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The phytohormone auxin is essential for plant development and contributes to nearly every aspect of the plant life cycle. The spatio-temporal distribution of auxin depends on a complex interplay between auxin metabolism and cell-t...
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The phytohormone auxin is essential for plant development and contributes to nearly every aspect of the plant life cycle. The spatio-temporal distribution of auxin depends on a complex interplay between auxin metabolism and cell-to-cell auxin transport. Auxin metabolism and transport are both crucial for plant development; however, it largely remains to be seen how these processes are integrated to ensure defined cellular auxin levels or even gradients within tissues or organs. In this review, we provide a glance at very diverse topics of auxin biology, such as biosynthesis, conjugation, oxidation, and transport of auxin. This broad, but certainly superficial, overview highlights the mutual importance of auxin metabolism and transport. Moreover, it allows pinpointing how auxin metabolism and transport get integrated to jointly regulate cellular auxin homeostasis. Even though these processes have been so far only separately studied, we assume that the phytohormonal crosstalk integrates and coordinates auxin metabolism and transport. Besides the integrative power of the global hormone signaling, we additionally introduce the hypothetical concept considering auxin transport components as gatekeepers for auxin responses.
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The phytohormone auxin is a key factor in plant growth and de-velopment. Forward and reverse genetic strategies have identifiedimportant molecular components in auxin perception, signaling,and transport. These advances resulted in...
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The phytohormone auxin is a key factor in plant growth and de-velopment. Forward and reverse genetic strategies have identifiedimportant molecular components in auxin perception, signaling,and transport. These advances resulted in the identification of someof the underlying regulatory mechanisms as well as the emergenceof functional frameworks for auxin action. This review focuses onthe feedback loops that form an integrative part of these regulatorymechanisms.
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The plant hormone auxin plays a critical role in the maintenance of root stem cell niches in Arabidopsis. We have recently reported that WUSCHEL-RELATED HOMEOBOX 5 (WOX5) transcription factor modulates free auxin production in the...
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The plant hormone auxin plays a critical role in the maintenance of root stem cell niches in Arabidopsis. We have recently reported that WUSCHEL-RELATED HOMEOBOX 5 (WOX5) transcription factor modulates free auxin production in the quiescent center (QC) of the root and its expression is inhibited in a feedback-dependent manner by canonical auxin signaling that involves indole-3-acetic acid 17 (IAA17) auxin response repressor. WOX5-IAA17 feedback circuit assures the maintenance of auxin response maximum in the root tip and thereby contributes to the maintenance of distal stem cell (DSC) populations. Here, we provide evidence to show that an optimal auxin maximum in QC guided auxin signaling gradient in root tips is crucial for maintaining root DSC identity.
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Our current understanding of vein development in leaves is based on canalization of the plant hormone auxin into self-reinforcing streams which determine the sites of vascular cell differentiation. By comparison, how auxin biosynt...
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Our current understanding of vein development in leaves is based on canalization of the plant hormone auxin into self-reinforcing streams which determine the sites of vascular cell differentiation. By comparison, how auxin biosynthesis affects leaf vein patterning is less well understood. Here, after observing that inhibiting polar auxin transport rescues the sparse leaf vein phenotype in auxin biosynthesis mutants, we propose that the processes of auxin biosynthesis and cellular auxin efflux work in concert during vein development. By using computational modeling, we show that localized auxin maxima are able to interact with mechanical forces generated by the morphological constraints which are imposed during early primordium development. This interaction is able to explain four fundamental characteristics of midvein morphology in a growing leaf: (i) distal cell division; (ii) coordinated cell elongation; (iii) a midvein positioned in the center of the primordium; and (iv) a midvein which is distally branched. Domains of auxin biosynthetic enzyme expression are not positioned by auxin canalization, as they are observed before auxin efflux proteins polarize. This suggests that the site-specific accumulation of auxin, as regulated by the balanced action of cellular auxin efflux and local auxin biosynthesis, is crucial for leaf vein formation.
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The plant hormone auxin drives plant growth and morphogenesis. The levels and distribution of the active auxin indole-3-acetic acid (IAA) are tightly controlled through synthesis, inactivation, and transport. Many auxin precursors...
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The plant hormone auxin drives plant growth and morphogenesis. The levels and distribution of the active auxin indole-3-acetic acid (IAA) are tightly controlled through synthesis, inactivation, and transport. Many auxin precursors and modified auxin forms, used to regulate auxin homeostasis, have been identified; however, very little is known about the integration of multiple auxin biosynthesis and inactivation pathways. This review discusses the many ways auxin levels are regulated through biosynthesis, storage forms, and inactivation, and the potential roles modified auxins play in regulating the bioactive pool of auxin to affect plant growth and development.
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Cucurbit seedlings potentially develop a peg on each side of the transition zone between the hypocotyl and root. Seedlings grown in a horizontal position suppress the development of the peg on the upper side of the transition zone...
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Cucurbit seedlings potentially develop a peg on each side of the transition zone between the hypocotyl and root. Seedlings grown in a horizontal position suppress the development of the peg on the upper side of the transition zone in response to gravity. It is suggested that this suppression occurs due to a reduction in auxin levels to below the threshold value. We show in this study that the free indole-3-acetic acid (IAA) content is low, while IAA conjugates are significantly more abundant in the upper side of the transition zone of gravistimulated seedlings, compared to the lower side. A transient increase in mRNA of the auxin-inducible gene, CS-IAA1, was observed in the excised transition zone. The result suggests that the transition zone is a source of auxin. Cucumber seedlings treated with auxin-transport inhibitors exhibited agravitropic growth and developed a peg on each side of the transition zone. Auxin-transport inhibitors additionally caused an increase in CS-IAA1 mRNA accumulation at the transition zone, indicating a rise in intracellular auxin concentrations due to a block of auxin efflux. To study the involvement of the auxin transport system in peg formation, we isolated the cDNAs of a putative auxin influx carrier, CS-AUX1, and putative efflux carrier, CS-PIN1, from cucumber (Cucumis sativus L.) plants. Both genes (CS-AUX1 in particular) were auxin-inducible. Accumulation of CS-AUX1 and CS-PIN1 mRNAs was observed in vascular tissue, cortex and epidermis of the transition zone. A reduced level of CS-AUX1 mRNA was observed in the upper side of the gravistimulated transition zone, compared with the lower side. It is therefore possible that a balance in the activities of auxin influx and efflux carriers controls intracellular auxin concentration at the transition zone, which results in lateral placement of a peg in cucumber seedlings.
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Auxin distribution during embryogenesis and seed germination were studied with transgenic Arabidopsis plants expressing GUS gene driven by a synthetic DR5 promoter , an auxin responsive promoter. The results showed that GUS activi...
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Auxin distribution during embryogenesis and seed germination were studied with transgenic Arabidopsis plants expressing GUS gene driven by a synthetic DR5 promoter , an auxin responsive promoter. The results showed that GUS activity is higher in endsof hypophysis and cotyledon primordia of heart-, torpedo- and cotyledon-stage embryos, leaf tip area, lateral root primordia, root apex and cotyledon of young seedlings. And GUS accumulated in root apex of the seedlings grown on auxin transport inhibitor containing media. All these suggested that above-mentioned part of the organs and tissues have a higher level of auxin, and auxin polar transport inhibitor could cause the accumulation of auxin in root apex. And auxin transport inhibitor also resultedin aberration of Arabidopsis leaf pattern formation, root gravitropism and elongation.
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The incidence of auxinic herbicide resistance in plants has increased worldwide. Aux- inic herbicides were the first selective organic herbicides developed and have been used in agriculture for over 50 yr, primarily for the select...
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The incidence of auxinic herbicide resistance in plants has increased worldwide. Aux- inic herbicides were the first selective organic herbicides developed and have been used in agriculture for over 50 yr, primarily for the selective control of broadleaf weeds in cereal crops. However, the mode of action of auxinic herbicides and the molecular basis of auxinic herbicide resistance remain unknown, although an auxin-binding pro- tein(ABP)is proposed to be the primary target site.
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Polar auxin transport controls multiple aspects of plant development including differential growth, embryo and root patterning and vascular tissue differentiation. Identification of proteins involved in this process and availabili...
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Polar auxin transport controls multiple aspects of plant development including differential growth, embryo and root patterning and vascular tissue differentiation. Identification of proteins involved in this process and availability of new tools enabling `visualization' of auxin and auxin routes in planta largely contributed to the significant progress that has recently been made. New data support classical concepts, but several recent findings are likely to challenge our view on the mechanism of auxin transport. The aim of this review is to provide a comprehensive overview of the polar auxin transport field. It starts with classical models resulting from physiological studies, describes the genetic contributions and discusses the molecular basis of auxin influx and efflux. Finally, selected questions are presented in the context of developmental biology, integrating available data from different fields.
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The phytohormone auxin influences virtually all aspects of plant growth and development. Auxin transport across membranes is facilitated by, among other proteins, members of the PIN-FORMED (PIN) and the structurally similar PIN-LI...
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The phytohormone auxin influences virtually all aspects of plant growth and development. Auxin transport across membranes is facilitated by, among other proteins, members of the PIN-FORMED (PIN) and the structurally similar PIN-LIKES (PILS) families, which together govern directional cell-to-cell transport and intracellular accumulation of auxin. Canonical PIN proteins, which exhibit a polar localization in the plasma membrane, determine many patterning and directional growth responses. Conversely, the less-studied noncanonical PINs and PILS proteins, which mostly localize to the endoplasmic reticulum, attenuate cellular auxin responses. Here, and in the accompanying poster, we provide a brief summary of current knowledge of the structure, evolution, function and regulation of these auxin transport facilitators.
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