http://disciplinas.stoa.usp.br/pluginfile.php/87477/mod_resource/content/1/Plant%20Sci%202012%20Agati%20G.pdf

Flavonoids as antioxidants in plants: Location and functional significance

https://www.cell.com/cell/pdf/S0092-8674(09)00258-X.pdf

Auxin: a trigger for change in plant development.

The differential distribution of the plant signaling molecule auxin is required for many aspects of plant development. Local auxin maxima and gradients arise as a result of local auxin metabolism and, predominantly, from directional cell-to-cell transport. In this primer, we discuss how the coordinated activity of several auxin influx and efflux systems, which transport auxin across the plasma membrane, mediates directional auxin flow. This activity crucially contributes to the correct setting of developmental cues in embryogenesis, organogenesis, vascular tissue formation and directional growth in response to environmental stimuli.

/pdf/auxin-transport-routes-in-plant-development-aec7t162ch.pdf

Auxin transport routes in plant development.

Auxin participates in a multitude of developmental processes, as well as responses to environmental cues. Compared with other plant hormones, auxin exhibits a unique property, as it undergoes directional, cell-to-cell transport facilitated by plasma membrane-localized transport proteins. Among them, a prominent role has been ascribed to the PIN family of auxin efflux facilitators. PIN proteins direct polar auxin transport on account of their asymmetric subcellular localizations. In this review, we provide an overview of the multiple developmental roles of PIN proteins, including the atypical endoplasmic reticulum-localized members of the family, and look at the family from an evolutionary perspective. Next, we cover the cell biological and molecular aspects of PIN function, in particular the establishment of their polar subcellular localization. Hormonal and environmental inputs into the regulation of PIN action are summarized as well.

/pdf/pin-dependent-auxin-transport-action-regulation-and-3y6sor4k5e.pdf

PIN-Dependent Auxin Transport: Action, Regulation, and Evolution

Auxin conjugates are thought to play important roles as storage forms for the active plant hormone indole-3-acetic acid (IAA). In its free form, IAA comprises only up to 25% of the total amount of IAA, depending on the tissue and the plant species studied. The major forms of IAA conjugate are low molecular weight ester or amide forms, but there is increasing evidence of the occurrence of peptides and proteins modified by IAA. Since the discovery of genes and enzymes involved in synthesis and hydrolysis of auxin conjugates, much knowledge has been gained on the biochemistry and function of these compounds, but there is still much to discover. For example, recent work has shown that some auxin conjugate hydrolases prefer conjugates with longer-chain auxins such as indole-3-propionic acid and indole-3-butyric acid as substrate. Also, the compartmentation of these reactions in the cell or in tissues has not been resolved in great detail. The function of auxin conjugates has been mainly elucidated by mutant analysis in genes for synthesis or hydrolysis and a possible function for conjugates inferred from these results. In the evolution of land plants auxin conjugates seem to be connected with the development of certain traits such as embryo, shoot, and vasculature. Most likely, the synthesis of auxin conjugates was developed first, since it has been already detected in moss, whereas sequences typical of auxin conjugate hydrolases were found according to database entries first in moss ferns. The implications for the regulation of auxin levels in different species will be discussed.

Auxin conjugates: their role for plant development and in the evolution of land plants

The plant signalling molecule auxin provides positional information in a variety of developmental processes by means of its differential distribution (gradients) within plant tissues. Thus, cellular auxin levels often determine the developmental output of auxin signalling. Conceptually, transmembrane transport and metabolic processes regulate the steady-state levels of auxin in any given cell. In particular, PIN auxin-efflux-carrier-mediated, directional transport between cells is crucial for generating auxin gradients. Here we show that Arabidopsis thaliana PIN5, an atypical member of the PIN gene family, encodes a functional auxin transporter that is required for auxin-mediated development. PIN5 does not have a direct role in cell-to-cell transport but regulates intracellular auxin homeostasis and metabolism. PIN5 localizes, unlike other characterized plasma membrane PIN proteins, to endoplasmic reticulum (ER), presumably mediating auxin flow from the cytosol to the lumen of the ER. The ER localization of other PIN5-like transporters (including the moss PIN) indicates that the diversification of PIN protein functions in mediating auxin homeostasis at the ER, and cell-to-cell auxin transport at the plasma membrane, represent an ancient event during the evolution of land plants.

Subcellular homeostasis of phytohormone auxin is mediated by the ER-localized PIN5 transporter

The signalling molecule auxin controls plant morphogenesis via its activity gradients, which are produced by intercellular auxin transport. Cellular auxin efflux is the rate-limiting step in this process and depends on PIN and phosphoglycoprotein (PGP) auxin transporters. Mutual roles for these proteins in auxin transport are unclear, as is the significance of their interactions for plant development. Here, we have analysed the importance of the functional interaction between PIN- and PGP-dependent auxin transport in development. We show by analysis of inducible overexpression lines that PINs and PGPs define distinct auxin transport mechanisms: both mediate auxin efflux but they play diverse developmental roles. Components of both systems are expressed during embryogenesis, organogenesis and tropisms, and they interact genetically in both synergistic and antagonistic fashions. A concerted action of PIN- and PGP-dependent efflux systems is required for asymmetric auxin distribution during these processes. We propose a model in which PGP-mediated efflux controls auxin levels in auxin channel-forming cells and, thus, auxin availability for PIN-dependent vectorial auxin movement.

Interaction of PIN and PGP transport mechanisms in auxin distribution-dependent development

The plant signaling molecule auxin provides positional and
directional information in a wide variety of developmental
processes via its differential distribution (gradients) within
plant tissues1. Thus cellular auxin levels often decide about
the developmental output of auxin signaling. Conceptually,
transmembrane transport and metabolic processes regulate the
steady-state levels of auxin in any given cell2. In particular,
PIN auxin efflux carrier-mediated, directional auxin transport
between cells is crucial for generating intercellular auxin
distribution3. Here we show that Arabidopsis thaliana PIN5, -
an atypical member of the PIN gene family encodes a functional
auxin transporter that is required for auxin-mediated
development but does not play a direct role in cell-to-cell
transport. Instead, PIN5 is an important factor in controlling
intracellular auxin homeostasis and metabolism. PIN5 localizes,
unlike other characterized plasma membrane PIN proteins, to
endoplasmatic reticulum (ER) presumably mediating auxin flow
from the cytosol to the lumen of ER. The ER localization of
other PIN5-like transporters including the moss PIN suggests
that the diversification of PIN protein functions in mediating
auxin homeostasis and cell-to-cell auxin transport represents
an ancient event during the evolution of land plants. Sequence
manipulation revealed that PIN functional diversification could
have been realized by a small sequence modification in
conserved residues leading to a change in subcellular protein
sorting. Our data identified an additional mode of regulating
homeostasis of a plant hormone by its subcellular
compartmentalization and provide insights into evolution of
mechanisms controlling auxin homeostasis and transport.

Vassilena Gaykova

Papers

Subcellular homeostasis of phytohormone auxin is mediated by the ER-localized PIN5 transporter

Interaction of PIN and PGP transport mechanisms in auxin distribution-dependent development

ER-localized PIN5 auxin transporter mediates subcellularhomeostasis of phytohormone auxin