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APETALA 2-like genes AP2L2 and Q specify lemma identity and axillary floral meristem development in wheat.

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.

SUBMITTER: Debernardi JM

PROVIDER: S-EPMC6972666 | biostudies-literature | 2020 Jan

REPOSITORIES: biostudies-literature

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APETALA 2-like genes AP2L2 and Q specify lemma identity and axillary floral meristem development in wheat.

Debernardi Juan Manuel JM Greenwood Julian R JR Jean Finnegan E E Jernstedt Judy J Dubcovsky Jorge J

The Plant journal : for cell and molecular biology 20191015 1

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 p ...[more]

PMID: 31494998

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Project description:The morphological variability of the flower in angiosperms, combined with its relatively simple structure, makes it an excellent model to study cell specification and the establishment of morphogenetic patterns. Flowers are the products of floral meristems, which are determinate structures that generate four different types of floral organs before terminating. The precise organization of the flower in whorls, each defined by the identity and number of organs it contains, is controlled by a multi-layered network involving numerous transcriptional regulators. In particular, the AGAMOUS (AG) MADS domain-containing transcription factor plays a major role in controlling floral determinacy in Arabidopsis thaliana in addition to specifying reproductive organ identity. This study aims to characterize the genetic interactions between the ULTRAPETALA1 (ULT1) and LEAFY (LFY) transcriptional regulators during flower morphogenesis, with a focus on AG regulation.Genetic and molecular approaches were used to address the question of redundancy and reciprocal interdependency for the establishment of flower meristem initiation, identity and termination. In particular, the effects of loss of both ULT1 and LFY function were determined by analysing flower developmental phenotypes of double-mutant plants. The dependency of each factor on the other for activating developmental genes was also investigated in gain-of-function experiments.The ULT1 and LFY pathways, while both activating AG expression in the centre of the flower meristem, functioned independently in floral meristem determinacy. Ectopic transcriptional activation by ULT1 of AG and AP3, another gene encoding a MADS domain-containing flower architect, did not depend on LFY function. Similarly, LFY did not require ULT1 function to ectopically determine floral fate.The results indicate that the ULT1 and LFY pathways act separately in regulating identity and determinacy at the floral meristem. In particular, they independently induce AG expression in the centre of the flower to terminate meristem activity. A model is proposed whereby these independent contributions bring about a switch at the AG locus from an inactive to an active transcriptional state at the correct time and place during flower development.

Dataset Information

APETALA 2-like genes AP2L2 and Q specify lemma identity and axillary floral meristem development in wheat.

Publications

APETALA 2-like genes AP2L2 and Q specify lemma identity and axillary floral meristem development in wheat.

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