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1.
Plant J ; 101(1): 171-187, 2020 01.
Article in English | MEDLINE | ID: mdl-31494998

ABSTRACT

The spikelet is the basic unit of the grass inflorescence. In tetraploid (Triticum turgidum) and hexaploid wheat (Triticum aestivum), the spikelet is a short indeterminate branch with two proximal sterile bracts (glumes) followed by a variable number of florets, each including a bract (lemma) with an axillary flower. Varying levels of miR172 and/or its target gene Q (AP2L5) result in gradual transitions of glumes to lemmas, and vice versa. Here, we show that AP2L5 and its related paralog AP2L2 play critical and redundant roles in the specification of axillary floral meristems and lemma identity. AP2L2, also targeted by miR172, displayed similar expression profiles to AP2L5 during spikelet development. Loss-of-function mutants in both homeologs of AP2L2 (henceforth ap2l2) developed normal spikelets, but ap2l2 ap2l5 double mutants generated spikelets with multiple empty bracts before transitioning to florets. The coordinated nature of these changes suggest an early role of these genes in floret development. Moreover, the flowers of ap2l2 ap2l5 mutants showed organ defects in paleas and lodicules, including the homeotic conversion of lodicules into carpels. Mutations in the miR172 target site of AP2L2 were associated with reduced plant height, more compact spikes, promotion of lemma-like characters in glumes and smaller lodicules. Taken together, our results show that the balance in the expression of miR172 and AP2-like genes is crucial for the correct development of spikelets and florets, and that this balance has been altered during the process of wheat and barley (Hordeum vulgare) domestication. The manipulation of this regulatory module provides an opportunity to modify spikelet architecture and improve grain yield.


Subject(s)
Flowers/growth & development , Flowers/metabolism , Meristem/growth & development , Meristem/metabolism , Triticum/growth & development , Triticum/metabolism , Flowers/genetics , Gene Expression Regulation, Plant/genetics , Gene Expression Regulation, Plant/physiology , Meristem/genetics , MicroRNAs/genetics , MicroRNAs/metabolism , Plant Proteins/genetics , Plant Proteins/metabolism , Triticum/genetics
2.
Nat Plants ; 1: 14016, 2015 Jan 26.
Article in English | MEDLINE | ID: mdl-27246757

ABSTRACT

The domestication of cereal crops such as wheat, maize, rice and barley has included the modification of inflorescence architecture to improve grain yield and ease harvesting(1). Yield increases have often been achieved through modifying the number and arrangement of spikelets, which are specialized reproductive branches that form part of the inflorescence. Multiple genes that control spikelet development have been identified in maize, rice and barley(2-5). However, little is known about the genetic underpinnings of this process in wheat. Here, we describe a modified spikelet arrangement in wheat, termed paired spikelets. Combining comprehensive QTL and mutant analyses, we show that Photoperiod-1 (Ppd-1), a pseudo-response regulator gene that controls photoperiod-dependent floral induction, has a major inhibitory effect on paired spikelet formation by regulating the expression of FLOWERING LOCUS T (FT)(6,7). These findings show that modulated expression of the two important flowering genes, Ppd-1 and FT, can be used to form a wheat inflorescence with a more elaborate arrangement and increased number of grain producing spikelets.

3.
Plant J ; 65(3): 382-91, 2011 Feb.
Article in English | MEDLINE | ID: mdl-21265892

ABSTRACT

Vernalization, the promotion of flowering in response to low temperatures, is one of the best characterized examples of epigenetic regulation in plants. The promotion of flowering is proportional to the duration of the cold period, but the mechanism by which plants measure time at low temperatures has been a long-standing mystery. We show that the quantitative induction of the first gene in the Arabidopsis vernalization pathway, VERNALIZATION INSENSITIVE 3 (VIN3), is regulated by the components of Polycomb Response Complex 2, which trimethylates histone H3 lysine 27 (H3K27me3). In differentiated animal cells, H3K27me3 is mostly associated with long-term gene repression, whereas, in pluripotent embyonic stem cells, many cell lineage-specific genes are inactive but exist in bivalent chromatin that carries both active (H3K4me3) and repressive (H3K27me3) marks on the same molecule. During differentiation, bivalent domains are generally resolved to an active or silent state. We found that H3K27me3 maintains VIN3 in a repressed state prior to cold exposure; this mark is not removed during VIN3 induction. Instead, active VIN3 is associated with bivalently marked chromatin. The continued presence of H3K27me3 ensures that induction of VIN3 is proportional to the duration of the cold, and that plants require prolonged cold to promote the transition to flowering. The observation that Polycomb proteins control VIN3 activity defines a new role for Polycomb proteins in regulating the rate of gene induction.


Subject(s)
Arabidopsis Proteins/physiology , Arabidopsis/physiology , Cold Temperature , Gene Expression Regulation, Plant , Acetylation , Arabidopsis/enzymology , Arabidopsis/genetics , Arabidopsis/metabolism , Arabidopsis Proteins/genetics , Arabidopsis Proteins/metabolism , Chromatin/metabolism , Chromosomal Proteins, Non-Histone/genetics , Chromosomal Proteins, Non-Histone/metabolism , DNA-Binding Proteins/genetics , DNA-Binding Proteins/metabolism , DNA-Binding Proteins/physiology , Epigenesis, Genetic , Flowers/genetics , Flowers/metabolism , Histone Acetyltransferases/metabolism , Histone-Lysine N-Methyltransferase/genetics , Histone-Lysine N-Methyltransferase/metabolism , Histone-Lysine N-Methyltransferase/physiology , Histones/metabolism , MADS Domain Proteins/genetics , MADS Domain Proteins/metabolism , Methylation , Mutation , Plants, Genetically Modified/genetics , Plants, Genetically Modified/metabolism , Plants, Genetically Modified/physiology , Polycomb-Group Proteins , Promoter Regions, Genetic/genetics , Repressor Proteins/genetics , Repressor Proteins/metabolism , Repressor Proteins/physiology , Stress, Physiological , Transcription Factors/genetics , Transcription Factors/metabolism , Transcription Factors/physiology , Up-Regulation/genetics
4.
Plant J ; 59(4): 576-87, 2009 Aug.
Article in English | MEDLINE | ID: mdl-19392705

ABSTRACT

VERNALIZATION INSENSITIVE 3 (VIN3), which is required for the vernalization-mediated epigenetic repression of FLOWERING LOCUS C (FLC) in Arabidopsis thaliana, is quantitatively induced in response to low temperatures. We found that hypoxic conditions also induce VIN3 in a quantitative manner but high salt, high temperatures and osmotic stress do not. Inhibition of mitochondrial respiration did not induce VIN3 expression, consistent with the lack of VIN3 induction in response to other stresses that affect the rate of mitochondrial respiration. De novo protein synthesis is required for VIN3 induction during hypoxic conditions; this situation is not the case for VIN3 induction by low temperatures, indicating that different mechanisms act to induce VIN3 expression in response to cold and hypoxic conditions. Without VIN3 activity, fewer seedlings survived following a 72-h period of hypoxic treatment, indicating that VIN3 is required for the survival of Arabidopsis thaliana in response to hypoxic stress. Complementation of the vin3 mutant with a VIN3 transgene restored the wild-type response to low oxygen and confirmed the role of VIN3 in protecting both shoots and roots during low oxygen conditions. Loss of VIN3 protein did not affect the transcriptional regulation of genes known to be important in the response to low oxygen stress, which suggests that there is a novel mechanism to combat hypoxia that involves VIN3. This mechanism is likely to involve chromatin remodelling and may be similar to the role of VIN3 in the epigenetic repression of FLC during the vernalization response.


Subject(s)
Arabidopsis Proteins/metabolism , Arabidopsis/genetics , DNA-Binding Proteins/metabolism , Oxygen/metabolism , Transcription Factors/metabolism , Arabidopsis/metabolism , Arabidopsis Proteins/genetics , Cell Hypoxia , Cold Temperature , Cycloheximide/pharmacology , DNA-Binding Proteins/genetics , Gene Expression Regulation, Plant , Genetic Complementation Test , Hot Temperature , Mitochondria/metabolism , Oligonucleotide Array Sequence Analysis , Osmotic Pressure , Plants, Genetically Modified/genetics , Plants, Genetically Modified/metabolism , RNA, Plant/genetics , Seedlings/genetics , Seedlings/metabolism , Sodium Chloride/pharmacology , Transcription Factors/genetics
5.
Plant J ; 44(3): 420-32, 2005 Nov.
Article in English | MEDLINE | ID: mdl-16236152

ABSTRACT

FLOWERING LOCUS C (FLC), a repressor of flowering, is a major determinant of flowering time in Arabidopsis. FLC expression is repressed by vernalization and in plants with low levels of DNA methylation, resulting in early flowering. This repression is not associated with changes of DNA methylation within the FLC locus in either vernalized plants or plants with low levels of DNA methylation. In both cases, there is a reduction of histone H3 trimethyl-lysine 4 (K4) and acetylation of both histones H3 and H4 around the promoter-translation start of FLC. The expression of the two genes flanking FLC is also repressed in both conditions and repression is associated with decreased histone H3 acetylation. The changes in histone modifications at the FLC gene cluster, which are similar in vernalized plants and in plants with reduced DNA methylation, must arise by different mechanisms. VERNALIZATION 1, VERNALIZATION 2 and VERNALIZATION INSENSITIVE 3 modulate FLC expression in vernalized plants; these proteins play no role in the downregulation of FLC in plants with low levels of DNA methylation. Chimeric FLC::GUS transgenes respond to vernalization but these same transgenes show a position-dependent response to low levels of DNA methylation. In plants with reduced DNA methylation, expression of the five MADS AFFECTING FLOWERING (MAF) genes is repressed, suggesting that DNA methylation alters the expression of a trans-acting regulator common to FLC and members of the related MAF gene family. Our observations suggest that DNA methylation is not part of the vernalization pathway.


Subject(s)
Arabidopsis Proteins/genetics , Arabidopsis/genetics , DNA Methylation , Down-Regulation , Gene Expression Regulation, Plant , MADS Domain Proteins/genetics , Acetylation , Arabidopsis/metabolism , Arabidopsis Proteins/metabolism , Chromosomes, Plant/genetics , Chromosomes, Plant/metabolism , CpG Islands , DNA-Binding Proteins/metabolism , Genome, Plant , Histones/metabolism , Introns/genetics , Plants, Genetically Modified , Seasons , Signal Transduction , Transcription Factors/metabolism , Transgenes/genetics
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