Floral transition initiates reproductive development of plants and occurs in response to environmental and endogenous signals. In Arabidopsis thaliana, this process is accelerated by several ...environmental cues, including exposure to long days. The photoperiod-dependent promotion of flowering involves the transcriptional induction of FLOWERING LOCUS T (FT) in the phloem of the leaf. FT encodes a mobile protein that is transported from the leaves to the shoot apical meristem, where it forms part of a regulatory complex that induces flowering. Whether FT also has biological functions in leaves of wild-type plants remains unclear.
In order to address this issue, we first studied the leaf transcriptomic changes associated with FT overexpression in the companion cells of the phloem. We found that FT induces the transcription of SWEET10, which encodes a bidirectional sucrose transporter, specifically in the leaf veins. Moreover, SWEET10 is transcriptionally activated by long photoperiods, and this activation depends on FT and one of its earliest target genes SUPPRESSOR OF CONSTANS OVEREXPRESSION 1 (SOC1). The ectopic expression of SWEET10 causes early flowering and leads to higher levels of transcription of flowering-time related genes in the shoot apex.
Collectively, our results suggest that the FT-signaling pathway activates the transcription of a sucrose uptake/efflux carrier during floral transition, indicating that it alters the metabolism of flowering plants as well as reprogramming the transcription of floral regulators in the shoot meristem.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Serine/arginine-rich (SR) proteins are major modulators of alternative splicing, a key generator of proteomic diversity and flexible means of regulating gene expression likely to be crucial in plant ...environmental responses. Indeed, mounting evidence implicates splicing factors in signal transduction of the abscisic acid (ABA) phytohormone, which plays pivotal roles in the response to various abiotic stresses. Using real-time RT-qPCR, we analyzed total steady-state transcript levels of the 18 SR and two SR-like genes from Arabidopsis thaliana in seedlings treated with ABA and in genetic backgrounds with altered expression of the ABA-biosynthesis ABA2 and the ABA-signaling ABI1 and ABI4 genes. We also searched for ABA-responsive cis elements in the upstream regions of the 20 genes. We found that members of the plant-specific SC35-Like (SCL) Arabidopsis SR protein subfamily are distinctively responsive to exogenous ABA, while the expression of seven SR and SR-related genes is affected by alterations in key components of the ABA pathway. Finally, despite pervasiveness of established ABA-responsive promoter elements in Arabidopsis SR and SR-like genes, their expression is likely governed by additional, yet unidentified cis-acting elements. Overall, this study pinpoints SR34, SR34b, SCL30a, SCL28, SCL33, RS40, SR45 and SR45a as promising candidates for involvement in ABA-mediated stress responses.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Five dinuclear copper(
i
) complexes of the type Cu{κ
N
,κ
N
′-5-R-NC
4
H
2
-2-C(H)&z.dbd;N(2,6-iPr
2
C
6
H
3
)}
2
(
1a-e
; R = 2,4,6-iPr
3
C
6
H
2
(
a
), R = 2,6-Me
2
C
6
H
3
(
b
), R = 3,5-(CF
3
)
...2
C
6
H
3
(
c
), R = 2,6-(OMe)
2
C
6
H
2
(
d
), R = CPh
3
(
e
)) were prepared by the reaction of the respective 5-R-2-iminopyrrolyl potassium salts
KLa-e
and Cu(NCMe)
4
BF
4
in moderate yields. These new copper(
i
) complexes were characterized by NMR spectroscopy, elemental analysis and, in selected cases, by single crystal X-ray diffraction and their structural and electronic features further analyzed by DFT calculations and cyclic voltammetry, respectively. X-ray diffraction studies reveal dimeric Cu structures assembled by 2-iminopyrrolyl bridging ligands adopting a transoid conformation (complexes
1a
and
1d
), while complexes
1c
and
1e
displayed a cisoid conformation of those moieties, with respect to the Cu(
i
) centers. Additionally, VT-
1
H NMR and
1
H-
1
H NOESY NMR experiments on complexes
1a-e
exhibited complex fluxional processes in solution, assigned to a conformational inversion of the respective Cu
2
N
4
C
4
metallacycles in all complexes but
1c
, accompanied by a cisoid-transoid isomerization in the cases of complexes
1d,e
. The Cu(
i
) complexes were also analyzed by cyclic voltammetry, where all complexes exhibit two oxidation processes, where the first oxidation is reversible, with the exception of
1b
and
1c
, which also show the highest oxidation potentials. The oxidation potentials follow clear trends related to the structural parameters of the complexes, in particular the Cu Cu distance and the Cu
2
N
4
C
4
macrocycles torsion angles. All new 5-substituted-2-iminopyrrolyl Cu(
i
) complexes
1a-e
served as catalysts for azide-alkyne cycloaddition (CuAAC) reactions, being able to generate the respective 1,2,3-triazole products in yields as high as 82% and turnover frequencies (TOFs) as high as 859 h
−1
, after optimizing the conditions. The activity, as measured by the TOF, is in accordance with the oxidation potential of the corresponding complexes, the easier the oxidation, the higher the TOF value. Complex
1-H
, where R = H, proved to be a poor catalyst for the same reactions, indicating that the 5-substitution in the ligand framework is crucial in stabilizing any potential catalytic species.
New well-defined dinuclear copper(
i
) complexes of bulky 5-substituted-2-iminopyrrolyl ligands were synthesised and characterized, displaying high activity in catalytic azide-alkyne cycloadditions.
Plant cells can change their identity based on positional information, a mechanism that confers developmental plasticity to plants. This ability, common to distinct multicellular organisms, is ...particularly relevant for plant phloem cells. Protophloem sieve elements (PSEs), one type of phloem conductive cells, act as the main organizers of the phloem pole, which comprises four distinct cell files organized in a conserved pattern. Here, we report how Arabidopsis roots generate a reservoir of meristematic phloem cells competent to swap their cell identities. Although PSE misspecification induces cell identity hybridism, the activity of RECEPTOR LIKE PROTEIN KINASE 2 (RPK2) by perceiving CLE45 peptide contributes to restrict PSE identity to the PSE position. By maintaining a spatiotemporal window when PSE and PSE-adjacent cells’ identities are interchangeable, CLE45 signaling endows phloem cells with the competence to re-pattern a functional phloem pole when protophloem fails to form.
Display omitted
•An early PSE misspecification promotes identity hybridism between PSE and CC•Meristematic CC and MSE retain plastic identity to safeguard phloem functionality•RPK2 excludes PSE identity from PSE-surrounding cells within the root meristem•CLE45 maintains PSE and PSE-surrounding cells in a plastic identity stage
Gujas et al. describe a molecular mechanism that endows plant cells with a plastic cell fate. Hereby, CLE-RPK2 module halts heterogeneous phloem cells sub-specification. This plastic identity state safeguards the re-establishment of a functional phloem pattern in case conductive protophloem fails to form in its by-lineage-predestined position.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPUK, ZAGLJ, ZRSKP
The plant vascular network consists of specialized phloem and xylem elements that undergo two distinct morphogenetic developmental programs to become transport-functional units. Whereas vacuolar ...rupture is a determinant step in protoxylem differentiation, protophloem elements never form a big central vacuole. Here, we show that a genetic disturbance of phosphatidylinositol 4,5-bis-phosphate PtdIns(4,5)P
homeostasis rewires cell trafficking towards the vacuole in
roots. Consequently, an enhanced phosphoinositide-mediated vacuolar biogenesis correlates with premature programmed cell death (PCD) and secondary cell wall elaboration in xylem cells. By contrast, vacuolar fusion events in protophloem cells trigger the abnormal formation of big vacuoles, preventing cell clearance and tissue functionality. Removal of the inositol 5' phosphatase COTYLEDON VASCULAR PATTERN 2 from the plasma membrane (PM) by brefeldin A (BFA) treatment increases PtdIns(4,5)P
content at the PM and disrupts protophloem continuity. Conversely, BFA application abolishes vacuolar fusion events in xylem tissue without preventing PCD, suggesting the existence of additional PtdIns(4,5)P
-dependent cell death mechanisms. Overall, our data indicate that tight PM phosphoinositide homeostasis is required to modulate intracellular trafficking contributing to oppositely regulate vascular differentiation.
Summary
Efficient root‐to‐shoot delivery of water and nutrients in plants relies on the correct differentiation of xylem cells into hollow elements. While auxin is integral to the formation of xylem ...cells, it remains poorly characterized how each subcellular pool of this hormone regulates this process.
Combining genetic and cell biological approaches, we investigated the bipartite activity of nucleoplasmic vs plasma membrane‐associated phosphatidylinositol 4‐phosphate kinases PIP5K1 and its homolog PIP5K2 in Arabidopsis thaliana roots and uncovered a novel mechanism by which phosphoinositides integrate distinct aspects of the auxin signaling cascade and, in turn, regulate the onset of xylem differentiation.
The appearance of undifferentiated cells in protoxylem strands of pip5k1 pip5k2 is phenomimicked in auxin transport and perception mutants and can be partially restored by the nuclear residence of PIP5K1. By contrast, exclusion of PIP5K1 from the nucleus hinders the auxin‐mediated induction of the xylem master regulator VASCULAR RELATED NAC DOMAIN (VND) 7. A xylem‐specific increase of auxin levels abolishes pip5k1 pip5k2 vascular defects, indicating that the establishment of auxin maxima is required to activate VND7‐mediated xylem differentiation.
Our results describe a new mechanism by which distinct subcellular pools of phosphoinositides integrate auxin transport and perception to initiate xylem differentiation in a spatiotemporal manner.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
SR proteins are conserved RNA‐binding proteins best known as splicing regulators that have also been implicated in other steps of gene expression. Despite mounting evidence for a role in plant ...development and stress responses, the molecular pathways underlying SR protein regulation of these processes remain poorly understood. Here we show that the plant‐specific SCL30a SR protein negatively regulates ABA signaling to control seed traits and stress responses during germination in Arabidopsis. Transcriptome‐wide analyses revealed that loss of SCL30a function barely affects splicing, but largely induces ABA‐responsive gene expression and genes repressed during germination. Accordingly, scl30a mutant seeds display delayed germination and hypersensitivity to ABA and high salinity, while transgenic plants overexpressing SCL30a exhibit reduced ABA and salt stress sensitivity. An ABA biosynthesis inhibitor rescues the enhanced mutant seed stress sensitivity, and epistatic analyses confirm that this hypersensitivity requires a functional ABA pathway. Finally, seed ABA levels are unchanged by altered SCL30a expression, indicating that the gene promotes seed germination under stress by reducing sensitivity to the phytohormone. Our results reveal a new player in ABA‐mediated control of early development and stress response.
Summary statement
We found that an Arabidopsis SR protein represses ABA‐induced gene expression to modulate seed traits and germination. Our results uncover a new player in ABA‐mediated control of early plant development and stress responses.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Magnetic reconnection is thought to drive a wide variety of dynamic phenomena in the solar atmosphere. Yet, the detailed physical mechanisms driving reconnection are difficult to discern in the ...remote sensing observations that are used to study the solar atmosphere. In this Letter, we exploit the high-resolution instruments Interface Region Imaging Spectrograph and the new CHROMIS Fabry-Pérot instrument at the Swedish 1-m Solar Telescope (SST) to identify the intermittency of magnetic reconnection and its association with the formation of plasmoids in so-called UV bursts in the low solar atmosphere. The Si iv 1403 UV burst spectra from the transition region show evidence of highly broadened line profiles with often non-Gaussian and triangular shapes, in addition to signatures of bidirectional flows. Such profiles had previously been linked, in idealized numerical simulations, to magnetic reconnection driven by the plasmoid instability. Simultaneous CHROMIS images in the chromospheric Ca ii K 3934 line now provide compelling evidence for the presence of plasmoids by revealing highly dynamic and rapidly moving brightenings that are smaller than 0 2 and that evolve on timescales of the order of seconds. Our interpretation of the observations is supported by detailed comparisons with synthetic observables from advanced numerical simulations of magnetic reconnection and associated plasmoids in the chromosphere. Our results highlight how subarcsecond imaging spectroscopy sensitive to a wide range of temperatures combined with advanced numerical simulations that are realistic enough to compare with observations can directly reveal the small-scale physical processes that drive the wide range of phenomena in the solar atmosphere.
The role of 2‐iminopyrrolyl copper(I) complexes in the Reversible‐Deactivation Radical Polymerization (RDRP) of methyl methacrylate (MMA) is described. Mononuclear 2‐iminopyrrolyl copper(I) complexes ...Cu{κ2N,N′‐NC4H3‐2‐C(H)=NR′}Ln 1–7 (R′ = C6H5, Ln = (PPh3)2 (1); R′ = 2,6‐Me2C6H3, Ln = (PPh3)2 (2); R′ = 2,6‐iPr2C6H3, Ln = (PPh3)2 (3); R′ = 4‐NMe2C6H4, Ln = (PPh3)2 (4); R′ = CH3, Ln = (PPh3)2 (5); R′ = CH3, Ln = (PMe3)2 (6); R′ = CH3, Ln = PiPr3 (7)) were synthesized by the reaction of the in situ prepared sodium salts of precursors HL1–5 with Cu(NCMe)4BF4 with the respective phosphines. In their absence, the binuclear complex Cu{κN,κN'‐NC4H3‐2‐C(H)=NCH3}2 8 was formed instead, which, when treated with one equivalent of PR3 yielded the binuclear complexes Cu2{κN,κN'‐NC4H3‐2‐C(H)=NCH3}2PR3 9 (R = Ph) and 10 (R = Me).
All complexes, except 8, were active in the RDRP of MMA using the initiator tert‐butyl‐α‐bromoisobutyrate (tBiB‐Br), achieving apparent propagation kinetic constants (kp') in the range of 0.5–7.5 × 10−5 s−1, at 90 °C and with a MMA0:complex0:tBiB‐Br0 ratio of 500:1:1. All reactions yielded poly (methyl methacrylate)s with molecular weights (
M¯n) and dispersities higher than expected for Controlled Radical Polymerization processes. Complex 7 achieved the best results, with
M¯n values being only 1.2‐fold higher than theoretically expected. Experimental and density functional theory (DFT) studies suggest that this system operates via Atom Transfer Radical Polymerization/Organometallic Mediated Radical Polymerization (ATRP/OMRP) mechanisms interplay.
A family of mononuclear and binuclear 2‐iminopyrrolyl copper(I) complexes with phosphine ligands were synthesized and characterized. The new complexes mediated the Reversible‐Deactivation Radical Polymerization of methyl methacrylate.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
The combination of Co (II) {κ 2 N,O-NC 4 H 3 -C(H)O} 2 (PMe 3 ) 2 ( 1 ) and tert -butyl-α-bromoisobutyrate ( t BiB-Br) is a suitable initiation system for controlling the radical polymerization of ...styrene, by an atom transfer radical polymerization (ATRP) mechanism, below 70 °C and of methyl methacrylate, by an organometallic mediated radical polymerization (OMRP)/catalytic chain transfer (CCT) interplay mechanism, below 50 °C. The pure ATRP nature of styrene polymerization allowed the synthesis of the polystyrene- b -poly(methyl methacrylate) block copolymer, as confirmed by GPC/SEC and DOSY NMR studies. Attempts to isolate a Co( iii ) species containing a Br atom ( Co(iii)–Br ), supposedly a key ATRP deactivator, by reacting 1 and t BiB-Br quantitatively afforded the cationic Co( iii ) complex Co (III) {κ 2 N,O-NC 4 H 3 -C(H)O} 2 (PMe 3 ) 2 Br ( 2 ). Metathetic exchange reactions of complex 2 with TlX gave rise to analogues of the type Co (III) {κ 2 N,O-NC 4 H 3 -C(H)O} 2 (PMe 3 ) 2 X ( 3a , X = BF 4 − ; 3b , X = BPh 4 − ), containing non-coordinating anions. In the absence of a radical initiator, complex 2 mediated the formation of polystyrene and poly(methyl methacrylate), with poor control, likely via a generation of activators by a monomer addition (GAMA) mechanism. Complexes 3a and 3b , however, have been shown to be completely inactive. Addition of 0.5 equivalents of AIBN to 2 drastically improved the molecular weight control in the polymerization of styrene, at 70 °C, through a reverse-ATRP mechanism.
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