The gynoecium is the most complex floral organ, designed to protect the ovules and ensure their fertilization. Correct patterning and tissue specification in the developing gynoecium involves the ...concerted action of a host of genetic factors. In addition, apical-basal patterning into different domains, stigma and style, ovary and gynophore, appears to depend on the establishment and maintenance of asymmetric auxin distribution, with an auxin maximum at the apex. Here, we show that a small subfamily of the B3 transcription factor superfamily, the NGATHA (NGA) genes, act redundantly to specify style development in a dosage-dependent manner. Characterization of the NGA gene family is based on an analysis of the activation-tagged mutant named tower-of-pisa1 (top1), which was found to overexpress NGA3. Quadruple nga mutants completely lack style and stigma development. This mutant phenotype is likely caused by a failure to activate two auxin biosynthetic enzymes, YUCCA2 and YUCCA4, in the apical gynoecium domain. The NGA mutant phenotypes are similar to those caused by multiple combinations of mutations in STYLISH1 (STY1) and additional members of its family. NGA3/TOP1 and STY1 share almost identical patterns of expression, but they do not appear to regulate each other at the transcriptional level. Strong synergistic phenotypes are observed when nga3/top1 and sty1 mutants are combined. Furthermore, constitutive expression of both NGA3/TOP1 and STY1 induces the conversion of the ovary into style tissue. Taken together, these data suggest that the NGA and STY factors act cooperatively to promote style specification, in part by directing YUCCA-mediated auxin synthesis in the apical gynoecium domain.
In angiosperms, sexual reproduction requires a sperm cell, contained within a pollen tube, to fertilize the egg cell. The pollen tubes are capable of growth but have a difficult journey, as egg cells ...are buried within the ovary of the carpel. Several tissues, known collectively as the reproductive tract, develop within the carpel to facilitate the journey of the pollen tube. The genes involved in the formation and function of the reproductive tract have largely remained a mystery but are crucial for successful fertilization. This review summarizes recent advances in our understanding of the genetic control of reproductive tract development.
Summary
Arabidopsis has proven to be extremely useful as a reference organism for studies in plant biology, and huge efforts have been employed to unravel various mechanisms of Arabidopsis growth. A ...major challenge now is to demonstrate that this wealth of knowledge can be used for global agricultural and environmental improvement. Brassica species are closely related to Arabidopsis and represent ideal candidates for model‐to‐crop approaches as they include important crop plants, such as canola. Brassica plants normally disperse their seeds by a pod‐shattering mechanism. Although this mechanism is an advantage in nature, unsynchronized pod shatter constitutes one of the biggest problems for canola farmers. Here, we show that ectopic expression of the Arabidopsis FRUITFULL gene in Brassica juncea is sufficient to produce pod shatter‐resistant Brassica fruit and that the genetic pathway leading to valve margin specification is conserved between Arabidopsis and Brassica. These studies demonstrate a genetic strategy for the control of seed dispersal that should be generally applicable to diverse Brassica crop species to reduce seed loss.
microRNA regulation of fruit growth José Ripoll, Juan; Bailey, Lindsay J; Mai, Quynh-Anh ...
Nature plants,
03/2015, Letnik:
1, Številka:
4
Journal Article
Recenzirano
Growth is a major factor in plant organ morphogenesis and is influenced by exogenous and endogenous signals including hormones. Although recent studies have identified regulatory pathways for the ...control of growth during vegetative development, there is little mechanistic understanding of how growth is controlled during the reproductive phase. Using Arabidopsis fruit morphogenesis as a platform for our studies, we show that the microRNA miR172 is critical for fruit growth, as the growth of fruit is blocked when miR172 activity is compromised. Furthermore, our data are consistent with the FRUITFULL (FUL) MADS-domain protein and Auxin Response Factors (ARFs) directly activating the expression of a miR172-encoding gene to promote fruit valve growth. We have also revealed that MADS-domain (such as FUL) and ARF proteins directly associate in planta. This study defines a novel and conserved microRNA-dependent regulatory module integrating developmental and hormone signalling pathways in the control of plant growth.
Proper development of petals and stamens in Arabidopsis flowers requires the activities of APETALA3 (AP3) and PISTILLATA (PI), whose transcripts can be detected in the petal and stamen primordia. ...Localized expression of AP3 and PI requires the activities of at least three genes: APETALA1 (AP1), LEAFY (LFY), and UNUSUAL FLORAL ORGANS (UFO). It has been proposed that UFO provides spatial cues and that LFY specifies competence for AP3 and PI expression in the developing flower. To understand the epistatic relationship among AP1, LFY, and UFO in regulating AP3 and PI expression, we generated two versions of AP1 that have strong transcriptional activation potential. Genetic and molecular analyses of transgenic plants expressing these activated AP1 proteins show that the endogenous AP1 protein acts largely as a transcriptional activator in vivo and that AP1 specifies petals by regulating the spatial domains of AP3 and PI expression through UFO.
More than 200 years ago, Goethe proposed that each of the distinct flower organs represents a modified leaf 1. Support for this hypothesis has come from genetic studies, which have identified genes ...required for flower organ identity. These genes have been incorporated into the widely accepted ABC model of flower organ identity, a model that appears generally applicable to distantly related eudicots as well as monocot plants. Strikingly, triple mutants lacking the ABC activities produce leaves in place of flower organs, and this finding demonstrates that these genes are required for floral organ identity 2. However, the ABC genes are not sufficient for floral organ identity since ectopic expression of these genes failed to convert vegetative leaves into flower organs. This finding suggests that one or more additional factors are required 3, 4. We have recently shown that SEPALLATA (SEP) represents a new class of floral organ identity genes since the loss of SEP activity results in all flower organs developing as sepals 5. Here we show that the combined action of the SEP genes, together with the A and B genes, is sufficient to convert leaves into petals.
The fruit is a highly specialized plant organ that occurs in diverse forms
among the angiosperms. Fruits of
Arabidopsis thaliana
, which are typical
of the >3000 species of Brassicaceae, develop from ...a gynoecium that consists
of two fused carpels. The mature gynoecium of
Arabidopsis
is composed of
an apical stigma, a short style, and a basal ovary that contains the developing
ovules. After the ovules are fertilized, the fruit elongates and differentiates
a number of distinct cell types, allowing for the successful maturation and the
eventual dispersal of the seeds. Although the processes involved in carpel and
fruit morphogenesis are not well understood, recent studies have identified a
large number of mutants that display abnormal gynoecium and fruit development.
The detailed phenotypic description of these mutants together with recent
cloning of many of these genes has begun to shed light on this interesting and
complex developmental process. Here we review the growing collection of
Arabidopsis
genes known to control the initiation and development of the
gynoecium and resulting fruit.
The first step in flower development is the transition of an inflorescence meristem into a floral meristem. Each floral meristem differentiates into a flower consisting of four organ types that ...occupy precisely defined positions within four concentric whorls. Genetic studies in Arabidopsis thaliana and Antirrhinum majus have identified early-acting genes that determine the identify of the floral meristem, and late-acting genes that determine floral organ identity. In Arabidopsis, at least two genes, APETALA1 and LEAFY, are required for the transition of an influorescence meristem into a floral meristem. We have cloned the APETALA1 gene and here we show that it encodes a putative transcription factor that contains a MADS-domain. APETALA1 RNA is uniformly expressed in young flower primordia, and later becomes localized to sepals and petals. Our results suggest that APETALA1 acts locally to specify the identity of the floral meristem, and to determine sepal and petal development.
The Arabidopsis gene AGAMOUS is required for male and female reproductive organ development and for floral determinacy. Reverse genetics allowed the isolation of a transposon-induced mutation in ...ZAG1, the maize homolog of AGAMOUS. ZAG1 mutants exhibited a loss of determinacy, but the identity of reproductive organs was largely unaffected. This suggested a redundancy in maize sex organ specification that led to the identification and cloning of a second AGAMOUS homolog, ZMM2, that has a pattern of expression distinct from that of ZAG1. C-function organ identify in maize (as defined by the A, B, C model of floral organ development) may therefore be orchestrated by two closely related genes, ZAG1 and ZMM2, with overlapping but nonidentical activities.
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