Auxin Regulation of \u3cem\u3eArabidopsis\u3c/em\u3e Flower Development Involves Members of the AINTEGUMENTA-LIKE/PLETHORA (AIL/PLT) Family

Auxin is an important regulator of many aspects of plant growth and development. During reproductive development, auxin specifies the site of flower initiation and subsequently regulates organ growth and patterning as well as later events that determine reproductive success. Underlying auxin action in plant tissues is its uneven distribution, resulting in groups of cells with high auxin levels (auxin maxima) or graded distributions of the hormone (auxin gradients). Dynamic auxin distribution within the periphery of the inflorescence meristems specifies the site of floral meristem initiation, while auxin maxima present at the tips of developing floral organ primordia probably mediate organ growth and patterning. The molecular means by which auxin accumulation patterns are converted into developmental outputs in flowers is not well understood. Members of the AINTEGUMENTA-LIKE/PLETHORA (AIL/PLT) transcription factor family are important developmental regulators in both roots and shoots. In roots, the expression of two AIL/PLT genes is regulated by auxin and these genes feed back to regulate auxin distribution. Here, several aspects of flower development involving both auxin and AIL/PLT activity are described, and evidence linking AIL/PLT function with auxin distribution in reproductive tissues is presented

\u3cem\u3eAINTEGUMENTA\u3c/em\u3e Contributes to Organ Polarity and Regulates Growth of Lateral Organs in Combination with \u3cem\u3eYABBY\u3c/em\u3e Genes

Lateral organs in flowering plants display polarity along their adaxial-abaxial axis with distinct cell types forming at different positions along this axis. Members of three classes of transcription factors in Arabidopsis (Arabidopsis thaliana; the Class III homeodomain/leucine zipper [HD-ZIP] proteins, KANADI proteins, and YABBY proteins) are expressed in either the adaxial or abaxial domain of organ primordia where they confer these respective identities. Little is known about the factors that act upstream of these polarity-determining genes to regulate their expression. We have investigated the relationship between AINTEGUMENTA (ANT), a gene that promotes initiation and growth of lateral organ primordia, and polarity genes. Although ant single mutants do not display any obvious defects in organ polarity, loss of ANT activity in combination with mutations in one or more YABBY genes results in polarity defects greater than those observed in the yabby mutants alone. Our results suggest that ANT acts in combination with the YABBY gene FILAMENTOUS FLOWER (FIL) to promote organ polarity by upregulating the expression of the adaxial-specifying HD-ZIP gene PHABULOSA. Furthermore, we show that ANT acts with FIL to up-regulate expression of the floral homeotic gene APETALA3. Our work defines new roles for ANT in the development of lateral organs

Control of Flower Size

Flowers exhibit amazing morphological diversity in many traits, including their size. In addition to interspecific flower size differences, many species maintain significant variation in flower size within and among populations. Flower size variation can contribute to reproductive isolation of species and thus has clear evolutionary consequences. In this review we integrate information on flower size variation from both evolutionary and developmental biology perspectives. We examine the role of flower size in the context of mating system evolution. In addition, we describe what is currently known about the genetic basis of flower size based on quantitative trait locus (QTL) mapping in several different plant species and molecular genetic studies in model plants, primarily Arabidopsis thaliana. Work in Arabidopsis suggests that many independent pathways regulate floral organ growth via effects on cell proliferation and/or cell expansion

\u3cem\u3eAintegumenta\u3c/em\u3e and \u3cem\u3eAintegumenta-Like6\u3c/em\u3e Regulate Auxin-Mediated Flower Development in Arabidopsis

Background: Two related genes encoding AP2/ERF-type transcription factors, AINTEGUMENTA (ANT) and AINTEGUMENTA-LIKE6 (AIL6), are important regulators of floral growth and patterning in Arabidopsis. Evidence suggests that these genes promote several aspects of flower development in response to auxin. To investigate the interplay of ANT, AIL6 and auxin during floral development, I have examined the phenotypic consequences of disrupting polar auxin transport in ant, ail6 and ant ail6 mutants by either genetic or chemical means. Results: Plants containing mutations in ANT or AIL6 alone or in both genes together exhibit increased sensitivity to disruptions in polar auxin transport. Both genes promote shoot growth, floral meristem initiation and floral meristem patterning in combination with auxin transport. However, differences in the responses of ant and ail6 single mutants to perturbations in auxin transport suggest that these two genes also have non-overlapping activities in each of these developmental processes. Conclusions: The enhanced sensitivity of ant and ail6 mutants to alterations in polar auxin transport suggests that these mutants have defects in some aspect of auxin physiology. The inability of ant ail6 double mutants to initiate flowers in backgrounds disrupted for auxin transport confirm the proposed roles for these two genes in floral meristem initiation

\u3cem\u3eAintegumenta\u3c/em\u3e and \u3cem\u3eAintegumenta-Like6\u3c/em\u3e Act Redundantly to Regulate Arabidopsis Floral Growth and Patterning

An Arabidopsis (Arabidopsis thaliana) flower consists of four types of organs arranged in a stereotypical pattern. This complex floral structure is elaborated from a small number of floral meristem cells partitioned from the shoot apical meristem during reproductive development. The positioning of floral primordia within the periphery of the shoot apical meristem depends on transport of the phytohormone auxin with floral anlagen arising at sites of auxin maxima. An early marker of lateral organ fate is the AP2/ERF-type transcription factor AINTEGUMENTA (ANT), which has been proposed to act downstream of auxin in organogenic growth. Here, I show that the related, AINTEGUMENTA-LIKE6 (AIL6)/PLETHORA3 gene acts redundantly with ANT during flower development. ant ail6 double mutants show defects in floral organ positioning, identity, and growth. These floral defects are correlated with changes in the expression levels and patterns of two floral organ identity genes, APETALA3 and AGAMOUS. ant ail6 flowers also display altered expression of an auxin-responsive reporter, suggesting that auxin accumulation and/or responses are not normal. Furthermore, I show that ANT expression in incipient and young floral primordia depends on auxin transport within the inflorescence meristem. These results show that ANT and AIL6 are important regulators of floral growth and patterning and that they may act downstream of auxin in these processes

\u3cem\u3eAINTEGUMENTA\u3c/em\u3e Promotes Petal Identity and Acts as a Negative Regulator of \u3cem\u3eAGAMOUS\u3c/em\u3e

The Arabidopsis AINTEGUMENTA (ANT) gene has been shown previously to be involved in ovule development and in the initiation and growth of floral organs. Here, we show that ANT acts in additional processes during flower development, including repression of AGAMOUS (AG) in second whorl cells, promotion of petal epidermal cell identity, and gynoecium development. Analyses of ap2-1 ant-6 double mutants reveal that ANT acts redundantly with AP2 to repress AG in second whorl cells. The abaxial surface of ant petals contains features such as stomata and elongated, interdigitated cells that are not present on wild-type petals. The loss of petal identity in these second whorl cells does not result from ectopic AG expression, suggesting that ANT acts in a pathway promoting petal cell identity that is independent of its role in repression of AG. These data suggest that ANT may function as a class A gene

Regulation of \u3cem\u3eSUP\u3c/em\u3e Expression Identifies Multiple Regulators Involved in Arabidopsis Floral Meristem Development

During the course of flower development, floral homeotic genes are expressed in defined concentric regions of floral meristems called whorls. The SUPERMAN ( SUP, also called FLO10 ) gene, which encodes a C2H2-type zinc finger protein, is involved in maintenance of the stamen/carpel whorl boundary (the boundary between whorl 3 and whorl 4) in Arabidopsis. Here, we show that the regulation of SUP expression in floral meristems is complex, consisting of two distinct phases, initiation and maintenance. The floral meristem identity gene LEAFY ( LFY ) plays a role in the initiation phase through at least two pathways, which differ from each other in the involvement of two homeotic genes, APETALA3 ( AP3 ) and PISTILLATA ( PI ). AP3 , PI , and another homeotic gene, AGAMOUS ( AG ), are further required for SUP expression in the later maintenance phase. Aside from these genes, there are other as yet unidentified genes that control both the temporal and spatial patterns of SUP expression in whorl 3 floral meristems. SUP appears to act transiently, probably functioning to trigger a genetic circuit that creates the correct position of the whorl 3/whorl 4 boundary

Aintegumenta and Aintegumenta-Like6 regulate auxin-mediated flower development in Arabidopsis

<p>Abstract</p> <p>Background</p> <p>Two related genes encoding AP2/ERF-type transcription factors, <it>AINTEGUMENTA </it>(<it>ANT</it>) and <it>AINTEGUMENTA-LIKE6 </it>(<it>AIL6</it>), are important regulators of floral growth and patterning in Arabidopsis. Evidence suggests that these genes promote several aspects of flower development in response to auxin. To investigate the interplay of <it>ANT</it>, <it>AIL6 </it>and auxin during floral development, I have examined the phenotypic consequences of disrupting polar auxin transport in <it>ant</it>, <it>ail6 </it>and <it>ant ail6 </it>mutants by either genetic or chemical means.</p> <p>Results</p> <p>Plants containing mutations in <it>ANT </it>or <it>AIL6 </it>alone or in both genes together exhibit increased sensitivity to disruptions in polar auxin transport. Both genes promote shoot growth, floral meristem initiation and floral meristem patterning in combination with auxin transport. However, differences in the responses of <it>ant </it>and <it>ail6 </it>single mutants to perturbations in auxin transport suggest that these two genes also have non-overlapping activities in each of these developmental processes.</p> <p>Conclusions</p> <p>The enhanced sensitivity of <it>ant </it>and <it>ail6 </it>mutants to alterations in polar auxin transport suggests that these mutants have defects in some aspect of auxin physiology. The inability of <it>ant ail6 </it>double mutants to initiate flowers in backgrounds disrupted for auxin transport confirm the proposed roles for these two genes in floral meristem initiation.</p

A coherent feed-forward loop drives vascular regeneration in damaged aerial organs of plants growing in a normal developmental context

Aerial organs of plants, being highly prone to local injuries, require tissue restoration to ensure their survival. However, knowledge of the underlying mechanism is sparse. In this study, we mimicked natural injuries in growing leaves and stems to study the reunion between mechanically disconnected tissues. We show that PLETHORA (PLT) and AINTEGUMENTA (ANT) genes, which encode stem cell-promoting factors, are activated and contribute to vascular regeneration in response to these injuries. PLT proteins bind to and activate the CUC2 promoter. PLT proteins and CUC2 regulate the transcription of the local auxin biosynthesis gene YUC4 in a coherent feed-forward loop, and this process is necessary to drive vascular regeneration. In the absence of this PLT-mediated regeneration response, leaf ground tissue cells can neither acquire the early vascular identity marker ATHB8, nor properly polarise auxin transporters to specify new venation paths. The PLT-CUC2 module is required for vascular regeneration, but is dispensable for midvein formation in leaves. We reveal the mechanisms of vascular regeneration in plants and distinguish between the wound-repair ability of the tissue and its formation during normal development.Peer reviewe