Abstract
Plant hormone biology is an ever-evolving field and as such, novel avenues of research must always be sought. Technological and theoretical advancement can also allow for previously ...dismissed research to yield equally interesting insights into processes now that they are better understood. The auxin phenylacetic acid (PAA) is an excellent example of this. PAA is a plant auxin that also possesses substantial antimicrobial activity. It has a broad distribution and has been studied in bacteria, fungi, algae and land plants. Research on this compound in plants was prominent in the 1980s, where its bioactivity and broad distribution were frequently examined. Unfortunately, due to the strong interest in the quintessential auxin, indole-3-acetic acid (IAA), research on PAA quickly petered out. Recently, several groups have resumed investigations on this hormone in plants, yet, little is known about PAA biology and its physiological role is unclear. PAA biosynthesis from the amino acid Phe invites direct comparisons with previously studied IAA biosynthesis pathways, and recent work has shown that PAA metabolism and signaling appears to be similar to that of IAA. However, given the large gap between previous work and recent investigations, a historical review of this auxin is required to renew our understanding of PAA. Here, previous work on PAA is reassessed in light of recent research in plants and serves as a synthesis of current knowledge on PAA biology.
The phytohormone auxin (indole-3-acetic acid IAA) plays a fundamental role in vegetative and reproductive plant development. Here, we characterized a seed-specific viable maize (Zea mays) mutant, ...defective endosperm18 (de18) that is impaired in IAA biosynthesis, de18 endosperm showed large reductions of free IAA levels and is known to have approximately 40% less dry mass, compared with De18. Cellular analyses showed lower total cell number, smaller cell volume, and reduced level of endoreduplication in the mutant endosperm. Gene expression analyses of seed-specific tryptophan-dependent IAA pathway genes, maize Yucca1 (ZmYuc1), and two tryptophan-aminotransferase co-orthologs were performed to understand the molecular basis of the IAA deficiency in the mutant. Temporally, all three genes showed high expression coincident with high IAA levels; however, only ZmYuc1 correlated with the reduced IAA levels in the mutant throughout endosperm development. Furthermore, sequence analyses of ZmYuc1 complementary DNA and genomic clones revealed many changes specific to the mutant, including a 2-bp insertion that generated a premature stop codon and a truncated YUC1 protein of 212 amino acids, compared with the 400 amino acids in the De18. The putative, approximately 1.5-kb, Yuc1 promoter region also showed many rearrangements, including a 151-bp deletion in the mutant. Our concurrent high-density mapping and annotation studies of chromosome 10, contig 395, showed that the De18 locus was tightly linked to the gene ZmYuc1. Collectively, the data suggest that the molecular changes in the ZmYuc1 gene encoding the YUC1 protein are the causal basis of impairment in a critical step in IAA biosynthesis, essential for normal endosperm development in maize.
With climate change, droughts are expected to be more frequent and severe, severely impacting plant biomass and quality. Here, we show that overexpressing the Arabidopsis gene AtFtsHi3 (FtsHi3OE) ...enhances drought‐tolerant phenotypes without compromising plant growth. AtFtsHi3 encodes a chloroplast envelope pseudo‐protease; knock‐down mutants (ftshi3‐1) are found to be drought tolerant but exhibit stunted growth. Altered AtFtsHi3 expression therefore leads to drought tolerance, while only diminished expression of this gene leads to growth retardation. To understand the underlying mechanisms of the enhanced drought tolerance, we compared the proteomes of ftshi3‐1 and pFtsHi3‐FtsHi3OE (pFtsHi3‐OE) to wild‐type plants under well‐watered and drought conditions. Drought‐related processes like osmotic stress, water transport, and abscisic acid response were enriched in pFtsHi3‐OE and ftshi3‐1 mutants following their enhanced drought response compared to wild‐type. The knock‐down mutant ftshi3‐1 showed an increased abundance of HSP90, HSP93, and TIC110 proteins, hinting at a potential downstream role of AtFtsHi3 in chloroplast pre‐protein import. Mathematical modeling was performed to understand how variation in the transcript abundance of AtFtsHi3 can, on the one hand, lead to drought tolerance in both overexpression and knock‐down lines, yet, on the other hand, affect plant growth so differently. The results led us to hypothesize that AtFtsHi3 may form complexes with at least two other protease subunits, either as homo‐ or heteromeric structures. Enriched amounts of AtFtsH7/9, AtFtsH11, AtFtsH12, and AtFtsHi4 in ftshi3‐1 suggest a possible compensation mechanism for these proteases in the hexamer.
One of the fundamental plant growth substances, indole-3-acetic acid (IAA), belongs to a class of phytohormones known as auxins. The main IAA biosynthesis pathway involves the conversion of ...tryptophan to indole-3-pyruvic acid, which is in turn converted to IAA. The two enzymes responsible for these conversions, members of the TAA1 and YUCCA gene families, respectively, have recently been implicated in the synthesis of another auxin, phenylacetic acid (PAA). While there is some evidence to support this theory, there are also some concerns. Here we address the question: to what extent does the TAA1/YUCCA system contribute to the biosynthesis of PAA? In addition, we highlight the importance of measuring auxin metabolites and conjugates in addressing such questions.
The biosynthesis of the main auxin in plants (indole-3-acetic acid IAA) has been elucidated recently and is thought to involve the sequential conversion of Trp to indole-3-pyruvic acid to IAA. ...However, the pathway leading to a less well studied auxin, phenylacetic acid (PAA), remains unclear. Here, we present evidence from metabolism experiments that PAA is synthesized from the amino acid Phe, via phenylpyruvate. In pea (Pisum sativum), the reverse reaction, phenylpyruvate to Phe, is also demonstrated. However, despite similarities between the pathways leading to IAA and PAA, evidence from mutants in pea and maize (Zea mays) indicate that IAA biosynthetic enzymes are not the main enzymes for PAA biosynthesis. Instead, we identified a putative aromatic aminotransferase (PsArAT) from pea that may function in the PAA synthesis pathway.
Abstract
Auxin is the first discovered plant hormone and is essential for many aspects of plant growth and development. Indole-3-acetic acid (IAA) is the main auxin and plays pivotal roles in ...intercellular communication through polar auxin transport. Phenylacetic acid (PAA) is another natural auxin that does not show polar movement. Although a wide range of species have been shown to produce PAA, its biosynthesis, inactivation and physiological significance in plants are largely unknown. In this study, we demonstrate that overexpression of the CYP79A2 gene, which is involved in benzylglucosinolate synthesis, remarkably increased the levels of PAA and enhanced lateral root formation in Arabidopsis. This coincided with a significant reduction in the levels of IAA. The results from auxin metabolite quantification suggest that the PAA-dependent induction of GRETCHEN HAGEN 3 (GH3) genes, which encode auxin-amido synthetases, promote the inactivation of IAA. Similarly, an increase in IAA synthesis, via the indole-3-acetaldoxime pathway, significantly reduced the levels of PAA. The same adjustment of IAA and PAA levels was also observed by applying each auxin to wild-type plants. These results show that GH3 auxin-amido synthetases can alter the ratio of IAA and PAA in plant growth and development.
Land plants lose vast quantities of water to the atmosphere during photosynthetic gas exchange. In angiosperms, a complex network of veins irrigates the leaf, and it is widely held that the density ...and placement of these veins determines maximum leaf hydraulic capacity and thus maximum photosynthetic rate. This theory is largely based on interspecific comparisons and has never been tested using vein mutants to examine the specific impact of leaf vein morphology on plant water relations. Here we characterize mutants at the Crispoid (Crd) locus in pea (Pisum sativum), which have altered auxin homeostasis and activity in developing leaves, as well as reduced leaf vein density and aberrant placement of free-ending veinlets. This altered vein phenotype in crd mutant plants results in a significant reduction in leaf hydraulic conductance and leaf gas exchange. We find Crispoid to be a member of the YUCCA family of auxin biosynthetic genes. Our results link auxin biosynthesis with maximum photosynthetic rate through leaf venation and substantiate the theory that an increase in the density of leaf veins coupled with their efficient placement can drive increases in leaf photosynthetic capacity.
Since the adoption of UN Security Council Resolution 1325, the woman-in-conflict has emerged as a central figure in the discourse of the UNSC Women, Peace and Security policy community. She is an ...ever-present referent in discussions, the person in whose name critique is launched or action demanded. This figure is a representation of the needs and interests of the uncountable, faceless and nameless women affected by and living through war; a representation that takes place through imbuing her with particular meaning or characteristics. These meanings shape how the figure is understood in Women, Peace and Security discourse, which, in turn, constructs the horizons of possibility for both current and future policy and its implementation. This article explores how this figure is produced as a subject through layers of representation and is deeply embedded in the practices and relationships of power in the policy community. It suggests that accounting for these will offer an opportunity for feminist advocates to engage in this institutional space in more considered and effective ways.
•Family landowners could play a significant role in mitigating climate change.•Aligning scientific and public views on forest management is crucial for increasing the participation of family forest ...landowners in voluntary forest carbon programs.•A divergence exists regarding the carbon potential of using genetically advanced species to enhance carbon in forestlands.•A convergence exists in using improved forest management to increase carbon stocks.•Conservation-based carbon approaches could result in greater participation in voluntary carbon programs.
Aligning scientific and public views on forest management is crucial for increasing the participation of family forest landowners in voluntary forest carbon programs. We compared the results from a systematic literature review of forty research articles in the US South with the perceptions of the stakeholder groups. We quantified perceptions of stakeholder groups regarding the potential of different forest management practices to enhance the carbon stocks in family forestlands by undertaking surveys in a total of two workshops conducted in the South and North Carolinas. We found a clear divergence regarding the carbon potential of the use of genetically advanced species for enhancing carbon. The workshop attendees did not rank this option high, although it is highly prioritized in the scientific literature. Convergence in using improved forest management to increase carbon stocks was observed. Although extended rotation was favored as the second-to-last option for enhancing carbon (before better genetics) by workshop respondents, non-landowners ranked it a higher priority than landowners. All workshop attendees ranked afforestation overall highest, corroborating the systematic review studies in the US South. The workshop attendees suggested conservation-based forest carbon management as a potential option to enhance the carbon stocks in family forestlands; however, we did not find much scientific literature on this option. This study is beneficial to both forest landowners and managers of forest carbon programs as well as to the scientific community at large. It brings all stakeholder groups together to craft new carbon programs for broader participation and carbon stock enhancement in the US South (and beyond).
Abstract
Feminist interventions in international politics are, more often than not, understood (and visible) as interventions in relation to policy documents. These policies—in this case the United ...Nations Security Council's resolutions on Women, Peace and Security—often feature as the end point of feminist advocacy efforts or as the starting point for feminist analysis and critique. In this article the author responds to the provocations throughout Marysia Zalewski's work to think (and tell) the spaces of international politics differently, in this case by working with the concept of feminist failure as it is produced in feminist policy critique. Inspired by Zalewski's Feminist International Relations: exquisite corpse, the article explores the material and imaginary spaces in which both policies and critique are produced. It picks up and reflects upon a narrative refrain recognizable in feminist critiques on Women, Peace and Security policy—that we must not make war safe for women—as a way to reflect on the inevitability of failure and the ostensible boundaries between theory and practice. The author takes permission from Zalewski's creative interventions and her recognition of the value of the ‘detritus of the everyday’—here a walk from New York's Grand Central Station to the UN Headquarters, musings on the flash of a particular shade of blue, and the contents of a footnoted acknowledgement, begin to trace an international political space that is produced through embodied and quotidian practice.
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