In flowering plants, fertilization requires complex cell-to-cell communication events between the pollen tube and the female reproductive tissues, which are controlled by extracellular signaling molecules interacting with receptors at the pollen tube surface. We found that two such receptors in Arabidopsis, BUPS1 and BUPS2, and their peptide ligands, RALF4 and RALF19, are pollen tube–expressed and are required to maintain pollen tube integrity. BUPS1 and BUPS2 interact with receptors ANXUR1 and ANXUR2 via their ectodomains, and both sets of receptors bind RALF4 and RALF19. These receptor-ligand interactions are in competition with the female-derived ligand RALF34, which induces pollen tube bursting at nanomolar concentrations. We propose that RALF34 replaces RALF4 and RALF19 at the interface of pollen tube–female gametophyte contact, thereby deregulating BUPS-ANXUR signaling and in turn leading to pollen tube rupture and sperm release.

No abstract

Formaldehyde is a highly reactive compound that participates in multiple spontaneous reactions, but these are mostly deleterious and damage cellular components. In contrast, the spontaneous condensation of formaldehyde with tetrahydrofolate (THF) has been proposed to contribute to the assimilation of this intermediate during growth on C1 carbon sources such as methanol. However, the in vivo rate of this condensation reaction is unknown and its possible contribution to growth remains elusive. Here, we used microbial platforms to assess the rate of this condensation in the cellular environment. We constructed Escherichia coli strains lacking the enzymes that naturally produce 5,10-methylene-THF. These strains were able to grow on minimal medium only when equipped with a sarcosine (N-methyl-glycine) oxidation pathway that sustained a high cellular concentration of formaldehyde, which spontaneously reacts with THF to produce 5,10-methylene-THF. We used flux balance analysis to derive the rate of the spontaneous condensation from the observed growth rate. According to this, we calculated that a microorganism obtaining its entire biomass via the spontaneous condensation of formaldehyde with THF would have a doubling time of more than three weeks. Hence, this spontaneous reaction is unlikely to serve as an effective route for formaldehyde assimilation.

In Solanaceae, the -specific interaction between the pistil S-RNase and the pollen-Locus F-box protein controls self-incompatibility (SI). Although this interaction defines the specificity of the pollen rejection response, the identification of three pistil essential modifier genes unlinked to the -locus (, , and) unveils a higher degree of complexity in the pollen rejection pathway. We showed previously that NaStEP, a stigma protein with homology with Kunitz-type protease inhibitors, is essential to SI in spp. During pollination, NaStEP is taken up by pollen tubes, where potential interactions with pollen tube proteins might underlie its function. Here, we identified NaSIPP, a mitochondrial protein with phosphate transporter activity, as a novel NaStEP-interacting protein. Coexpression of NaStEP and NaSIPP in pollen tubes showed interaction in the mitochondria, although when expressed alone, NaStEP remains mostly cytosolic, implicating NaSIPP-mediated translocation of NaStEP into the organelle. The transcript is detected specifically in mature pollen of spp.; however, in self-compatible plants, this gene has accumulated mutations, so its coding region is unlikely to produce a functional protein. RNA interference suppression of NaSIPP in spp. pollen grains disrupts the SI by preventing pollen tube inhibition. Taken together, our results are consistent with a model whereby the NaStEP and NaSIPP interaction, in incompatible pollen tubes, might destabilize the mitochondria and contribute to arrest pollen tube growth.

Habanero (Capsicum chinense) is appreciated for its aroma and pungency; however, little is known of the stress effects on Habanero fruits. This work, through untargeted metabolomics, measures changes in the Habanero fruit pericarp under increased salinity and nitrogen and phosphorus deficiency at three ripening stages. Responses to salinity and macronutrient deficiency are stress-and ripening stage-specific, with a few features (<1% in N and P deficit; ca. 1.5% in salinity) being consistently affected through maturation, with the most evident changes in ripe fruit. Results point to a threshold in salinity, between 4 and 7 dS•m −1 , above which a measurable response is seen. Nitrogen deficiency has a symmetric effect on feature abundance, pointing at a metabolite substitution in the pericarp; in contrast, phosphorus deficiency leads to an overall reduction in metabolite diversity, which could negatively affect the postharvest shelf-life. This work shows that untargeted approaches help to improve our understanding of Habanero fruit metabolism under stress conditions beyond traditional metrics.

No abstract

The unambiguous identification of varieties within the Pseudostrobus complex is a key step to facilitate tree selection and monitoring in the wild as well as in plantations. Molecular tools provide a powerful approach for species delimitation; however, the use of DNA barcodes in this group has met limited success due to widespread haplotype sharing from lineage sorting, hybridization and introgression. Here, we evaluate the utility of real-time PCR coupled with high-resolution melting (HRM) to discriminate among Pinus pseudostrobus Lindl. var. pseudostrobus, apulcensis and oaxacana, from wild populations in central and southern Mexico, using chloroplast DNA sequence variants located within the clpP, ycf2, trnL(UAA)–trnT(UGU) and trnI(CAU)–trnF(GAA) loci. The markers ycf2/trnL(UAA)–trnT(UGU) produced clear melting patterns that separated the varieties pseudostrobus and oaxacana from type var. apulcensis, whereas clpP discriminated over 60% of var. oaxacana individuals. This assay underlines the usefulness of these less-used DNA regions as potential biological markers and exhibits the effect of geography on allele distribution and the likely presence of hybrids among the species and varieties.

Seed banks represent an important strategy for the conservation of forest genetic resources, although a basic understanding of the physiological changes that seeds undergo during storage that affect quality and germination is still lacking for most tropical and subtropical species. Here, we describe the optimisation of an RNA isolation procedure and reference gene normalisation for expression analysis in Cedrela odorata (cedro or Spanish cedar) seeds during different physiological states, as well as in the steady-state stem and leaf. The expression profiles of five endogenous candidate reference genes (18S, EF1α, GAPDH, CDC27B, PP2A2) and an exogenous (HMBS) gene were evaluated by using dedicated algorithms, including Genorm, Normfinder, Bestkeeper and ΔCt. We found that the expression of all endogenous genes varied considerably in response to both ageing and hydration. Therefore, using the external HMBS was a suitable alternative to evaluate gene expression in these highly contrasting physiological conditions. The reference genes EF1α and GAPDH were the most stable, and could be used for normalisation of qRT-PCR results under specific circumstances.