tissue patterning. In plants, the intercellular transport of metabolites and signalling molecules occur symplastically through membranous structures (named plasmodesmata) that traverse the cell wall to connect the cytoplasm and endoplasmic reticulum of neighbouring cells.
- Plasmodesmata (PD) play a role in organ development and patterning.
- Proteins that localize and/or interact to regulate PD have been identified.
- Novel mobile transcription factors and RNAs support PD role in organ formation.
Plasmodesmata regulation during organ formation and vascular patterning
plant cells communicate to each other and form higher order structures that characterize organisms – plasmodesmata (PD) 胞间连丝
In simple terms, PD are channels made of plasma mem- brane (PM) that provide cytoplasmic and membranous continuity between neighbouring cells forming the symplasm
Transport pathways and PD regulation by callose.
(a) Intercellular transport occur through PD cytoplasmic sleeve (black arrows), by diffusion in the lumen of the endoplasmic reticulum (ER) and the desmotubule (DT) (orange arrows) and, potentially, by lateral segregation in the membranes (green discontinuous arrows). Plasma membrane (PM), cell wall (CW) and PD-cytoplasmic aperture (in discontinuous blue) are indicated.
(b) PD transport is regulated by the deposition of callose in the surrounding cell wall. Callose 胼胝质 is produced at PD sites from UDP-glucose by callose synthases (CALS) and degraded to glucose subunits by PD-located beta-1,3 glucanases (PdBG). Callose turnover depends on the activity of these enzymes. High levels of callose restricts PD-cytoplasmic aperture blocking molecular transport thus cell-to-cell symplastic connectivity.
Receptor proteins act at plasmodesmata to regulate organ development
Analysis of the PD proteome in Arabi- dopsis identified three receptor-like kinases (RLKs) and a number of receptor-like proteins including the PD-Lo- cated Proteins (PDLPs).
Although most of the research in PD-located receptor proteins focuses on their function in plant–pathogen interactions, new cumulative data support their role in development.
Interaction of receptor proteins is also proposed as a mechanism to regulate the PD transport of factors main- taining stem cell fate in the apical meristems
Identification and developmental function of novel mobile proteins and RNAs
List of mobile proteins (blue shaded cells) and small RNAs (in green) studied in the last five years with a function in organ development and patterning.
The importance of mobile RNA molecules in tissue patterning and organ development emerged from recent publications.
Thousands of transcripts moving in the phloem of Arabidopsis and other plant species were identified using different strategies (such as grafting, translocation of RNA between host and parasitic plants and phloem sap analysis). These phloem RNA molecules move long-distances and between CC and SE, by diffusion or in complex with RNA-binding proteins, to regulate development in target tissues. However questions remain regarding the selectivity for phloem translocation or the final destination of these transcripts.
The transport of miRNA and siRNA molecules can also be phloem independent. Research on miR394 suggests that it moves from the L1 layer of the SAM to the inner stem cell layers to repress LEAF CURLING RESPONSIVENESS (LCR, a gene involved in leaf and shoot meristem development) acting as a positional cue to maintain shoot stem cell activity. Also important for patterning, miR165/166 move between cell layers in embryos and root meristem to regulate CLASS III HOMEODOMAIN LEUCINE ZIPPER (HD-ZIP III) proteins.
In turn, tasiR-ARF, a trans-acting siRNA that targets AUXIN RESPONSE FACTOR 3 (ARF3) and ARF4, diffuses from the adaxial to the abaxial side to establish leaf polarity. siRNA can also move long-distances in a phloem-independent pathway from root to shoot [67]. When produced in roots, siRNA moves to the shoot by a combination of short-range cell-to-cell communication events and amplification of the signal in all cells en route. Interestingly, the spreading of the silencing signal is affected in mutants in a hydrogen peroxide (H2O2)-producing type III peroxidase (named RCI3) concordant with previous research indicating the role of H2O2 on regulating PD permeability.
Together, the findings support the involvement of PD in the transport of siRNA and their role in developmental signalling.
文献
- M. Notaguchi Identification of phloem-mobile mRNA J Plant Res, 128 (2015), pp. 27–35
- C. Zhang, L. Han, T.L. Slewinski, J. Sun, J. Zhang, Z.Y. Wang, R. Turgeon Symplastic phloem loading in poplar Plant Physiol, 166 (2014), pp. 306–313
- Z. Spiegelman, G. Golan, S. Wolf Don’t kill the messenger: long-distance trafficking of mRNA molecules Plant Sci, 213 (2013), pp. 1–8
- D.J. Hannapel, P. Sharma, T. Lin Phloem-mobile messenger RNAs and root development Front Plant Sci, 4 (2013), p. 257
- B.K. Ham, G. Li, W. Jia, J.A. Leary, W.J. Lucas Systemic delivery of siRNA in pumpkin by a plant PHLOEM SMALL RNA-BINDING PROTEIN 1-ribonucleoprotein complex Plant J, 80 (2014), pp. 683–694
http://dx.doi.org/10.1016/j.pbi.2015.10.007
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