Biology subjects

Bemer, M.

Publications and source records attributed to Bemer, M..

6 recordsLinked to original sources

bioRxiv2026

Secondary growth in the tomato stem is suppressed by the flowering regulators FUL2 and STM3

Herbaceous eudicot crops such as tomato accumulate substantial amounts of secondary xylem in their stems, particularly in the basal part. As plants progress from the vegetative phase to flowering and fruit development, secondary growth continues to provide mechanical support and facilitate transport. To uncover how secondary growth is regulated in the tomato stem, we used laser capture microdissection RNA-seq to establish tissue-specific transcriptomic profiles. This revealed that key regulators associated with wood formation in poplar are also acting in tomato. Furthermore, we found that the flowering regulators FUL2 and STM3 are substantially expressed in xylem tissue. Subsequent functional analysis identified FUL2 and STM3 as key repressors of secondary growth, with ful2 or stm3 knock-out mutants exhibiting strongly increased secondary growth in older tomato stems. Notably, a higher order mutant in which both ful2 and stm3 were knocked out displays a similar non-additive phenotype, indicating, together with yeast two-hybrid data showing physical interaction, that FUL2 and STM3 act together in a complex. The expression levels of both genes remain low until after the floral transition but strongly rise during subsequent stem development. Transcriptomic analyses in ful2, stm3, and wild-type stems at stages before and after detectable anatomical differences, showed that the FUL2-STM3 complex represses distinct sets of NAC and MYB candidate regulators associated with xylem development. Interestingly, FUL2 and STM3 control these regulators in a stage- and position-dependent way, with candidates showing upregulation only at later stages in mid-height stems being already upregulated at earlier stages in basal stem regions. Our findings provide a tissue-resolved transcriptomic resource for tomato stems and reveal a role for FUL2 and STM3 in limiting secondary xylem accumulation as stem development progresses.

plant biology↗

bioRxiv2026

SELF-PRUNING 5G interplays with age and gibberellin pathways downstream of SlCOL1 to orchestrate photoperiodic tomato flowering

Tomato (Solanum lycopersicum) is classified as a day-neutral plant, whereas its wild relatives exhibit delayed flowering under long day (LD) conditions due to higher activity of the SELF-PRUNING 5G (SP5G). In Arabidopsis thaliana, CONSTANS (CO) activates FLOWERING LOCUS T (FT), a homolog of SP5G, but whether and how CO integrates with SP5G in tomato flowering was unclear. Here, we demonstrate that SlCOL1 (the tomato CO homolog) delays flowering by directly activating SP5G in a PHYTOCHROME B1 (PHYB1)-dependent manner. Importantly, genetic and molecular analyses combining a photoperiod-responsive tomato line carrying the wild SP5G allele from S. pennellii, together with SlCOL1 and flowering-pathway mutants, revealed synergistic crosstalk among the photoperiodic SlCOL1-SP5G module, age-dependent pathway (mediated mainly by the microRNA156-SlSBP module), gibberellin (GA) pathway, and SINGLE FLOWER TRUSS (SFT) pathway. Mechanistically, we show that SP5G forms a complex with miR156-targeted SlSBP13 to directly regulate SFT expression, and that GA may interfere with SP5G activity. Together, these findings revealed a coordinated network that integrates multiple flowering signals to modulate both shared and pathway-specific targets. Our findings provide a significant advance in understanding the molecular regulation of tomato flowering and offer promising avenues for breeding strategies optimized for diverse environmental conditions and latitudes.

plant biology↗

bioRxiv2026

The FUL-SHP-AP2 module regulates fruit development in petunia

Fruit development is a typical angiosperm feature that greatly facilitates seed dispersal. Despite extensive studies on the gene regulatory network underlying pod shattering in the dry Arabidopsis fruit and the ripening process in the fleshy tomato fruit, it is yet unclear if a conserved regulatory network acts in early fruit development. Here, we investigated the roles of Petunia x hybrida (petunia) FRUITFULL (FUL), SHATTERPROOF (SHP) and APETALA 2 (AP2) homologs, three types of transcription factors repeatedly associated with fruit development and/or ripening. Petunia is closely related to tomato but produces dry dehiscent fruits like Arabidopsis. Our functional analysis revealed that the three petunia FUL-like genes, PETUNIA FLOWERING GENE (PFG), FLORAL BINDING PROTEIN 26 (FBP26) and FBP29, redundantly regulate endocarp development. They promote the formation of regularly shaped inner endocarp cells, probably via auxin/brassinosteroid signalling and cell wall modification. Furthermore, we discovered that the SHP-like gene FLORAL BINDING PROTEIN 6 (FBP6) has an opposite role, promoting more mesocarp-shaped endocarp cells, indicating that the FUL-like and SHP-like genes act antagonistically in early pericarp development. Finally, we show that the AP2-like genes REPRESSOR OF B-FUNCTION 1 (ROB1), ROB2 and ROB3 are crucial factors in petunia fruit development. rob1 rob2 rob3 mutants completely fail to dehisce and show major defects in pericarp patterning. The ROB transcription factors repress the activity of the FUL-like genes, and have, together with FBP6, an opposite effect on auxin and brassinosteroid signalling genes. Our study suggests that a module consisting of antagonistically acting TFs, including co-orthologs of AP2, FUL and SHP, regulates early pericarp patterning, at least partially via auxin and brassinosteroids.

plant biology↗

bioRxiv2020

The Polycomb group protein MEDEA controls cell proliferation and embryonic patterning in Arabidopsis

Establishing the body plan of a multicellular organism relies on precisely orchestrated cell divisions coupled with pattern formation. In animals, cell proliferation and embryonic patterning are regulated by Polycomb group (PcG) proteins that form various multisubunit complexes (Grossniklaus and Paro, 2014). The evolutionary conserved Polycomb Repressive Complex 2 (PRC2) trimethylates histone H3 at lysine 27 (H3K27me3) and comes in different flavors in the model plant Arabidopsis thaliana (Forderer et al., 2016; Grossniklaus and Paro, 2014). The histone methyltransferase MEDEA (MEA) is part of the FERTILIZATION INDEPENDENT SEED (FIS)-PRC2 required for seed development4. Although embryos derived from mea mutant egg cells show morphological abnormalities (Grossniklaus et al., 1998), defects in the development of the placenta-like endosperm are considered the main cause of seed abortion (Kinoshita et al., 1999; Scott et al., 1998), and a role of FIS-PRC2 in embryonic patterning was dismissed (Bouyer et al., 2011; Leroy et al., 2007). Here, we demonstrate that endosperm lacking MEA activity sustains normal embryo development and that embryos derived from mea mutant eggs abort even in presence of a wild-type endosperm because MEA is required for embryonic patterning and cell lineage determination. We show that, similar to PcG proteins in mammals, MEA regulates embryonic growth by repressing the transcription of core cell cycle components. Our work demonstrates that Arabidopsis embryogenesis is under epigenetic control of maternally expressed PcG proteins, revealing that PRC2 was independently recruited to control embryonic cell proliferation and patterning in animals and plants.

developmental biology↗

bioRxiv2020

FRUITFULL-like genes regulate flowering time and inflorescence architecture in tomato

The timing of flowering and inflorescence architecture are critical for the reproductive success of tomato, but the gene regulatory networks underlying these traits have not been fully explored. Here we show that the tomato FRUITFULL-like (FUL-like) genes FUL2 and MADS-BOX PROTEIN 20 (MBP20) induce flowering and repress inflorescence branching by promoting floral meristem determinacy. FUL1 fulfils a less prominent role and appears to depend on FUL2 and MBP20 for its upregulation in the inflorescence- and floral meristems. MBP10, the fourth tomato FUL-like gene, has probably lost its function. The tomato FUL-like proteins cannot homodimerize in in vitro assays, but heterodimerize with various other MADS-domain proteins, potentially forming distinct complexes in the transition meristem and floral meristem. Transcriptome analysis of the primary shoot meristems revealed various interesting downstream targets, including four repressors of cytokinin signalling that are upregulated during the vegetative-to-reproductive transition in ful1 ful2 mbp10 mbp20 mutants. FUL2 and MBP20 can also bind in vitro to the upstream regions of these genes, thereby probably directly stimulating cell division in the meristem upon the transition to flowering. The control of inflorescence branching does not occur via the CKXs, but appears regulated by repression of transcription factors such as TM3, APETALA 2b (AP2b) and AP2a.

plant biology↗

bioRxiv2020

A suppressor of axillary meristem maturation promotes longevity in flowering plants

Post embryonic development and growth of flowering plants are for a large part determined by the activity and maturation state of stem cell niches formed in the axils of leaves, the so-called axillary meristems (AMs)1,2. Here we identify a new role for the Arabidopsis AT-HOOK MOTIF CONTAINING NUCLEAR LOCALIZED 15 (AHL15) gene as a suppressor of AM maturation. Loss of AHL15 function accelerates AM maturation, whereas ectopic expression of AHL15 suppresses AM maturation and promotes longevity in Arabidopsis and tobacco. Together our results indicate that AHL15 expression acts as a key molecular switch, directly downstream of flowering genes (SOC1, FUL) and upstream of GA biosynthesis, in extending the plants lifespan by suppressing AM maturation.

plant biology↗