In flowering plants, proper development of male generative organs is required for successful sexual reproduction. Stamen primordia arise in the third whorl of floral organs and subsequently differentiate into filaments and anthers. The early phase of stamen development, in which meiosis occurs, is followed by a late developmental phase, which consists of filament elongation coordinated with pollen maturation, anther dehiscence and finally viable pollen grain release. Stamen development and function are modulated by phytohormones, with a key role of gibberellins (GAs) and jasmonates (JAs). Long-term, extensive investigations, mainly involving GA/JA-deficient and GA/JA-response mutants, have led to a better understanding of the hormone-dependent molecular mechanisms of stamen development. In several species, the principal functions of GAs are to stimulate filament elongation through increased cell elongation and to promote anther locule opening. In the GA-dependent regulation of early stamen development, both the tapetum and developing pollen were identified as major targets. JAs mainly control the late stages of stamen development, such as filament elongation, viable pollen formation and anther dehiscence. A hierarchical relationship between GAs and JAs was recognized mainly in the control of late stamen development. By repressing DELLA proteins, GAs modulate the transcriptional activity of JA biosynthesis genes to promote JA production. A high level of JAs induces a complex of transcription factors crucial for normal stamen development.

No abstract

Precise control of generative organ development is of great importance for the productivity of crop plants, including legumes. Gibberellins (GAs) play a key role in the regulation of flowering, and fruit setting and development. The major repressors of GA signaling are DELLA proteins. In this paper, the full-length cDNA of LlDELLA1 gene in yellow lupine (Lupinus luteus L.) was identified. Nuclear-located LlDELLA1 was clustered in a second phylogenetic group. Further analyses revealed the presence of all conserved motifs and domains required for the GA-dependent interaction with Gibberellin Insensitive Dwarf1 (GID1) receptor, and involved in the repression function of LlDELLA1. Studies on expression profiles have shown that fluctuating LlDELLA1 transcript level favors proper flower and pod development. Accumulation of LlDELLA1 mRNA slightly decreases from the flower bud stage to anther opening (dehiscence), while there is rapid increase during pollination, fertilization, as well as pod setting and early development. LlDELLA1 expression is downregulated during late pod development. The linkage of LlDELLA1 activity with cellular and tissue localization of gibberellic acid (GA3) offers a broader insight into the functioning of the GA pathway, dependent on the organ and developmental stage. Our analyses provide information that may be valuable in improving the agronomic properties of yellow lupine.

Background Anther dehiscence resulting in the release of pollen grains is tightly regulated in a spatiotemporal manner by various factors. In yellow lupine (Lupinus luteus L.), a species that shows cleistogamy, the anthers split before the flowers open, but the course and regulation of this process are unknown. The specific control of anther development takes place via hormonal pathways, the wide action of which ensures reproductive success. In our previous research concerning flower and early pod development in yellow lupine, we showed that the lowest transcript level of LlDELLA1, a main repressor of gibberellin (GA) signalling, occurs approximately at the time of anther opening; therefore, the main purpose of this study was to precisely investigate the gibberellic acid (GA3)-dependent regulation of the anther dehiscence in this species. Results In this paper, we showed the specific changes in the yellow lupine anther structure during dehiscence, including secondary thickening in the endothecium by lignocellulosic deposition, enzymatic cell wall breakdown at the septum/stomium and cell degeneration via programmed cell death (PCD), and identified several genes widely associated with this process. The expression profile of genes varied over time, with the most intense mRNA accumulation in the phases prior to or at the time of anther opening. The transcriptional activity also revealed that these genes are highly coexpressed and regulated in a GA-dependent manner. The cellular and tissue localization of GA3 showed that these molecules are present before anther opening, mainly in septum cells, near the vascular bundle and in the endothecium, and that they are subsequently undetectable. GA3 localization strongly correlates with the transcriptional activity of genes related to GA biosynthesis and deactivation. The results also suggest that GA3 controls LlGAMYB expression via an LlMIR159-dependent pathway. Conclusions The presented results show a clear contribution of GA3 in the control of the extensive anther dehiscence process in yellow lupine. Understanding the processes underlying pollen release at the hormonal and molecular levels is a significant aspect of controlling fertility in this economically important legume crop species and is of increasing interest to breeders.

Aktywność strefy odcinania (AZ, ang. abscission zone) warunkuje separację organów od rośliny macierzystej. U Lupinus luteus AZ kwiatów powstaje u podstawy szypułek tych organów. Zmiany na poziomie komórkowym są skorelowane ze zmieniająca się ekspresją BLADE-ON-PETIOLE (LlBOP). Poziom mRNA tego genu regulowany jest także przez hormonalne stymulatory odcinania kwiatów — etylen (ET) i kwas abscysynowy (ABA) — co wskazuje, że LlBOP jest zaangażowany nie tylko w powstawanie AZ, ale także w późniejsze etapy jej funkcjonowania. Kwas abscysynowy wpływając na akumulację transkryptów genów kodujących enzymy biosyntezy etylenu ET (syntazę i oksydazę kwasu 1-aminocyklopropano-1-karboksylowego (ACC) i jednocześnie powodując wzrost poziomu prekursora tego fitohormonu w AZ, pośrednio reguluje czas odcinania kwiatów L. luteus.