TWISTED DWARF1 regulates Arabidopsis stamen development by differential activation of ABCB-mediated auxin transport

Despite clear evidence that a local accumulation of auxin is likewise critical for male fertility, much less is known about the components that regulate auxin-controlled stamen development.In this study, we analyzed physiological and morphological parameters in mutants of key players of ABCB-mediated auxin transport and spatially and temporally dissected their expression on the protein level as well as auxin fluxes in the Arabidopsis stamens. Our analyses revealed that the FKBP42, TWISTED DWARF1 (TWD1), promotes stamen elongation and, to a lesser extent, anther dehiscence, as well as pollen maturation and thus is required for seed development. Most of the described developmental defects in twd1 are shared with the abcb1 abcb19 mutant, which can be attributed to the fact that TWD1 - as a described ABCB chaperon - is a positive regulator of ABCB1 and ABCB19-mediated auxin transport. However, reduced stamen number was dependent on TWD1 but not on investigated ABCBs, suggesting additional actors down-stream of TWD1. We predict an overall housekeeping function for ABCB1 during earlier stages, while ABCB19 seems to be responsible for the key event of rapid elongation at later stages of stamen development. Our data indicate that TWD1 controls stamen development by differential activation of ABCB-mediated auxin transport in the stamen.HighlightBy using a mix of phenotypical and imaging analyses, we here identify and functionally characterize a new master regulator of flower development.

IS THE FLOWER OF PULASAN (NEPHELIUM RAMBOUTAN-AKE) A PROTOGYNY OR PROTANDRY?

Pulasan is an androdioecious plant that has both male and hermaphrodite flowers on separate plants. The objectives of this study were to obtain data about the anatomical structure of pulasan flower and to investigate whether the pistil and the stamens of pulasan flower reach maturity at different times. The anatomical observation was done on compound flowers taken from three male trees and three hermaphrodite trees. Two compound flowers that still in buds, about to bloom and fully bloom were picked from each tree. Flowers were observed in a cross and longitudinal section. The results showed that the sepals of pulasan flower comprised of the uniseriate epidermis and multilayered polyhedral parenchymal cells. Stamen development started from the anther followed by the formation of the filament. The pollen of hermaphrodite pulasan flowers reached maturation earlier than the pistil. The pistil development started from the expansion of meristem cells in the center of the flower and ends with the warp of the stigma.

TWISTED DWARF1 regulates Arabidopsis stamen development by differential activation of ABCB-mediated auxin transport

Despite clear evidence that a local accumulation of auxin is likewise critical for floral organ initiation than for vegetative tissues, much less is known about the molecular key players that regulate auxin-controlled flower development. Here, by an analysis of physiological and morphological parameters and by a spatial and temporal dissection of auxin fluxes and expression of key players of ABCB-mediated auxin transport in the Arabidopsis flower, we demonstrate a crucial role for the FKBP42, TWISTED DWARF1 (TWD1), in the regulation of flower development. Our analyses revealed that TWD1 promotes flower shape and number, stamen elongation, pollen maturation, nectary functionality and seed development. Most of the described developmental defects in twd1 are shared with the abcb1 abcb19 mutant, which can be attributed to the fact that TWD1 as a described ABCB chaperon is a positive regulator of ABCB1 and ABCB19-mediated auxin transport. We predict an overall housekeeping function for ABCB1 during earlier stages, while ABCB19 seems to be responsible for the key event of rapid elongation at later stages of stamen development. Our data indicate that TWD1 controls flower development by differential activation of ABCB-mediated auxin transport.

Isolation and Characterization of APETALA3 Orthologs and Promoters from the Distylous Fagopyrum esculentum

Common buckwheat (Fagopyrum esculentum) produces distylous flowers with undifferentiated petaloid tepals, which makes it obviously different from flowers of model species. In model species Arabidopsis, APETALA3 (AP3) is expressed in petal and stamen and specifies petal and stamen identities during flower development. Combining with our previous studies, we found that small-scale gene duplication (GD) event and alternative splicing (AS) of common buckwheat AP3 orthologs resulted in FaesAP3_1, FaesAP3_2 and FaesAP3_2a. FaesAP3_2 and FaesAP3_2a were mainly expressed in the stamen of thrum and pin flower. Promoters functional analysis suggested that intense GUS staining was observed in the whole stamen in pFaesAP3_2::GUS transgenic Arabidopsis, while intense GUS staining was observed only in the filament of stamen in pFaesAP3_1::GUS transgenic Arabidopsis. These suggested that FaesAP3_1 and FaesAP3_2 had overlapping functions in specifying stamen filament identity and work together to determine normal stamen development. Additionally, FaesAP3_2 and FaesAP3_2a owned the similar ability to rescue stamen development of Arabidopsis ap3-3 mutant, although AS resulted in a frameshift mutation and consequent omission of the complete PI-derived motif and euAP3 motif of FaesAP3_2a. These suggested that the MIK region of AP3-like proteins was crucial for determining stamen identity, while the function of AP3-like proteins in specifying petal identity was gradually obtained after AP3 Orthologs acquiring a novel C-terminal euAP3 motif during the evolution of core eudicots. Our results also provide a clue to understanding the early evolution of the functional specificity of euAP3-type proteins involving in floral organ development in core eudicots, and also suggested that FaesAP3_2 holds the potential application for biotechnical engineering to develop a sterile male line of F. esculentum.

Ectopic Expressions of the GhLETM1 Gene Reveal Sensitive Dose Effects on Precise Stamen Development and Male Fertility in Cotton

The homologous leucine zipper/EF-hand-containing transmembranes (LETMs) are highly conserved across a broad range of eukaryotic organisms. The LETM functional characteristics involved in biological process have been identified primarily in animals, but little is known about the LETM biological function mode in plants. Based on the results of the current investigation, the GhLETM1 gene crucially affects filament elongation and anther dehiscence of the stamen in cotton. Both excessive and lower expression of the GhLETM1 gene lead to defective stamen development, resulting in shortened filaments and indehiscent anthers with pollen abortion. The results also showed that the phenotype of the shortened filaments was negatively correlated with anther defects in the seesaw model under the ectopic expression of GhLETM1. Moreover, our results notably indicated that the gene requires accurate expression and exhibits a sensitive dose effect for its proper function. This report has important fundamental and practical significance in crop science, and has crucial prospects for genetic engineering of new cytoplasmic male sterility lines and breeding of crop hybrid varieties.