Search

In plants, salicylic acid (SA) hydroxylation regulates SA homoeostasis, playing an essential role during plant development and response to pathogens. This reaction is catalysed by SA hydroxylase enzymes, which hydroxylate SA producing 2,3‐dihydroxybenzoic acid (2,3‐DHBA) and/or 2,5‐dihydroxybenzoic acid (2,5‐DHBA). Several SA hydroxylases have recently been identified and characterised from different plant species, but no such activity has yet been reported in maize. In this work, we describe the identification and characterisation of a new SA hydroxylase in maize plants. This enzyme, with high sequence similarity to previously described SA hydroxylases from Arabidopsis and rice, converts SA into 2,5‐DHBA; however, it has different kinetic properties to those of previously characterised enzymes, and it also catalysers the conversion of the flavonoid dihydroquercetin into quercetin in in vitro activity assays, suggesting that the maize enzyme may have different roles in vivo to those previously reported from other species. Despite this, ZmS5H can complement the pathogen resistance and the early senescence phenotypes of Arabidopsis s3h mutant plants. Finally, we characterised a maize mutant in the S5H gene (s5hMu) that has altered growth, senescence and increased resistance against Colletotrichum graminicola infection, showing not only alterations in SA and 2,5‐DHBA but also in flavonol levels. Together, the results presented here provide evidence that SA hydroxylases in different plant species have evolved to show differences in catalytic properties that may be important to fine tune SA levels and other phenolic compounds such as flavonols, to regulate different aspects of plant development and pathogen defence. Summary statement: Maize plants express an enzyme of the 2‐oxoglutarate‐dependent oxygenase family with unique kinetic properties, having salicylic acid hydroxylase activity but it can also convert flavonols from dihydroflavonols. Zm2‐ODD7 confers increased resistance against pathogens and regulates senescence. [ABSTRACT FROM AUTHOR]

SUMMARY: Ultraviolet (UV)B radiation affects plant growth inhibiting cell proliferation. This inhibition is in part controlled by the activity of transcription factors from the E2F family. In particular, the participation of E2Fc and E2Fe in UV‐B responses in Arabidopsis plants was previously reported. However, the E2Fa and E2Fb contribution to these processes has still not been investigated. Thus, in this work, we provide evidence that, in Arabidopsis, both E2Fa and E2Fb control leaf size under UV‐B conditions without participating in the repair of cyclobutane pyrimidine dimers in the DNA. Nevertheless, in UV‐B‐exposed seedlings, E2Fa, but not E2Fb, regulates primary root elongation, cell proliferation, and programmed cell death in the meristematic zone. Using e2fa mutants that overexpress E2Fb, we showed that the role of E2Fa in the roots could not be replaced by E2Fb. Finally, our results show that E2Fa and E2Fb differentially regulate the expression of genes that activate the DNA damage response and cell cycle progression, both under conditions without UV‐B and after exposure. Overall, we showed that both E2Fa and E2Fb have different and non‐redundant roles in developmental and DNA damage responses in Arabidopsis plants exposed to UV‐B. [ABSTRACT FROM AUTHOR]

Flavonoids are plant specialized metabolites that consist of one oxygenated and two aromatic rings. Different flavonoids are grouped according to the oxidation degree of the carbon rings; they can later be modified by glycosylations, hydroxylations, acylations, methylations, or prenylations. These modifications generate a wide collection of different molecules which have various functions in plants. All flavonoids absorb in the UV wavelengths, they mostly accumulate in the epidermis of plant cells and their biosynthesis is generally activated after UV exposure. Therefore, they have been assumed to protect plants against exposure to radiation in this range. Some flavonoids also absorb in other wavelengths, for example anthocyanins, which absorb light in the visible part of the solar spectrum. Besides, some flavonoids show antioxidant properties, that is, they act as scavengers of reactive oxygen species that could be produced after high fluence UV exposure. However, to date most reports were based on in vitro studies, and there is very little in vivo evidence of how their roles are carried out. In this review we first summarize the biosynthetic pathway of flavonoids and their characteristics, and we describe recent advances on the investigation of the role of three of the most abundant flavonoids: flavonols, flavones, and anthocyanins, protecting plants against UV exposure and high light exposure. We also present examples of how using UV‐B supplementation to increase flavonoid content, is possible to improve plant nutritional and pharmaceutical values. [ABSTRACT FROM AUTHOR]

Mediator 17 (MED17) is part of the head of the Mediator complex, which regulates transcription initiation in different eukaryotic organisms, including plants. We have previously characterized MED17 roles in Arabidopsis plants exposed to UV-B radiation, revealing its involvement in various aspects of the DNA damage response after exposure. med17 mutant plants showed altered HY5 expression, which encodes a transcription factor with a central role in photomorphogenesis. Our results demonstrate that med17 mutants show altered photomorphogenic responses and also to darkness, when compared to WT plants, and these differences could be due to altered expression of genes encoding key regulators of light and darkness signaling pathways, such as HY5, COP1 and PIF3. Moreover, med17 mutants exhibit transcriptome changes similar to those previously reported in plants exposed to red and blue light, as well as those previously described for photoreceptor mutants. Interestingly, med17 and hy5 mutants show a similar set of differentially expressed genes compared to WT plants, which suggests that both proteins may participate in a common light and dark-induced signaling pathways. Together, our data provides evidence that MED17 is an important regulator of the light and darkness responses in Arabidopsis., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper, (Copyright © 2024 Elsevier B.V. All rights reserved.)