Anther dehiscence is a crucial event in plant reproduction, tightly regulated and dependent on the lignification of the anther endothecium. In this study, we investigated the rapid lignification process that ensures timely anther dehiscence in Arabidopsis. Our findings reveal that endothecium lignification can be divided into two distinct phases. During Phase I, lignin precursors are synthesized without polymerization, while Phase II involves simultaneous synthesis of lignin precursors and polymerization. The transcription factors MYB26, NST1/2, and ARF17 specifically regulate the pathway responsible for the synthesis and polymerization of lignin monomers in Phase II. MYB26-NST1/2 is the key regulatory pathway responsible for endothecium lignification, while ARF17 facilitates this process by interacting with MYB26. Interestingly, our results demonstrate that the lignification of the endothecium, which occurs within approximately 26 h, is much faster than that of the vascular tissue. These findings provide valuable insights into the regulation mechanism of rapid lignification in the endothecium, which enables timely anther dehiscence and successful pollen release during plant reproduction.

Proper anther dehiscence is essential for successful pollination and reproduction in angiosperms, and jasmonic acid (JA) is crucial for the process. However, the mechanisms underlying the tight regulation of JA biosynthesis during anther development remain largely unknown. Here, we demonstrate that the rice (Oryza sativa L.) ethylene-response factor-associated amphiphilic repression (EAR) motif-containing protein TEOSINTE BRANCHED1/CYCLOIDEA/PROLIFERATING CELL FACTORS (TCP) INTERACTOR CONTAINING EAR MOTIF PROTEIN1 (OsTIE1) tightly regulates JA biosynthesis by repressing TCP transcription factor OsTCP1/PCF5 during anther development. The loss of OsTIE1 function in Ostie1 mutants causes male sterility. The Ostie1 mutants display inviable pollen, early stamen filament elongation, and precocious anther dehiscence. In addition, JA biosynthesis is activated earlier and JA abundance is precociously increased in Ostie1 anthers. OsTIE1 is expressed during anther development, and OsTIE1 is localized in nuclei and has transcriptional repression activity. OsTIE1 directly interacts with OsTCP1, and overexpression of OsTCP1 caused early anther dehiscence resembling that of Ostie1. JA biosynthesis genes including rice LIPOXYGENASE are regulated by the OsTIE1-OsTCP1 complex. Our findings reveal that the OsTIE1-OsTCP1 module plays a critical role in anther development by finely tuning JA biosynthesis and provide a foundation for the generation of male sterile plants for hybrid seed production.

Male sterility is a highly attractive agronomic trait as it effectively prevents self-fertilization and facilitates the production of high-quality hybrid seeds in plants. Timely release of mature pollen following anther dehiscence is essential for stamen development in flowering plants. Although several theories have been proposed regarding this, the specific mechanism of anther development in eggplant remains elusive. In this study, we selected an R2R3-MYB transcription factor gene, SmMYB108, that encodes a protein localized primarily in the nucleus by comparing the transcriptomics of different floral bud developmental stages of the eggplant fertile line, F142. Quantitative reverse transcription polymerase chain reaction revealed that SmMYB108 was preferentially expressed in flowers, and its expression increased significantly on the day of flowering. Overexpression of SmMYB108 in tobacco caused anther dehiscence. In addition, we found that SmMYB108 primarily functions as a transcriptional activator via C-terminal activation (amino acid 262-317). Yeast one-hybrid and dual-luciferase reporter assays revealed that genes (SmMYB21, SmARF6, and SmARF8) related to anther development targeted the SmMYB108 promoter. Overall, our results provide insights into the molecular mechanisms involved in the regulation of anther development by SmMYB108.

A novel male-sterility trait was identified in a radish (Raphanus sativus L.) population. Although the size of male-sterile anthers was comparable to that of normal flowers, no pollen grain was observed during anther dehiscence. However, dissection of male-sterile anthers revealed an abundance of normal pollen grains. Analysis of segregating populations showed that a single recessive locus, designated RsMs1, conferred male sterility. Based on two radish draft genome sequences, molecular markers were developed to delimit the genomic region harboring the RsMs1. The region was narrowed down to approximately 24 kb after analyzing recombinants selected from 7511 individuals of a segregating population. Sequencing of the delimited region yielded six putative genes including four genes expressed in the floral tissue, and one gene with significant differential expression between male-fertile and male-sterile individuals of a segregating population. This differentially expressed gene was orthologous to the Arabidopsis MYB26 gene, which played a critical role in anther dehiscence. Excluding a synonymous single nucleotide polymorphism in exon3, no polymorphism involving coding and putative promoter regions was detected between alleles. A 955-bp insertion was identified 7.5 kb upstream of the recessive allele. Highly conserved motifs among four Brassicaceae species were identified around this insertion site, suggesting the presence of putative enhancer sequences. A functional marker was developed for genotyping of the RsMs1 based on the 955-bp insertion. A total of 120 PI accessions were analyzed using this marker, and 11 accessions were shown to carry the recessive rsms1 allele.
UNASSIGNED: The online version contains supplementary material available at 10.1007/s11032-021-01254-9.

Anther dehiscence is an important process to release pollen and then is a critical event in pollination. In the wheat photo-thermo-sensitive genic male sterility (PTGMS) line, pollen cannot release from anther since the anther cannot dehisce during anther dehiscence stage in a sterile condition. In this study, we carried out RNA-sequencing to analyze the transcriptome of one wheat PTGMS line BS366 during anther dehiscence under fertile and sterile conditions to explore the mechanism. We identified 6306 differentially expressed genes (DEGs). Weighted gene co-expression network analysis (WGCNA) and KEGG analysis showed that DEGs were mainly related to \"hormone signal transduction pathway\" and \"starch and sucrose metabolism\". We identified 35 and 23 DEGs related hormone signal transduction and sucrose metabolism, respectively. Compared with conventional wheat Jing411, there were some changes in the contents of hormones, including JA, IAA, BR, ABA and GA3, and sucrose, during three anther dehiscence stages in the sterile condition in BS366. We performed qRT-PCR to verify the expression levels of some critical DEGs of the hormone signaling pathway and the starch and sucrose metabolism pathway. The results showed disparate expression patterns of the critical DEGs of the hormone signaling pathway and the starch and sucrose metabolism pathway in different conditions, suggesting these genes may be involved in the regulation of the anther dehiscence in BS366. Finally, we conducted a hypothesis model to reveal the regulation pathway of hormones and sucrose on anther dehiscence. The information provided new clues to the molecular mechanisms of anther dehiscence in wheat and improved wheat hybrid breeding.

Glycoside hydrolase family 9 (GH9) is a key member of the hydrolase family in the process of cellulose synthesis and hydrolysis, playing important roles in plant growth and development. In this study, we investigated the phenotypic characteristics and gene expression involved in pollen fertility conversion and anther dehiscence from a genomewide level. In total, 74 wheat GH9 genes (TaGH9s) were identified, which were classified into Class A, Class B and Class C and unevenly distributed on chromosomes. We also investigated the gene duplication and reveled that fragments and tandem repeats contributed to the amplification of TaGH9s. TaGH9s had abundant hormone-responsive elements and light-responsive elements, involving JA-ABA crosstalk to regulate anther development. Ten TaGH9s, which highly expressed stamen tissue, were selected to further validate their function in pollen fertility conversion and anther dehiscence. Based on the cell phenotype and the results of the scanning electron microscope at the anther dehiscence period, we found that seven TaGH9s may target miRNAs, including some known miRNAs (miR164 and miR398), regulate the level of cellulose by light and phytohormone and play important roles in pollen fertility and anther dehiscence. Finally, we proposed a hypothesis model to reveal the regulation pathway of TaGH9 on fertility conversion and anther dehiscence. Our study provides valuable insights into the GH9 family in explaining the male sterility mechanism of the wheat photo-thermo-sensitive genetic male sterile (PTGMS) line and generates useful male sterile resources for improving wheat hybrid breeding.

In plants, the key enzyme in ethylene biosynthesis is 1-aminocyclopropane-1 carboxylic acid (ACC) synthase (ACS), which catalyzes S-adenosyl-L-methionine (SAM) to ACC, the precursor of ethylene. Ethylene binds to its receptors, such as ethylene response 1 (ETR1), to switch on ethylene signal transduction. To understand the function of ACS and ETR1 in orchids, Oncidium ACC synthase 12 (OnACS12) and Oncidium ETR1 (OnETR1) from Oncidium Gower Ramsey were functionally analyzed in Arabidopsis. 35S::OnACS12 caused late flowering and anther indehiscence phenotypes due to its effect on GA-DELLA signaling pathways. 35S::OnACS12 repressed GA biosynthesis genes (CPS, KS, and GA3ox1), which caused the upregulation of DELLA [GA-INSENSITIVE (GAI), RGA-LIKE1 (RGL1), and RGL2] expression. The increase in DELLAs not only suppressed LEAFY (LFY) expression and caused late flowering but also repressed the jasmonic acid (JA) biosynthesis gene DAD1 and caused anther indehiscence by downregulating the endothecium-thickening-related genes MYB26, NST1, and NST2. The ectopic expression of an OnETR1 dominant-negative mutation (OnETR1-C65Y) caused both ethylene and JA insensitivity in Arabidopsis. 35S::OnETR1-C65Y delayed flower/leaf senescence by suppressing downstream genes in ethylene signaling, including EDF1-4 and ERF1, and in JA signaling, including MYC2 and WRKY33. JA signaling repression also resulted in indehiscent anthers via the downregulation of MYB26, NST1, NST2, and MYB85. These results not only provide new insight into the functions of ACS and ETR1 orthologs but also uncover their functional interactions with other hormone signaling pathways, such as GA-DELLA and JA, in plants.

Lily (Lilium spp.) is a widely cultivated horticultural crop that has high ornamental and commercial value but also the serious problem of pollen pollution. However, mechanisms of anther dehiscence in lily remain largely unknown. In this study, the morphological characteristics of the stomium zone (SZ) from different developmental stages of \'Siberia\' lily anthers were investigated. In addition, transcriptomic and metabolomic data were analyzed to identify the differentially expressed genes (DEGs) and secondary metabolites involved in stomium degeneration. According to morphological observations, SZ lysis occurred when flower buds were 6-8 cm in length and was completed in 9 cm. Transcriptomic analysis identified the genes involved in SZ degeneration, including those associated with hormone signal transduction, cell structure, reactive oxygen species (ROS), and transcription factors. A weighted co-expression network showed strong correlations between transcription factors. In addition, TUNEL (TdT-mediated dUTP nick-end labeling) assays showed that programmed cell death was important during anther SZ degeneration. Jasmonates might also have key roles in anther dehiscence by affecting the expression of the genes involved in pectin lysis, water transport, and cysteine protease. Collectively, the results of this study improve our understanding of anther dehiscence in lily and provide a data platform from which the molecular mechanisms of SZ degeneration can be revealed.

Phospholipase D (PLD) and its hydrolysis product phosphatidic acid play an important role in the regulation of several cellular processes, including root growth, pollen tube elongation, and microtubule reorganization. Here, we systematically identified and analyzed the membership, characterization, and evolutionary relationship of PLDs in five species of cotton. The results of the transcriptomic analysis suggested that the evaluated PLD genes showed high expression levels in anther tissue and during the fiber initiation and elongation periods. Quantitative real-time polymerase chain reaction showed differential expression of GhPLD genes in the anthers of photoperiod sensitive male sterility mutant 5 (psm5). Previous research on multiple stable quantitative trait loci also suggests the role of PLD genes in the fiber development. Further analyses showed that GhPLD2 protein is localized to the plasma membrane. The virus-induced gene silencing of GhPLD2 in cotton seedlings repressed its expression by 40-70%, which led to a reduction in reactive oxygen species (ROS) levels, 22% anther indehiscence, and disrupted fiber initiation and elongation. Thus, we inferred that GhPLD2 may promote ROS production, which, in turn, may regulate anther dehiscence and fiber development.

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.