BACKGROUND: In Angiosperms, the continuation of plant species is intricately dependent on the funiculus multifaceted role in nutrient transport, mechanical support, and dehiscence of seeds. SEEDSTICK (STK) is a MADS-box transcription factor involved in seed size and abscission, and one of the few genes identified as affecting funiculus growth. Given the importance of the funiculus to a correct seed development, allied with previous phenotypic observations of stk mutants, we performed a transcriptomic analysis of stk funiculi from floral stage 17, using RNA-sequencing, to infer on the deregulated networks of genes.
RESULTS: The generated dataset of differentially expressed genes was enriched with cell wall biogenesis, cell cycle, sugar metabolism and transport terms, all in accordance with stk phenotype observed in funiculi from floral stage 17. We selected eight differentially expressed genes for transcriptome validation using qPCR and/or promoter reporter lines. Those genes were involved with abscission, seed development or novel functions in stk funiculus, such as hormones/secondary metabolites transport.
CONCLUSIONS: Overall, the analysis performed in this study allowed delving into the STK-network established in Arabidopsis funiculus, fulfilling a literature gap. Simultaneously, our findings reinforced the reliability of the transcriptome, making it a valuable resource for candidate genes selection for functional genetic studies in the funiculus. This will enhance our understanding on the regulatory network controlled by STK, on the role of the funiculus and how seed development may be affected by them.

Abscission is the shedding of plant organs in response to developmental and environmental cues. Abscission involves cell separation between two neighboring cell types, residuum cells (RECs) and secession cells (SECs) in the floral abscission zone (AZ) in Arabidopsis thaliana. However, the regulatory mechanisms behind the spatial determination that governs cell separation are largely unknown. The class I KNOTTED-like homeobox (KNOX) transcription factor BREVIPEDICELLUS (BP) negatively regulates AZ cell size and number in Arabidopsis. To identify new players participating in abscission, we performed a genetic screen by activation tagging a weak complementation line of bp-3. We identified the mutant ebp1 (enhancer of BP1) displaying delayed floral organ abscission. The ebp1 mutant showed a concaved surface in SECs and abnormally stacked cells on the top of RECs, in contrast to the precisely separated surface in the wild-type. Molecular and histological analyses revealed that the transcriptional programming during cell differentiation in the AZ is compromised in ebp1. The SECs of ebp1 have acquired REC-like properties, including cuticle formation and superoxide production. We show that SEPARATION AFFECTING RNA-BINDING PROTEIN1 (SARP1) is upregulated in ebp1 and plays a role in the establishment of the cell separation layer during floral organ abscission in Arabidopsis.

Cytokinetic abscission marks the final stage of cell division, during which the daughter cells physically separate through the generation of new barriers, such as the plasma membrane or cell wall. While the contractile ring plays a central role during cytokinesis in bacteria, fungi and animal cells, the process diverges in Apicomplexa. In Toxoplasma gondii, two daughter cells are formed within the mother cell by endodyogeny. The mechanism by which the progeny cells acquire their plasma membrane during the disassembly of the mother cell, allowing daughter cells to emerge, remains unknown. Here we identify and characterize five T. gondii proteins, including three protein phosphatase 2A subunits, which exhibit a distinct and dynamic localization pattern during parasite division. Individual downregulation of these proteins prevents the accumulation of plasma membrane at the division plane, preventing the completion of cellular abscission. Remarkably, the absence of cytokinetic abscission does not hinder the completion of subsequent division cycles. The resulting progeny are able to egress from the infected cells but fail to glide and invade, except in cases of conjoined twin parasites.

Detecting changes in the phenological responses of herbaceous species as a function of predicted climate change is important for forecasting future scenarios for the functioning of dry tropical forests, especially when predicting an increase in the frequency and intensity of extreme droughts. Because of the sensitivity of plants to water availability, our study hypothesizes that if years become drier or wetter, herbaceous plants will synchronously change the onset, duration, and intensity of their vegetative phenophases. We used a historical series of 60 years of precipitation observations for the Caatinga vegetation to define daily average of precipitation for rainy (Twet), median (Tcontrol), and dry (Tdry) years. We simulated past average daily rainfall (Twet, Tcontrol, and Tdry) while growing two herbaceous perennials and two herbaceous annuals. We monitored plant growth and measured the activity (absence or presence) and intensity of vegetative phenophases. We used circular statistical analysis to assess differences between treatments. Our results revealed that leaf production was seasonal but relatively uniform for perennial species and highly seasonal (wet season) for annual species. Simulated dry years induced lower leaf emergence concentrated over a few months in annual species, but this effect was more strongly significant in one of the two perennial species. Both annual and perennial species can experience delayed and less intense leaf abscission during the rainy season in years with below-average precipitation. In contrast, large voluminous rains in years with above-average precipitation can accelerate and intensify the process of leaf renewal. If future precipitation reductions occur, the changes in phenological response indicate that the cover of annual and perennial herbaceous species in this study will likely decrease, altering the landscape and functioning of dry tropical forests. However, the potential trade-offs observed may help populations of these species to persist during years of severe drought in the Caatinga.

Yield in many crops is affected by abscission during the early stages of fruitlet development. The reasons for fruitlet abscission are often unclear but they may include genetic factors because, in some crops, self-pollinated fruitlets are more likely to abscise than cross-pollinated fruitlets. Pollen parentage can also affect final fruit size and fruit quality. Here, we aimed to understand the effects of pollen parentage on fruitlet retention and nut quality in orchards of macadamia (Macadamia integrifolia Maiden & Betche). We identified the pollen parent of macadamia \'cultivar \'816\' embryos by analysing single nucleotide polymorphisms (SNPs) in their DNA using customised MassARRAY and Single Allele Base Extension Reaction (SABER) methods. This allowed us to determine the proportions of self-fertilised and cross-fertilised progeny during premature fruit drop at 6 weeks and 10 weeks after peak anthesis, as well as at nut maturity. We determined how pollen parentage affected nut-in-shell (NIS) mass, kernel mass, kernel recovery, and oil concentration. Macadamia trees retained cross-fertilised fruitlets rather than self-fertilised fruitlets. The percentage of progeny that were cross-fertilised increased from 6% at 6 weeks after peak anthesis to 97% at nut maturity, with each tree producing on average 22 self-fertilised nuts and 881 cross-fertilised nuts. Three of the four cross-pollen parents provided fruit with significantly higher NIS mass, kernel mass, or kernel recovery than the few remaining self-fertilised fruit. Fruit that were cross-fertilised by \'842\', \'A4\', or \'A203\' had 16-29% higher NIS mass and 24-44% higher kernel mass than self-fertilised fruit. Nuts that were cross-fertilised by \'A4\' or \'A203\' also had 5% or 6% higher kernel recovery, worth approximately $US460-540 more per ton for growers than self-fertilised nuts. The highly selective abscission of self-fertilised fruitlets and the lower nut quality of self-fertilised fruit highlight the critical importance of cross-pollination for macadamia productivity.

Plants have evolved mechanisms to abscise organs as they develop or when exposed to unfavorable conditions.1 Uncontrolled abscission of petals, fruits, or leaves can impair agricultural productivity.2,3,4,5 Despite its importance for abscission progression, our understanding of the IDA signaling pathway and its regulation remains incomplete. IDA is secreted to the apoplast, where it is perceived by the receptors HAESA (HAE) and HAESA-LIKE2 (HSL2) and somatic embryogenesis receptor kinase (SERK) co-receptors.6,7,8,9 These plasma membrane receptors activate an intracellular cascade of mitogen-activated protein kinases (MAPKs) by an unknown mechanism.10,11,12 Here, we characterize brassinosteroid signaling kinases (BSKs) as regulators of floral organ abscission in Arabidopsis. BSK1 localizes to the plasma membrane of abscission zone cells, where it interacts with HAESA receptors to regulate abscission. Furthermore, we demonstrate that YODA (YDA) has a leading role among other MAPKKKs in controlling abscission downstream of the HAESA/BSK complex. This kinase axis, comprising a leucine-rich repeat receptor kinase, a BSK, and an MAPKKK, is known to regulate stomatal patterning, early embryo development, and immunity.10,13,14,15,16 How specific cellular responses are obtained despite signaling through common effectors is not well understood. We show that the identified abscission-promoting allele of BSK1 also enhances receptor signaling in other BSK-mediated pathways, suggesting conservation of signaling mechanisms. Furthermore, we provide genetic evidence supporting independence of BSK1 function from its kinase activity in several developmental processes. Together, our findings suggest that BSK1 facilitates signaling between plasma membrane receptor kinases and MAPKKKs via conserved mechanisms across multiple facets of plant development.

PIN-FORMED (PIN) proteins, which function as efflux transporters, play many crucial roles in the polar transportation of auxin within plants. In this study, the exogenous applications of auxin IAA and TIBA were found to significantly prolong and shorten the florescence of tree peony (Paeonia suffruticosa Andr.) flowers. This finding suggests that auxin has some regulatory influence in petal senescence and abscission. Further analysis revealed a total of 8 PsPINs distributed across three chromosomes, which could be categorized into two classes based on phylogenetic and structural analysis. PsPIN1, PsPIN2a-b, and PsPIN4 were separated into the \"long\" PIN category, while PsPIN5, PsPIN6a-b, and PsPIN8 belonged to the \"short\" one. Additionally, the cis-regulatory elements of PsPIN promoters were associated with plant development, phytohormones, and environmental stress. These genes displayed tissue-specific expression, and phosphorylation sites were abundant throughout the protein family. Notably, PsPIN4 displayed distinct and elevated expression levels in roots, leaves, and flower organs. Expression patterns among the abscission zone (AZ) and adjacent areas during various flowering stages and IAA treatment indicate that PsPIN4 likely influences the initiation of peony petal abscission. The PsPIN4 protein was observed to be co-localized on both the plasma membrane and the cell nucleus. The ectopic expression of PsPIN4 reversed the premature flower organs abscission in the Atpin4 and significantly protracted florescence when introduced to Col Arabidopsis. Our findings established a strong basis for further investigation of PIN gene biological functions, particularly concerning intrinsic relationship between PIN-mediated auxin polar.

Sweet cherry (Prunus avium L.) is one of the most economically important fruits in the world. However, severe fruit abscission has brought significant challenges to the cherry industry. To better understand the molecular regulation mechanisms underlying excessive fruit abscission in sweet cherry, the fruit abscission characteristics, the anatomical characteristics of the abscission zone (AZ), as well as a homeodomain-Leucine Zipper gene family member PavHB16 function were analyzed. The results showed that the sweet cherry exhibited two fruit abscission peak stages, with the \"Brooks\" cultivar demonstrating the highest fruit-dropping rate (97.14%). During these two fruit abscission peak stages, both the retention pedicel and the abscising pedicel formed AZs. but the AZ in the abscising pedicel was more pronounced. In addition, a transcription factor, PavHB16, was identified from sweet cherry. The evolutionary analysis showed that there was high homology between PavHB16 and AtHB12 in Arabidopsis. Moreover, the PavHB16 protein was localized in the nucleus. Overexpression of PavHB16 in Arabidopsis accelerated petal shedding. In the PavHB16-overexpressed lines, the AZ cells in the pedicel became smaller and denser, and the expression of genes involved in cell wall remodeling, such as cellulase 3 gene (AtCEL3), polygalacturonase 1 (AtPG1), and expandin 24(AtEXPA24) were upregulated. The results suggest that PavHB16 may promote the expression of genes related to cell wall remodeling, ultimately facilitating fruit abscission. In summary, this study cloned the sweet cherry PavHB16 gene and confirmed its function in regulating sweet cherry fruit abscission, which provided new data for further study on the fruit abscission mechanism.
UNASSIGNED: The online version contains supplementary material available at 10.1007/s12298-024-01443-8.

JOINTLESS (J) was isolated in tomato (Solanum lycopersicum) from mutants lacking a flower pedicel abscission zone (AZ) and encodes a MADS-box protein of the SHORT VEGETATIVE PHASE/AGAMOUS-LIKE 24 subfamily. The loss of J function also causes the return to leaf initiation in the inflorescences, indicating a pivotal role in inflorescence meristem identity. Here, we compared jointless (j) mutants in different accessions that exhibit either an indeterminate shoot growth, producing regular sympodial segments, or a determinate shoot growth, due to the reduction of sympodial segments and causal mutation of the SELF-PRUNING (SP) gene. We observed that the inflorescence phenotype of j mutants is stronger in indeterminate (SP) accessions such as Ailsa Craig (AC), than in determinate (sp) ones, such as Heinz (Hz). Moreover, RNA-seq analysis revealed that the return to vegetative fate in j mutants is accompanied by expression of SP, which supports conversion of the inflorescence meristem to sympodial shoot meristem in j inflorescences. Other markers of vegetative meristems such as APETALA2c and branching genes such as BRANCHED 1 (BRC1a/b) were differentially expressed in the inflorescences of j(AC) mutant. We also found in the indeterminate AC accession that J represses homeotic genes of B- and C-classes and that its overexpression causes an oversized leafy calyx phenotype and has a dominant negative effect on AZ formation. A model is therefore proposed where J, by repressing shoot fate and influencing reproductive organ formation, acts as a key determinant of inflorescence meristems.

Plant glycoside hydrolase family 9 genes (GH9s) are widely distributed in plants and involved in a variety of cellular and physiological processes. In the current study, nine GH9 genes were identified in the mulberry and were divided into two subfamilies based on the phylogenetic analysis. Conserved motifs and gene structure analysis suggested that the evolution of the two subfamilies is relatively conserved and the glycoside hydrolase domain almost occupy the entire coding region of the GH9s gene. Only segmental duplication has played a role in the expansion of gene family. Collinearity analysis showed that mulberry GH9s had the closest relationship with poplar GH9s. MaGH9B1, MaGH9B6, MaGH9B5, and MaGH9B3 were detected to have transcript accumulation in the stalk of easy-to drop mature fruit drop, suggesting that these could play a role in mulberry fruit drop. Multiple cis-acting elements related to plant hormones and abiotic stress responses were found in the mulberry GH9 promoter regions and showed different activities under exogenous abscisic acid (ABA) and 2,4- dichlorophenoxyacetic acid (2,4-D) stresses. We found that the lignin content in the fruit stalk decreased with the formation of the abscission zone (AZ), which could indirectly reflect the formation process of the AZ. These results provide a theoretical basis for further research on the role of GH9s in mulberry abscission.