Genes controlling plant growth and form are of considerable interest, because they affect survival and productivity traits, and are largely unknown or poorly characterized. The SHORT INTERNODES (SHI) ...gene is one of a 10-member SHI-RELATED SEQUENCE (SRS) gene family in Arabidopsis that includes important developmental regulators. Using comparative sequence analysis of the SRS gene families in poplar and Arabidopsis, we identified two poplar proteins that are most similar to SHI and its closely related gene STYLISH1 (STY1). The two poplar genes are very similar in sequence and expression and are therefore probably paralogs with redundant functions. RNAi suppression of the two Populus genes enhanced shoot and root growth, whereas the overexpression of Arabidopsis SHI in poplar reduced internode and petiole length. The suppression of the two genes increased fiber length and the proportion of xylem tissue, mainly through increased xylem cell proliferation. The transgenic modifications were also associated with significant changes in the concentrations of gibberellins and cytokinin. We conclude that Populus SHI-RELATED SEQUENCE (SRS) genes play an important role in the regulation of vegetative growth, including wood formation, and thus could be useful tools for the modification of biomass productivity, wood quality or plant form.
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Selenite is a predominant form of selenium (Se) available to plants, especially in anaerobic soils, but the molecular mechanism of selenite uptake by plants is not well understood.
ltn1, a rice ...mutant previously shown to have increased phosphate (Pi) uptake, was found to exhibit higher selenite uptake than the wild-type in both concentration- and time-dependent selenite uptake assays. Respiratory inhibitors significantly inhibited selenite uptake in the wildtype and the ltn1 mutant, indicating that selenite uptake was coupled with H+ and energydependent. Selenite uptake was greatly enhanced under Pi-starvation conditions, suggesting that Pi transporters are involved in selenite uptake.
OsPT2, the most abundantly expressed Pi transporter in the roots, is also significantly upregulated in ltn1 and dramatically induced by Pi starvation. OsPT2-overexpressing and knockdown plants displayed significantly increased and decreased rates of selenite uptake, respectively, suggesting that OsPT2 plays a crucial role in selenite uptake. Se content in rice grains also increased significantly in OsPT2-overexpressing plants.
These data strongly demonstrate that selenite and Pi share similar uptake mechanisms and that OsPT2 is involved in selenite uptake, which provides a potential strategy for breeding Seenriched rice varieties.
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AP2/ERF-type transcription factors regulate important functions of plant growth and development as well as responses to environmental stimuli. A rice AP2/ERF transcription factor, OsEREBP1 is a ...downstream component of a signal transduction pathway in a specific interaction between rice (Oryza sativa) and its bacterial pathogen, Xoo (Xanthomonas oryzae pv. oryzae). Constitutive expression of OsEREBP1 in rice driven by maize ubiquitin promoter did not affect normal plant growth. Microarray analysis revealed that over expression of OsEREBP1 caused increased expression of lipid metabolism related genes such as lipase and chloroplastic lipoxygenase as well as several genes related to jasmonate and abscisic acid biosynthesis. PR genes, transcription regulators and Aldhs (alcohol dehydrogenases) implicated in abiotic stress and submergence tolerance were also upregulated in transgenic plants. Transgenic plants showed increase in endogenous levels of α-linolenate, several jasmonate derivatives and abscisic acid but not salicylic acid. Soluble modified GFP (SmGFP)-tagged OsEREBP1 was localized to plastid nucleoids. Comparative analysis of non-transgenic and OsEREBP1 overexpressing genotypes revealed that OsEREBP1 attenuates disease caused by Xoo and confers drought and submergence tolerance in transgenic rice. Our results suggest that constitutive expression of OsEREBP1 activates the jasmonate and abscisic acid signalling pathways thereby priming the rice plants for enhanced survival under abiotic or biotic stress conditions. OsEREBP1 is thus, a good candidate gene for engineering plants for multiple stress tolerance.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Steroidal alkaloids (SAs) are triterpene-derived specialized metabolites found in members of the Solanaceae family that provide plants with a chemical barrier against a broad range of pathogens. ...Their biosynthesis involves the action of glycosyltransferases to form steroidal glycoalkaloids (SGAs). To elucidate the metabolism of SGAs in the Solanaceae family, we examined the tomato (Solanum lycopersicum) GLYCOALKALOID METABOLISM1 (GAME1) gene. Our findings imply that GAME1 is a galactosyltransferase, largely performing glycosylation of the aglycone tomatidine, resulting in SGA production in green tissues. Downregulation of GAME1 resulted in an almost 50% reduction in α-tomatine levels (the major SGA in tomato) and a large increase in its precursors (i.e., tomatidenol and tomatidine). Surprisingly, GAME1-silenced plants displayed growth retardation and severe morphological phenotypes that we suggest occur as a result of altered membrane sterol levels caused by the accumulation of the aglycone tomatidine. Together, these findings highlight the role of GAME1 in the glycosylation of SAs and in reducing the toxicity of SA metabolites to the plant cell.
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Increased cellular ploidy is widespread during developmental processes of multicellular organisms, especially in plants. Elevated ploidy levels are typically achieved either by endoreplication or ...endomitosis, which are often regarded as modified cell cycles that lack an M phase either entirely or partially. We identified GIGAS CELL1 (GIG1)/OMISSION OF SECOND DIVISION1 (OSD1) and established that mutation of this gene triggered ectopic endomitosis. On the other hand, it has been reported that a paralog of GIG1/OSD1, UV-INSENSITIVE4 (UVI4), negatively regulates endoreplication onset in Arabidopsis thaliana. We showed that GIG1/OSD1 and UVI4 encode novel plant-specific inhibitors of the anaphase-promoting complex/cyclosome (APC/C) ubiquitin ligase. These proteins physically interact with APC/C activators, CDC20/FZY and CDH1/FZR, in yeast two-hybrid assays. Overexpression of CDC20.1 and CCS52B/FZR3 differentially promoted ectopic endomitosis in gig1/osd1 and premature occurrence of endoreplication in uvl4. Our data suggest that GIG1/OSD1 and UVI4 may prevent an unscheduled increase in cellular ploidy by preferentially inhibiting APC/C CDC ²⁰ and APC/C FZR , respectively. Generation of cells with a mixed identity in gig1/osd1 further suggested that the APC/C may have an unexpected role for cell fate determination in addition to its role for proper mitotic progression.
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Summary
Cytokinin is known to have negative effects on de novo auxin‐induced root formation. However, the regulatory mechanisms of root initiation by both cytokinin and auxin are poorly understood. ...In this study, we characterized a rice mutant, termed crown rootless5 (crl5), which produced fewer crown roots and displayed impaired initiation of crown root primordia. The expression of CRL5, which encodes a member of the large AP2/ERF transcription factor family protein, was observed in the stem region where crown root initiation occurs. Exogenous auxin treatment induced CRL5 expression without de novo protein biosynthesis, which also required the degradation of AUX/IAA proteins. A putative auxin response element in the CRL5 promoter region specifically interacted with a rice ARF, demonstrating that CRL5 may be a direct target of an ARF, similar to CRL1/ADVENTITIOUS ROOTLESS1 (ARL1) that also regulates crown root initiation. A crl1 crl5 double mutant displayed an additive phenotype, indicating that these two genes function in different genetic pathways for crown root initiation. In addition, ProACT:CRL5/WT showed a cytokinin‐resistant phenotype for crown root initiation, and also up‐regulated the expression of two negative regulators of cytokinin signaling, OsRR1 and OsRR2, which were downregulated in crl5. Transgenic plants that over‐expressed OsRR1 under the control of the CRL5 promoter in a crl5 mutant background produced a higher number of crown roots than the crl5 plant. Taken together, these results indicate that auxin‐induced CRL5 promotes crown root initiation through repression of cytokinin signaling by positively regulating type‐A RR, OsRR1.
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Abscisic acid (ABA) is a phytohormone that positively regulates seed dormancy and stress tolerance. PYL/RCARs were identified an intracellular ABA receptors regulating ABA-dependent gene expression ...inArabidopsis thaliana. However, their function in monocot species has not been characterized yet. Herein, it is demonstrated that PYL/RCAR orthologues inOryza sativafunction as a positive regulator of the ABA signal transduction pathway. Transgenic rice plants expressing OsPYL/RCAR5, a PYL/RCAR orthologue of rice, were found to be hypersensitive to ABA during seed germination and early seedling growth. A rice ABA signalling unit composed of OsPYL/RCAR5, OsPP2C30, SAPK2, and OREB1 for ABA-dependent gene regulation was further identified, via interaction assays and a transient gene expression assay. Thus, a core signalling unit for ABA-responsive gene expression modulating seed germination and early seedling growth in rice has been unravelled. This study provides substantial contributions toward understanding the ABA signal transduction pathway in rice.
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Limonium bicolor
, a typical recretohalophyte that lives in saline environments, excretes excessive salt to the environment through epidermal salt glands to avoid salt stress. The aim of this study ...was to screen for
L. bicolor
genes involved in salt secretion by high-throughput RNA sequencing. We established the experimental procedure of salt secretion using detached mature leaves, in which the optimal salt concentration was determined as 200 mM NaCl. The detached salt secretion system combined with Illumina deep sequencing were applied. In total, 27,311 genes were annotated using an
L. bicolor
database, and 2040 of these genes were differentially expressed, of which 744 were up-regulated and 1260 were down-regulated with the NaCl versus the control treatment. A gene ontology enrichment analysis indicated that genes related to ion transport, vesicles, reactive oxygen species scavenging, the abscisic acid-dependent signaling pathway and transcription factors were found to be highly expressed under NaCl treatment. We found that 102 of these genes were likely to be involved in salt secretion, which was confirmed using salt-secretion mutants. The present study identifies the candidate genes in the
L. bicolor
salt gland that are highly associated with salt secretion. In addition, a salt-transporting pathway is presented to explain how Na
+
is excreted by the salt gland in
L. bicolor
. These findings will shed light on the molecular mechanism of salt secretion from the salt glands of plants.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
30.
SCFTIR1/AFB-Based Auxin Perception Salehin, Mohammad; Bagchi, Rammyani; Estelle, Mark
The Plant cell,
01/2015, Volume:
27, Issue:
1
Journal Article
Peer reviewed
Open access
Auxin regulates a vast array of growth and developmental processes throughout the life cycle of plants. Auxin responses are highly context dependent and can involve changes in cell division, cell ...expansion, and cell fate. The complexity of the auxin response is illustrated by the recent finding that the auxin-responsive gene set differs significantly between different cell types in the root. Auxin regulation of transcription involves a core pathway consisting of the TIR1/AFB F-box proteins, the Aux/IAA transcriptional repressors, and the ARF transcription factors. Auxin is perceived by a transient coreceptor complex consisting of a TIR1/AFB protein and an Aux/IAA protein. Auxin binding to the coreceptor results in degradation of the Aux/IAAs and derepression of ARF-based transcription. Although the basic outlines of this pathway are now well established, it remains unclear how specificity of the pathway is conferred. However, recent results, focusing on the ways that these three families of proteins interact, are starting to provide important clues.
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