Summary
UV‐B radiation inhibits plant growth, and this inhibition is, to a certain extent, regulated by miR396‐mediated repression of Growth Regulating Transcription factors (GRFs). Moreover, E2Fe ...transcription factor also modulates Arabidopsis leaf growth. Here, we provide evidence that, at UV‐B intensities that induce DNA damage, E2Fc participates in the inhibition of cell proliferation. We demonstrate that E2Fc‐deficient plants show a lower inhibition of leaf size under UV‐B conditions that damage DNA, decreased cell death after exposure and altered SOG1 and ATR expression. Interestingly, the previously reported participation of E2Fe in UV‐B responses, which is a transcriptional target of E2Fc, is independent and different from that described for E2Fc. Conversely, we here demonstrate that E2Fc has an epistatic role over the miR396 pathway under UV‐B conditions. Finally, we show that inhibition of cell proliferation by UV‐B is independent of the regulation of class II TCP transcription factors. Together, our results demonstrate that E2Fc is required for miR396 activity on cell proliferation under UV‐B, and that its role is independent of E2Fe, probably modulating DNA damage responses through the regulation of SOG1 and ATR transcript levels.
Significance Statement
At intensities that can induce DNA damage in Arabidopsis plants, E2Fc‐deficient plants show a lower inhibition of leaf size and an altered DNA damage response. The inhibition of plant growth by UV‐B mediated by E2Fc occurs epistatically over the microRNA396 and independently of E2Fe.
Flavonoids are widely distributed secondary metabolites with different metabolic functions in plants. The elucidation of the biosynthetic pathways, as well as their regulation by MYB, basic ...helix-loop-helix (bHLH), and WD40-type transcription factors, has allowed metabolic engineering of plants through the manipulation of the different final products with valuable applications. The present review describes the regulation of flavonoid biosynthesis, as well as the biological functions of flavonoids in plants, such as in defense against UV-B radiation and pathogen infection, nodulation, and pollen fertility. In addition, we discuss different strategies and achievements through the genetic engineering of flavonoid biosynthesis with implication in the industry and the combinatorial biosynthesis in microorganisms by the reconstruction of the pathway to obtain high amounts of specific compounds.
Summary
UV
‐B radiation inhibits plant growth, and this inhibition is, to a certain extent, regulated by miR396‐mediated repression of Growth Regulating Transcription factors (
GRF
s). Moreover, E2Fe ...transcription factor also modulates Arabidopsis leaf growth. Here, we provide evidence that, at
UV
‐B intensities that induce
DNA
damage, E2Fc participates in the inhibition of cell proliferation. We demonstrate that
E2Fc
‐deficient plants show a lower inhibition of leaf size under
UV
‐B conditions that damage
DNA
, decreased cell death after exposure and altered
SOG
1
and
ATR
expression. Interestingly, the previously reported participation of E2Fe in
UV
‐B responses, which is a transcriptional target of E2Fc, is independent and different from that described for E2Fc. Conversely, we here demonstrate that E2Fc has an epistatic role over the miR396 pathway under
UV
‐B conditions. Finally, we show that inhibition of cell proliferation by
UV
‐B is independent of the regulation of class
II TCP
transcription factors. Together, our results demonstrate that E2Fc is required for miR396 activity on cell proliferation under
UV
‐B, and that its role is independent of E2Fe, probably modulating
DNA
damage responses through the regulation of
SOG
1
and
ATR
transcript levels.
Significance Statement
At intensities that can induce
DNA
damage in Arabidopsis plants,
E2Fc
‐deficient plants show a lower inhibition of leaf size and an altered
DNA
damage response. The inhibition of plant growth by
UV
‐B mediated by E2Fc occurs epistatically over the micro
RNA
396 and independently of E2Fe.
Glycine-rich RNA-binding proteins (GRPs) are involved in the modulation of the post-transcriptional processing of transcripts and participate as an output signal of the circadian clock. However, ...neither GRPs nor the circadian rhythmic have been studied in detail in fleshy fruits as yet. In the present work, the GRP1 gene family was analysed in Micro-Tom tomato (Solanum lycopersicum L.) fruit. Three highly homologous LeGRP1 genes (LeGRP1a–c) were identified. For each gene, three products were found, corresponding to the unspliced precursor mRNA (pre-mRNA), the mature mRNA and the alternatively spliced mRNA (preLeGRP1a–c, mLeGRP1a–c and asLeGRP1a–c, respectively). Tomato GRPs (LeGRPs) show the classic RNA recognition motif and glycine-rich region, and were found in the nucleus and in the cytosol of tomato fruit. By using different Escherichia coli mutants, it was found that LeGRP1s contained in vivo RNA-melting abilities and were able to complement the cold-sensitive phenotype of BX04 cells. Particular circadian profiles of expression, dependent on the fruits’ developmental stage, were found for each LeGRP1 form. During ripening off the vine of fruits harvested at the mature green stage, the levels of all LeGRP1a–c forms drastically increased; however, incubation at 4°C prevented such increases. Analysis of the expression of all LeGRP1a–c forms suggests a positive regulation of expression in tomato fruit. Overall, the results obtained in this work reveal a complex pattern of expression of GRPs in tomato fruit, suggesting they might be involved in post-transcriptional modulation of circadian processes of this fleshy fruit.
Ribosomal protein L10 (RPL10) proteins are ubiquitous in the plant kingdom. Arabidopsis (Arabidopsis thaliana) has three RPL10 genes encoding RPL10A to RPL10C proteins, while two genes are present in ...the maize (Zea mays) genome (rpl10-1 and rpl10-2). Maize and Arabidopsis RPL10s are tissue-specific and developmentally regulated, showing high levels of expression in tissues with active cell division. Coimmunoprecipitation experiments indicate that RPL10s in Arabidopsis associate with translation proteins, demonstrating that it is a component of the 80S ribosome. Previously, ultraviolet-B (UV-B) exposure was shown to increase the expression of a number of maize ribosomal protein genes, including rpl10. In this work, we demonstrate that maize rpl10 genes are induced by UV-B while Arabidopsis RPL10s are differentially regulated by this radiation: RPL10A is not UV-B regulated, RPL10B is down-regulated, while RPL10C is up-regulated by UV-B in all organs studied. Characterization of Arabidopsis T-DNA insertional mutants indicates that RPL10 genes are not functionally equivalent. rpl10A and rpl10B mutant plants show different phenotypes: knockout rpl10A mutants are lethal, rpl10A heterozygous plants are deficient in translation under UV-B conditions, and knockdown homozygous rpl10B mutants show abnormal growth. Based on the results described here, RPL10 genes are not redundant and participate in development and translation under UV-B stress.
SUMMARY
Mediator 17 (MED17) is a subunit of the Mediator complex that regulates transcription initiation in eukaryotic organisms. In yeast and humans, MED17 also participates in DNA repair, ...physically interacting with proteins of the nucleotide excision DNA repair system, but this function in plants has not been investigated. We studied the role of MED17 in Arabidopsis plants exposed to UV‐B radiation. Our results demonstrate that med17 and OE MED17 plants have altered responses to UV‐B, and that MED17 participates in various aspects of the DNA damage response (DDR). Comparison of the med17 transcriptome with that of wild‐type (WT) plants showed that almost one‐third of transcripts with altered expression in med17 plants were also changed by UV‐B exposure in WT plants. Increased sensitivity to DNA damage after UV‐B in med17 plants could result from the altered regulation of UV‐B responsive transcripts but MED17 also physically interacts with DNA repair proteins, suggesting a direct role of this Mediator subunit during repair. Finally, we show that MED17 is necessary to regulate the DDR activated by ataxia telangiectasia and Rad3 related (ATR), and that programmed cell death 5 (PDCD5) overexpression reverts the deficiencies in DDR shown in med17 mutants. Our data demonstrate that MED17 is an important regulator of DDR after UV‐B irradiation in Arabidopsis.
Significance Statement
In Arabidopsis, MED17 regulates the DNA damage response after UV‐B exposure transcriptionally modulating the expression of genes and possibly also physically interacting with DNA repair proteins.
SUMMARYMediator 17 (MED17) is a subunit of the Mediator complex that regulates transcription initiation in eukaryotic organisms. In yeast and humans, MED17 also participates in DNA repair, physically ...interacting with proteins of the nucleotide excision DNA repair system, but this function in plants has not been investigated. We studied the role of MED17 in Arabidopsis plants exposed to UV‐B radiation. Our results demonstrate that med17 and OE MED17 plants have altered responses to UV‐B, and that MED17 participates in various aspects of the DNA damage response (DDR). Comparison of the med17 transcriptome with that of wild‐type (WT) plants showed that almost one‐third of transcripts with altered expression in med17 plants were also changed by UV‐B exposure in WT plants. Increased sensitivity to DNA damage after UV‐B in med17 plants could result from the altered regulation of UV‐B responsive transcripts but MED17 also physically interacts with DNA repair proteins, suggesting a direct role of this Mediator subunit during repair. Finally, we show that MED17 is necessary to regulate the DDR activated by ataxia telangiectasia and Rad3 related (ATR), and that programmed cell death 5 (PDCD5) overexpression reverts the deficiencies in DDR shown in med17 mutants. Our data demonstrate that MED17 is an important regulator of DDR after UV‐B irradiation in Arabidopsis.
Ribosomal protein L10 (RPL10) is an ubiquitous protein that participates in joining the 40S and 60S ribosomal subunits into a functional 80S ribosome; however, increasing evidences indicate that ...RPL10 from various organisms has multiple extra ribosomal functions, besides being a constituent of ribosome and its role in translation. Arabidopsis thaliana contains in its genome three genes encoding RPL10, named RPL10A, RPL10B and RPL10C. Previously, we found that in maize and in A. thaliana, UV-B induces a reduction in protein biosynthesis, probably as a consequence of ribosomal damage; however, cellular recovery occurs in the absence of UV-B. Here, we show that RPL10s are differentially regulated by UV-B in a dosage and time dependent manner: RPL10C is induced, RPL10B is down regulated at high UV-B intensity, and RPL10A is not UV-B regulated. In addition, by coimmunoprecipitation studies using RPL10 antibodies and proteins from control and UV-B irradiated Arabidopsis plants, we demonstrate that RPL10 associates with different proteins under the two different conditions, including nuclear proteins, suggesting that at least one isoform may have extra-ribosomal roles.
Ribosomal protein L10 (RPL10) proteins are ubiquitous in the plant kingdom. Arabidopsis (Arabidopsis thaliana) has three RPL10 genes encoding RPL10A to RPL10C proteins, while two genes are present in ...the maize (Zea mays) genome (rpl10-1 and rpl10-2). Maize and Arabidopsis RPL10s are tissue-specific and developmentally regulated, showing high levels of expression in tissues with active cell division. Coimmunoprecipitation experiments indicate that RPL10s in Arabidopsis associate with translation proteins, demonstrating that it is a component of the 80S ribosome. Previously, ultraviolet-B (UV-B) exposure was shown to increase the expression of a number of maize ribosomal protein genes, including rpl10. In this work, we demonstrate that maize rpl10 genes are induced by UV-B while Arabidopsis RPL10s are differentially regulated by this radiation: RPL10A is not UV-B regulated, RPL10B is down-regulated, while RPL10C is up-regulated by UV-B in all organs studied. Characterization of Arabidopsis T-DNA insertional mutants indicates that RPL10 genes are not functionally equivalent. rpl10A and rpl10B mutant plants show different phenotypes: knockout rpl10A mutants are lethal, rpl10A heterozygous plants are deficient in translation under UV-B conditions, and knockdown homozygous rpl10B mutants show abnormal growth. Based on the results described here, RPL10 genes are not redundant and participate in development and translation under UV-B stress.
Two isoforms of NADP-dependent malic enzyme (NADP-ME) with the same molecular mass 72 kDa and different isoelectric points, 6.1 and 6.4, were found in crude extracts from the leaves of
Aptenia ...cordifolia, a constitutive CAM plant. In the roots, only one isoform of 72 kDa was found, with a pI of 6.1. The isoform of pI 6.4 was partially purified from leaves to a final specific activity of 30.14 U mg
−1, a value similar to the photosynthetic isozymes. This enzyme showed a native mass of 264 kDa, suggesting a homotetramer. An optimal pH of 7.3 and
K
m values for NADP and
l-malate 13 μM and 1.1 mM, respectively, were determined. The enzymatic activities and the level of immunoreactive protein did not vary with the day/night cycle. The enzyme was strongly and competitively inhibited by oxaloacetate (OAA),
l-aspartate and phosphoenolpyruvate (PEP) and to a lesser degree by citrate, suggesting that NADP-ME activity might be subject to metabolite control. At night, high levels of OAA,
l-aspartate and citrate might inhibit NADP-ME, avoiding a futile cycle of carboxylation/decarboxylation mediated by PEP carboxylase, malate dehydrogenase and NADP-ME. During the day, the low levels of these metabolites would allow the decarboxylation of
l-malate.
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