The Striking Flower-in-Flower Phenotype of Arabidopsis thaliana Nossen (No-0) is Caused by a Novel LEAFY Allele

Abstract

The transition to reproduction is a crucial step in the life cycle of any organism. In Arabidopsis thaliana the establishment of reproductive growth can be divided into two phases: Firstly, cauline leaves with axillary meristems are formed and internode elongation begins. Secondly, lateral meristems develop into flowers with defined organs. Floral shoots are usually determinate and suppress the development of lateral shoots. Here, we describe a transposon insertion mutant in the Nossen accession with defects in floral development and growth. Most strikingly is the outgrowth of stems from the axillary bracts of the primary flower carrying secondary flowers. Therefore, we named this mutant flower-in-flower (fif ). However, the transposon insertion in the annotated gene is not the cause for the fif phenotype. By means of classical and genome sequencing-based mapping, the mutation responsible for the fif phenotype was found to be in the LEAFY gene. The mutation, a G-to-A exchange in the second exon of LEAFY, creates a novel lfy allele and results in a cysteine-to-tyrosine exchange in the α1-helix of LEAFY's DNA-binding domain. This exchange abolishes target DNA-binding, whereas subcellular localization and homomerization are not affected. To explain the strong fif phenotype against these molecular findings, several hypotheses are discussed. of 16intermediate between floral and vegetative shoots. The cloning of the corresponding genes revealed the existence of the master regulators required for the floral initiation process. To date, five regulatory master genes are known: LEAFY (LFY), APETALA1 (AP1), CAULIFLOWER (CAL), APETALA2 (AP2) and UNUSUAL FLORAL ORGANS (UFO) [3]. LFY and AP1 play a primary role in initiating the floral program, as the corresponding loss-of-function mutants do not generate shoots with floral characteristics and the ectopic expression of either gene induces precocious flower formation [9][10][11]. LFY, AP1 and CAL encode for transcription factors and are expressed predominantly in floral primordia [12][13][14].During plant vegetative growth, LFY expression increases in newly formed leaves until a certain threshold is reached [15]. LFY then induces the expression of AP1/CAL genes by activation of the AP1/CAL promoters. Through their mutual transcriptional up-regulation, LFY and AP1/CAL cooperate to cause the floral transition [16,17]. Once the floral meristem is established, the floral initiation gene functions govern its spatial patterning by inducing the expression of the floral homeotic ABC genes, such as AP2, AP3, Pistillata (PI) and AGAMOUS (AG). The ABC gene functions in turn control the identity of the stereotypically arranged Arabidopsis floral organs [18,19].In the course of our study of the influence of abiotic stress on flower symmetry, we searched for novel insertion mutants with defects in floral development or morphology in different Arabidopsis thaliana accessions. We focused on genes that had not yet been linked to flowering. A Ds transposon insertion mutant, which developed secon...

RNAi Suppression of LEAFY Gives Stable Floral Sterility, and Reduced Growth Rate and Leaf Size, in Field-Grown Poplars

“…We did not observe any major alterations in overall tree architecture or form between our RNAi trees and our control trees. Unsurprisingly, this is in contrast to findings in the annual plant Arabidopsis , where analysis of a novel lfy mutant showed very noticeable impacts on vegetative features, such as increased number of rosette leaves, additional stem-born branches, and longer stems related to delayed onset and structure of flowers [ 15 ]. Annual Arabidopsis plants normally grow several terminal floral structures along a main stem, while the lfy mutants of Arabidopsis have branches in these equivalent positions [ 15 ].…”

“…Unsurprisingly, this is in contrast to findings in the annual plant Arabidopsis , where analysis of a novel lfy mutant showed very noticeable impacts on vegetative features, such as increased number of rosette leaves, additional stem-born branches, and longer stems related to delayed onset and structure of flowers [ 15 ]. Annual Arabidopsis plants normally grow several terminal floral structures along a main stem, while the lfy mutants of Arabidopsis have branches in these equivalent positions [ 15 ]. By contrast, floral development in perennial poplar starts to form floral buds the growing season prior to floral bud flush, and these buds remain dormant over the winter [ 26 ].…”

“…There are very limited studies of the vegetative features of loss-of-function mutants of floral development genes, most studies are in herbaceous annuals, and none analyzed productivity effects in a randomized trial. For example, a novel lfy mutant in A. thaliana ecotype No-0 showed increased stem height and additional branches [ 15 ]. Similarly, tomato fa mutants (loss of FLORICAULA , tomato homology of LFY ) leads to shoots growing in place of flowers, giving plants a bushy appearance [ 7 ].…”

Three-Fluorophore FRET Enables the Analysis of Ternary Protein Association in Living Plant Cells

“…For transformations with multiple constructs, an OD 600 of 0.1 was set and mixed 1:1:1 with silencing inhibitor p19. Plants were watered and left at ambient conditions (24 °C) with the lid on top and imaged two days past transformation with an SP8 confocal laser scanning microscope (CLSM) (Leica Microsystems GmbH, Wetzlar, Germany) with LAS AF and SymPhoTime software (Picoquant GmbH, Berlin, Germany) using a 63×/1.20 water immersion objective [ 46 , 47 ]. Data were derived from measurements of the lower epidermis, avoiding guard cells and stomata, with at least two biological replicates, comprising in average 20 data points and 11 data points for mTRQ2—mRFP controls.…”