A fascinating aspect of floral diversity is the dramatic difference in flower size observed in nature. The largest flowers in the world, Rafflesia arnoldii, span several feet while flowers of the ...genus Wolffia are microscopic. My own particular interest in flower size started when I overexpressed the Arabidopsis gene AINTEGUMENTA (ANT) and observed a larger flower phenotype.
A classical role of the hormone auxin is in the formation of flowers at the periphery of the reproductive shoot apex. Mutants in regulators of polar auxin transport or in the auxin-responsive ...transcription factor MONOPTEROS (MP) form naked inflorescence “pins” lacking flowers. How auxin maxima and MP direct initiation of flower primordia is poorly understood. Here, we identify three genes whose expression is directly induced by auxin-activated MP that furthermore jointly regulate flower primordium initiation. These three genes encode known regulators of flower development: LEAFY (LFY), which specifies floral fate, and two AINTEGUMENTA-LIKE/PLETHORA transcription factors, key regulators of floral growth. Our study thus reveals a mechanistic link between flower primordium initiation and subsequent steps in flower morphogenesis. Finally, we uncover direct positive feedback from LFY to the auxin pathway. The auxin LFY module we describe may have been recruited during evolution to pattern other plant organ systems.
Display omitted
► Auxin-activated MP directly induces key floral regulators LFY, ANT, and AIL6 ► The LFY promoter contains conserved biologically relevant auxin response elements ► LFY, ANT, and AIL6 have redundant roles in flower primordium initiation ► LFY feeds back to the auxin pathway at least in part by directly inducing PID
Yamaguchi et al. identify three flower development regulators, including the floral fate specification factor LEAFY, as targets of the auxin-responsive transcription factor MONOPTEROS and uncover positive feedback from LEAFY to the auxin pathway. These findings elucidate a regulatory framework for flower primoridium initiation by auxin and coordination with flower morphogenesis.
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.
AINTEGUMENTA (ANT) is an important regulator of Arabidopsis flower development that has overlapping functions with the related AINTEGUMENTA-LIKE6 (AIL6) gene in floral organ initiation, identity ...specification, growth, and patterning. Two other AINTEGUMENTA-LIKE (AIL) genes, AIL5 and AIL7, are expressed in developing flowers in spatial domains that partly overlap with those of ANT. Here, it is shown that AIL5 and AIL7 also act in a partially redundant manner with ANT. The results demonstrate that AIL genes exhibit unequal genetic redundancy with roles for AIL5, AIL6, and AIL7 only revealed in the absence of ANT function. ant ail5 and ant ail7 double mutant flowers show alterations in floral organ positioning and growth, sepal fusion, and reductions in petal number. In ant ail5, petals are often replaced by filaments or dramatically reduced in size. ant ail7 double mutants produce increased numbers of carpels, which have defects in valve fusion and a loss of apical tissues. The distinct phenotypes of ant ail5, ant ail7 and the previously characterized ant ail6 indicate that AIL5, AIL6, and AIL7 make unique contributions to flower development. These distinct roles are also supported by genetic analyses of ant ail triple mutants. While ant ail5 ail6 triple mutants closely resemble ant ail6 double mutants, ant ail5 ail7 triple mutants exhibit more severe deviations from the wild type than either ant ail5 or ant ail7 double mutants. Furthermore, it is shown that AIL5, AIL6, and AIL7 act in a dose dependent manners in ant and other mutant backgrounds.
Display omitted
•AIL/PLTs promote growth and division and oppose differentiation in roots and shoots.•Despite common functions, AIL/PLT target genes may differ in roots and shoots.•The root AIL/PLT ...target genes translate a persistent auxin maximum into patterned cell division and cell differentiation zones.
Growth at the root tip and organ generation at the shoot tip depend on the proper functioning of apical meristems and the transitioning of meristematic cell descendants from a proliferating state to cell elongation and differentiation. Members of the AINTEGUMENTA-LIKE/PLETHORA (AIL/PLT) transcription factor family, a clade of two-AP2 domain proteins, specify both stem cell fate and control cellular progression of stem cell daughter cells toward differentiation. Here we highlight the importance of an AIL/PLT protein gradient in controlling distinct cellular behaviors in the root through the regulation of distinct targets in different parts of the root tip. Within the shoot, AIL/PLT proteins also promote organ growth and inhibit differentiation pointing to conserved roles in meristem function. However, they exhibit unequal genetic redundancy in these functions and do not always act in a purely additive manner. Differences in AIL/PLT regulation and perhaps transcriptional targets in roots and shoots suggest that these growth regulators have adapted to mediate growth control in distinct ways in these organ systems.
An afternoon stroll through an English garden reveals the breathtaking beauty and enormous diversity of flowering plants. The extreme variation of flower morphologies, combined with the relative ...simplicity of floral structures and the wealth of floral mutants available, has made the flower an excellent model for studying developmental cell-fate specification, morphogenesis and tissue patterning. Recent molecular genetic studies have begun to reveal the transcriptional regulatory cascades that control early patterning events during flower formation, the dynamics of the gene-regulatory interactions, and the complex combinatorial mechanisms that create a distinct final floral architecture and form.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
SUMMARY
Understanding how flowers form is an important problem in plant biology, as human food supply depends on flower and seed production. Flower development also provides an excellent model for ...understanding how cell division, expansion and differentiation are coordinated during organogenesis. In the model plant Arabidopsis thaliana, floral organogenesis requires AINTEGUMENTA (ANT) and AINTEGUMENTA‐LIKE 6 (AIL6)/PLETHORA 3 (PLT3), two members of the Arabidopsis AINTEGUMENTA‐LIKE/PLETHORA (AIL/PLT) transcription factor family. Together, ANT and AIL6/PLT3 regulate aspects of floral organogenesis, including floral organ initiation, growth, identity specification and patterning. Previously, we used RNA‐Seq to identify thousands of genes with disrupted expression in ant ail6 mutant flowers, indicating that ANT and AIL6/PLT3 influence a vast transcriptional network. The immediate downstream targets of ANT and AIL6/PLT3 in flowers are unknown, however. To identify direct targets of ANT regulation, we performed an RNA‐Seq time‐course experiment in which we induced ANT activity in transgenic plants bearing an ANT‐glucocorticoid receptor fusion construct. In addition, we performed a ChIP‐Seq experiment that identified ANT binding sites in developing flowers. These experiments identified 200 potential ANT target genes based on their proximity to ANT binding sites and differential expression in response to ANT. These 200 candidate target genes were involved in functions such as polarity specification, floral organ development, meristem development and auxin signaling. In addition, we identified several genes associated with lateral organ growth that may mediate the role of ANT in organ size control. These results reveal new features of the ANT transcriptional network by linking ANT to previously unknown regulatory targets.
Significance Statement
Flower development has been extensively studied, but our knowledge of gene regulatory networks generating floral organs with characteristic forms remains incomplete. This study used a highly targeted genomic approach to identify 200 genes likely to be direct targets of regulation by AINTEGUMENTA (ANT), a transcription factor regulating flower patterning and growth. Our set of identified target genes include those with known roles in polarity specification, floral organ development, lateral organ growth and auxin signaling.
Proper timing of the onset to flower formation is critical for reproductive success. Monocarpic plants like Arabidopsis (Arabidopsis thaliana) switch from production of branches in the axils of ...leaves to that of flowers once in their lifecycle, during the meristem identity transition. The plant-specific transcription factor LEAFY (LFY) is necessary and sufficient for this transition. Previously, we reported that the plant hormone auxin induces LFY expression through AUXIN RESPONSE FACTOR5/MONOPTEROS (ARF5/MP). It is not known whether MP is solely responsible for auxin-directed transcriptional activation of LFY. Here, we show that two transcription factors belonging to the AINTEGUMENTA-LIKE/PLETHORA family, AINTEGUMENTA (ANT) and AINTEGUMENTA-LIKE6/PLETHORA3 (AIL6/PLT3), act in parallel with MP to upregulate LFY in response to auxin. ant ail6 mutants display a delay in the meristem identity transition and in LFY induction. ANT and AIL6/PLT3 are expressed prior to LFY and bind to the LFY promoter to control LFY mRNA accumulation. Genetic and promoter/reporter studies suggest that ANT/AIL6 act in parallel with MP to promote LFY induction in response to auxin sensing. Our study highlights the importance of two separate auxin-controlled pathways in the meristem identity transition.
Three members of the Arabidopsis AINTEGUMENTA-LIKE/PLETHORA (AIL/PLT) transcription factor family, AIL5/PLT5, AIL6/PLT3, and AIL7/PLT7, exhibit partially overlapping roles with AINTEGUMENTA (ANT) ...during flower development. Loss of
ANT
function alone results in smaller floral organs and female sterility indicating that some ANT functions cannot be provided by these related transcription factors. Previously, we showed that expression of
AIL6
at the same levels and spatial pattern as
ANT
could largely rescue the defects of
ant
mutants. This suggested that the functional differences between
ANT
and
AIL6
were primarily a consequence of expression differences. Here, we investigated the functional differences between
ANT
and both
AIL5
and
AIL7
by expressing these two
AIL
s under the control of the
ANT
promoter. We found that only
ANT:gAIL5
lines with much higher amounts of
AIL5
mRNA as compared with
ANT
could compensate for loss of
ANT
function.
ANT:gAIL7
lines with
AIL7
mRNA levels similar to those of
ANT
were able to rescue some but not all aspects of the
ant
mutant phenotype. Thus, expression differences alone cannot explain the functional differences between ANT and these two related proteins. Studies in yeast show that AIL5 and AIL7 have lower transcriptional activation activities as compared with ANT and AIL6 when bound to the consensus ANT DNA binding site. Our results suggest that differences in both expression and protein activity contribute to the functional specificity of ANT compared with AIL5 and AIL7.
Key message
The distinct contributions of the related Arabidopsis transcription factors ANT, AIL5, and AIL7 in flower development result from differences in both expression and protein activity.
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.
PDF
