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Heat stress during flowering has differential impact on male and female reproductive organ viability leading to yield losses in field crops. Unlike flooded rice, dryland cereals such as sorghum, pearl millet and wheat have optimised their flower opening during cooler early morning or late evening hours to lower heat stress damage during flowering. Although previous studies have concluded that pollen viability determines seed set under heat stress, recent findings have revealed pearl millet and sorghum pistils to be equally sensitive to heat stress. Integrating flower opening time during cooler hours with increased pollen and pistil viability will overcome heat stress-induced damage during flowering under current and future hotter climatic conditions.

Main conclusionExtensive histology of pistillate flowers revealed two pollen tube arresting sites (the style-joining and micropyle) within the pistil of Quercus acutissima during the postpollination–prezygotic stage, which reflects a unique female and male gametophyte recognition/selection mechanism.Sexual reproduction is among the most delicate and essential stages in plant life cycles and involves a series of precise interactions between pistils and male gametophytes. Quercus is a woody genus that dominates Northern Hemisphere forests and is notorious for interspecific hybridization, but its sexual reproduction is poorly understood, especially its pollen tube (PT) growth dynamics within pistils. This study used microtome techniques and scanning electron microscopy to observe the postpollination–prezygotic process in the biennially fruiting oak Quercus acutissima. Many pollen grains germinated at anthesis instantly, and PTs penetrated stigmatic surfaces and elongated through the stylar transmitting tissue, then arrested at style-joining for about 12–13 months. Few PTs resumed growth along the compitum in the upper ovarian locule wall in the subsequent April, concurrent with the rapid growth of rudimentary ovules. PTs arrived in the micropyle, and upper septum during megaspore mother cell meiosis, then arrested again for 7–10 days waiting for the embryo sac maturation. Fertilization occurred one week later. Our study shows a clear female dominant crosstalk growth pattern between PT and the ovule. The intermittent PT growth might reflect a unique male gametophyte recognition/selection mechanism to avoid self-pollination and enhance PT competition while increasing interspecific hybridization.

OsMAIL1 encodes for a rice protein of the Plant Mobile Domain (PMD) family and is strongly upregulated during floral induction in response to the presence of the florigens Heading date 3a (Hd3a) and RICE FLOWERING LOCUS T1 (RFT1). Although OsMAIL1 expression depends on the florigens, osmail1 null mutants do not show delay in flowering time, rather OsMAIL1 participates in ensuring successful reproduction. Indeed, when day temperatures reach 35 °C (7 °C higher than standard greenhouse conditions), osmail1 mutants show increased sterility due to abnormal pistil development with about half of the plants developing three styles topped by stigmas. OsMAIL1 expression correlates with that of carpel identity genes and RNA-seq of osmail1-1 mutant compared to the wt during inflorescence development showed that OsMAIL1 is required to activate carpel identity genes expression when floral meristems are about to be initiated. OsMAIL1 is a newly characterized rice gene that specifically controls carpel development under heat stress, ensuring plant female fertility in these conditions. Key message OsMAIL1 is a Plant Mobile Domain protein that controls correct pistil development by preventing misexpression of floral homeotic genes when day temperatures reach 35°C during floral transition. In such conditions, osmail1 mutants develop abnormal three-styled pistils that can’t be usually fertilized.

Background Papaya exhibits three sex types: female (XX), male (XY), and hermaphrodite (XY h ), making it an unusual trioecious model for studying sex determination. A critical aspect of papaya sex determination is the pistil abortion in male flowers. However, the regulatory networks that control the development of pistils and stamens in papaya remain incompletely understood. Results In this study, we identified three organ-specific clusters involved in papaya pistils and stamens development. We found that pistil development is primarily characterized by the significant expression of auxin-related genes, while the pistil abortion genes in males is mainly associated with cytokinin, gibberellin, and auxin pathways. Additionally, we constructed expression regulatory networks for the development of female pistils, aborted pistils and stamens in male flowers, revealing key regulatory genes and signaling pathways involved in papaya organ development. Furthermore, we systematically identified 65 members of the MADS-box gene family and 10 ABCDE subfamily MADS-box genes in papaya. By constructing a phylogenetic tree of the ABCDE subfamily, we uncovered gene contraction and expansion in papaya, providing an improved understanding of the developmental mechanisms and evolutionary history of papaya floral organs. Conclusions These findings provide a robust framework for identifying candidate sex-determining genes and constructing the sex determination regulatory network in papaya, providing insights and genomic resources for papaya breeding.

• Distyly is an intriguing floral adaptation that increases pollen transfer precision and restricts inbreeding. It has been a model system in evolutionary biology since Darwin. Although the S-locus determines the long- and short-styled morphs, the genes were unknown in Turnera. We have now identified these genes. • We used deletion mapping to identify, and then sequence, BAC clones and genome scaffolds to construct S/s haplotypes. We investigated candidate gene expression, hemizygosity, and used mutants, to explore gene function. • The s-haplotype possessed 21 genes collinear with a region of chromosome 7 of grape. The S-haplotype possessed three additional genes and two inversions. TsSPH1 was expressed in filaments and anthers, TsYUC6 in anthers and TsBAHD in pistils. Long-homostyle mutants did not possess TsBAHD and a short-homostyle mutant did not express TsSPH1. • Three hemizygous genes appear to determine S-morph characteristics in T. subulata. Hemizygosity is common to all distylous species investigated, yet the genes differ. The pistil candidate gene, TsBAHD, differs from that of Primula, but both may inactivate brassinosteroids causing short styles. TsYUC6 is involved in auxin synthesis and likely determines pollen characteristics. TsSPH1 is likely involved in filament elongation. We propose an incompatibility mechanism involving TsYUC6 and TsBAHD.

Multi-pistil trait in wheat is of great potential value in plant development research and crop breeding. Our previous studies identified the Pis1 locus that causes three pistils in wheat by genetic mapping using multiple DNA marker systems. However, there are still 26 candidate genes on the locus, and the causal gene remains to be found. In this study, we aimed to approach the molecular mechanism of multi-pistil formation. Comparative RNA sequencing (RNA-Seq) during the pistil formation was undertaken in four wheat lines: a three-pistil mutant TP, a single-pistil TILLING mutant of TP (SP), a three-pistil near-isogenic line CM28TP with the background of cultivar Chunmai 28 (CM28), and CM28. Electron microscopic analysis specified probable developmental stages of young spikes for the three-pistil formation. mRNA sequencing in the young spikes of the four lines represented 253 down-regulated genes and 98 up-regulated genes in both three-pistil lines, which included six potential genes for ovary development. Weighted gene co-expression analysis represented three-pistil trait-associated transcription factor-like genes, among which one hub gene, ARF5 , was the most highlighted. ARF5 is on the Pis1 locus and an orthologue of MONOPTEROS which mediates tissue development in Arabidopsis . qRT-PCR validation implies that the deficiency of ARF5 underlies the three-pistil formation in wheat.

Flowering plants have evolved numerous intraspecific and interspecific prezygotic reproductive barriers to prevent production of unfavourable offspring 1 . Within a species, self-incompatibility (SI) is a widely utilized mechanism that rejects self-pollen 2 , 3 to avoid inbreeding depression. Interspecific barriers restrain breeding between species and often follow the SI × self-compatible (SC) rule, that is, interspecific pollen is unilaterally incompatible (UI) on SI pistils but unilaterally compatible (UC) on SC pistils 1 , 4 – 6 . The molecular mechanisms underlying SI, UI, SC and UC and their interconnections in the Brassicaceae remain unclear. Here we demonstrate that the SI pollen determinant S -locus cysteine-rich protein/ S -locus protein 11 (SCR/SP11) 2 , 3 or a signal from UI pollen binds to the SI female determinant S -locus receptor kinase (SRK) 2 , 3 , recruits FERONIA (FER) 7 – 9 and activates FER-mediated reactive oxygen species production in SI stigmas 10 , 11 to reject incompatible pollen. For compatible responses, diverged pollen coat protein B-class 12 – 14 from SC and UC pollen differentially trigger nitric oxide, nitrosate FER to suppress reactive oxygen species in SC stigmas to facilitate pollen growth in an intraspecies-preferential manner, maintaining species integrity. Our results show that SRK and FER integrate mechanisms underlying intraspecific and interspecific barriers and offer paths to achieve distant breeding in Brassicaceae crops. A signalling mechanism ensuring intraspecies and interspecies reproductive barriers in flowering plants is uncovered.

Background Long non-coding RNAs (lncRNAs) are transcripts more than 200 bp in length do not encode proteins. Up to the present, it has been reported that lncRNAs play an essential role in developmental processes through their regulatory functions. However, their characteristics, expression inheritance patterns, and functions in Prunus mume are quite unidentified. Results In this present study, we exposed the specific characters of pistil development process between single pistil cv ‘Qingjia No.2’ (QJN2) and multiple pistils cv ‘Da Yu’ (DY). We found that early October is the key stage for pistil differentiation. The similarity epidermis was observed between two types of pistil. We also further investigated a complete pistil development lncRNA profiles through RNA-seq in Prunus mume . 2572 unique lncRNAs and 24,648 genes mapped to Prunus mume genome, furthermore, 591 novel lncRNAs were predicted. Both unique lncRNAs and novel lncRNAs are shorter in length than the mRNAs, and the overall expression level of lncRNAs was lower than mRNAs in Prunus mume . 186 known lncRNAs, 1638 genes and 89 novel lncRNAs were identified as significant differential expressed in QJN2 compared with DY. We predicted 421 target genes of differentially expressed known lncRNAs (DEKLs) and 254 target genes of differentially expressed novel lncRNAs (DENLs). 153 miRNAs were predicted interacted with 100 DEKLs while 112 miRNAs were predicted interacted with 55 DENLs. Further analysis of the DEKLs showed that the lncRNA of XR_514690.2 down-regulated its target ppe-miR172d, and up-regulated AP2 , respectively. Meanwhile, the other lncRNA of TCONS_00032517 induced cytokinin negative regulator gene A-ARR expression via repressing its target miRNA ppe-miR160a/b in DY. At the same time we found that the A P2 expression was significantly up-regulated by zeatin (ZT) treatment in flower buds. Our experiments suggest that the two lncRNAs of XR_514690.2 and TCONS_00032517 might contribute the formation of multiple pistils in Prunus mume . Conclusion This study shows the first characterization of lncRNAs involved in pistil development and provides new indications to elucidate how lncRNAs and their targets play role in pistil differentiation and flower development in Prunus mume .

• In self-incompatible Petunia species, the pistil S-RNase acts as cytotoxin to inhibit self-pollination but is polyubiquitinated by the pollen-specific nonself S-locus F-box (SLF) proteins and subsequently degraded by the ubiquitin-proteasome system (UPS), allowing cross-pollination. However, it remains unclear how S-RNase is restricted by the UPS. • Using biochemical analyses, we first show that Petunia hybrida S₃-RNase is largely ubiquitinated by K48-linked polyubiquitin chains at three regions, R I, R II and R III. R I is ubiquitinated in unpollinated, self-pollinated and cross-pollinated pistils, indicating its occurrence before PhS₃-RNase uptake into pollen tubes, whereas R II and R III are exclusively ubiquitinated in cross-pollinated pistils. • Transgenic analyses showed that removal of R II ubiquitination resulted in significantly reduced seed sets from cross-pollination and that of R I and R III to a lesser extent, indicating their increased cytotoxicity. Consistent with this, the mutated R II of PhS₃-RNase resulted in a marked reduction of its degradation, whereas that of R I and R III resulted in less reduction. • Taken together, we demonstrate that PhS₃-RNase R II functions as a major ubiquitination region for its destruction and R I and R III as minor ones, revealing that its cytotoxicity is primarily restricted by a stepwise UPS mechanism for cross-pollination in P. hybrida.

Successful plant reproduction and fruit formation depend on adequate pollen and pistil development, and pollen–pistil interactions. In Nicotiana tabacum, pollen tubes grow through the intercellular spaces of pistil-specialized tissues, stigmatic secretory zone, and stylar transmitting tissue (STT). These intercellular spaces are supposed to be formed by the modulation of cell wall pectin esterification. Previously we have identified a gene preferentially expressed in pistils encoding a putative pectin acetylesterase (PAE), named NtPAE1. Here, we characterized the NtPAE1 gene and performed genome-wide and phylogenetic analyses of PAEs. We identified 30 PAE sequences in the N. tabacum genome, distributed in four clades. The expression of NtPAE1 was assessed by RT-qPCR and in situ hybridization. We confirmed NtPAE1 preferential expression in stigmas/styles and ovaries and demonstrated its high expression in the STT. Structural predictions and comparisons between NtPAE1 and functional enzymes validated its identity as a PAE. Transgenic plants were produced, overexpressing and silencing the NtPAE1 gene. Overexpressed plants displayed smaller flowers while silencing plants exhibited collapsed pollen grains, which hardly germinate. NtPAE1 silencing plants do not produce fruits, due to impaired pollen tube growth in their STTs. Thus, NtPAE1 is an essential enzyme regulating pectin modifications in flowers and, ultimately, in plant reproduction.