Comparative pollen morphological analysis in the subgenera Passiflora and Decaloba

Multi-integrated genomic data for Passiflora foetida provides insights into genome size evolution and floral development in Passiflora

Passiflora is a plant genus known for its extremely distinctive and colorful flowers and a wide range of genome size variation. However, how genome characteristics are related to flower traits among Passiflora species remains poorly understood. Here, we assembled a chromosome-scale genome of P. foetida, which belongs to the same subgenus as the commercial passionfruit P. edulis. The genome of P. foetida is smaller (424.16 Mb) and contains fewer copies of long terminal repeat retrotransposons (LTR-RTs). The disparity in LTR-RTs is one of the main contributors to the differences in genome sizes between these two species and possibly in floral traits. Additionally, we observed variation in insertion times and copy numbers of LTR-RTs across different transposable element (TE) lineages. Then, by integrating transcriptomic data from 33 samples (eight floral organs and flower buds at three developmental stages) with phylogenomic and metabolomic data, we conducted an in-depth analysis of the expression, phylogeny, and copy number of MIKC-type MADS-box genes and identified essential biosynthetic genes responsible for flower color and scent from glandular bracts and other floral organs. Our study pinpoints LRT-RTs as an important player in genome size variation in Passiflora species and provides insights into future genetic improvement.

Pliocene seeds of Passiflora subgenus Decaloba (Gray Fossil Site, Tennessee) and the impact of the fossil record on understanding the diversification and biogeography of Passiflora

PREMISE

Passiflora is a diverse genus of ~570 extant species primarily distributed in the Americas, from the eastern United States to Argentina and Chile. Nevertheless, the known fossil record of Passiflora is small. To date, only two fossil seed species have been unequivocally assigned to the genus. In this contribution, rare sulcate seeds from Gray Fossil Site are described as a third fossil seed species of Passiflora.

METHODS

Three partial seeds with sulcate sculpture from Gray Fossil Site, early Pliocene, Tennessee, USA, were examined, photographed, and measured. They were compared to samples of sulcate seeds from six extant Passiflora species in supersection Decaloba. A broader survey of sulcate seeds produced by modern species in the subgenera Decaloba, Deidamioides, and Tryphostemmatoides was done using published illustrations and descriptions.

RESULTS

The Gray Fossil Site seeds are described as Passiflora sulcatasperma, sp. nov., and assigned to subgenus Decaloba, supersection Decaloba. They are characterized by their small size, elliptical shape, ridged-and-sulcate sculpture, rugulose ridges, and thin palisade seed coat.

CONCLUSIONS

The two largest subgenera of Passiflora can be identified from Neogene fossils. Subgenus Decaloba is represented by two fossil seed species, P. bulgarica (Miocene, Bulgaria) and P. sulcatasperma (Pliocene, USA). Subgenus Passiflora is represented by fossil pollen (Miocene, Argentina and Brazil) and P. appalachiana seeds (Pliocene, USA). The distributions of fossil and modern species suggest that Passiflora may have used both North Atlantic and Antarctic routes to expand into Europe and the Asian-Oceanian Paleotropics, respectively.

Airborne transmission of biological agents within the indoor built environment: a multidisciplinary review

The nature and airborne dispersion of the underestimated biological agents, monitoring, analysis and transmission among the human occupants into building environment is a major challenge of today. Those agents play a crucial role in ensuring comfortable, healthy and risk-free conditions into indoor working and leaving spaces. It is known that ventilation systems influence strongly the transmission of indoor air pollutants, with scarce information although to have been reported for biological agents until 2019. The biological agents' source release and the trajectory of airborne transmission are both important in terms of optimising the design of the heating, ventilation and air conditioning systems of the future. In addition, modelling via computational fluid dynamics (CFD) will become a more valuable tool in foreseeing risks and tackle hazards when pollutants and biological agents released into closed spaces. Promising results on the prediction of their dispersion routes and concentration levels, as well as the selection of the appropriate ventilation strategy, provide crucial information on risk minimisation of the airborne transmission among humans. Under this context, the present multidisciplinary review considers four interrelated aspects of the dispersion of biological agents in closed spaces, (a) the nature and airborne transmission route of the examined agents, (b) the biological origin and health effects of the major microbial pathogens on the human respiratory system, (c) the role of heating, ventilation and air-conditioning systems in the airborne transmission and (d) the associated computer modelling approaches. This adopted methodology allows the discussion of the existing findings, on-going research, identification of the main research gaps and future directions from a multidisciplinary point of view which will be helpful for substantial innovations in the field.

Responses of Passiflora spp. to cowpea aphid-borne mosaic virus reveal infection in asymptomatic plants and new species with probable immunity

Passion fruit woodiness disease (PWD), caused by cowpea aphid-borne mosaic virus (CABMV), produces socioeconomic problems in Brazil. The objectives of this study were to i) evaluate the temporal progression of PWD, ii) identify Passiflora genotypes with resistance to CABMV, and iii) detect virus infection in asymptomatic plants by reverse transcription quantitative polymerase chain reaction (RT-qPCR) in cases where standard RT-PCR detection failed. The experiment was conducted in a greenhouse using 128 genotypes belonging to 12 species and three hybrids (inter- and intraspecific) of Passiflora, evaluated at five time points after inoculation. Progression rates and disease severity were lower in P. cincinnata, P. gibertii, P. miersii, and P. mucronata than in P. edulis, P. alata, Passiflora sp., and hybrids. Of the genotypes tested, 20.31% were resistant, especially the accessions of P. suberosa, P. malacophylla, P. setacea, P. pohlii, and P. bahiensis, which remained asymptomatic throughout the experiment. The absence of symptoms does not imply immunity of plants to the virus, since RT-qPCR analysis confirmed infection by the virus in asymptomatic plants of P. cincinnata, P. gibertii, P. miersii, P. mucronata, P. setacea, P. malacophylla, and P. suberosa. Even after four inoculations, the virus was not detected by RT-qPCR in the upper leaves in plants of the species P. pohlii and P. bahiensis, indicating that these species are probably immune to CABMV.

New trends in Passiflora L. pollen grains: morphological/aperture aspects and wall layer considerations

Passifloraceae shows a huge variability of pollen wall characteristics, most still little described. Passiflora is the largest genus with about 580 species with tropical distribution. Few studies in palynological approaches have described the intine layer which can fill existent gaps. Passiflora L. present four subgenera, from which Passiflora, Astrophea, and Decaloba were described in this study. The pollen wall variations were poorly studied, with the objective of describing the morphological and histochemical structure of Passiflora sporoderm that occurs in South America, aims to supply more pollen wall characters in some contexts. Besides the inference of evolutive trends, we described the number of apertures, type, reticule, and variations of the morphology and sporoderm and we related them with possible evolutive trends for the group. As a result, the pollen grains were not far from the patterns found by the literature, with exceptions. The species of the subgenus Passiflora have fused colpi, varying from 6 to 12 colpi, with type 2-reticulate exine. The species of the subgenus Astrophea have colporus and the species of Decaloba varied as the type of aperture, in which a new type of exine to be considered was found: the type 3. The subgenus Passiflora showed the thickest intine, slim endexine, and absent foot layer. While the species that belong to the other subgenera present a slim intine, the endexine is thick and the foot layer is continuous, among other variable characteristics. The size of the pollen grain seems to be related to the thickness of the intine, and consequently, related to possible pollinators. Through the cluster analysis, we reinforce the affinity of the species to its respective subgenus. To conclude, the analysis of the ultrastructure of the sporoderm and external morphology would be useful for an almost complete interpretation of the variations occurring in the genus, giving more information that the subgenus Passiflora is apomorphic when compared to the other two. The pollen wall characters should be considered on the interpretation of natural history, as well as the phylogenetic relationships of the family, mainly in the Passiflora genus, that has a large number of species distributed across the Neotropical regions.

Taxonomic study of subfamily Nepetoideae (Lamiaceae) by polynomorphological approach

The present study is insight into pollen morphology for characterizing species and their utility in the taxonomic separation of certain taxa of subfamily Nepetoideae (Lamiaceae) from Pakistan. The pollen micromorphology of 11 species of the Nepetoideae was analyzed and documented using light microscopy and scanning electron microscopy (SEM) for both qualitative and quantitative characteristics. Most species have hexazonocolpate pollen grains but trizonocolpate and tetrazonocolpate pollen with circular and oval amb were also rarely observed in Mentha spicata. The basic pollen shape in most of the studied species was subspheroidal but prolate grains were also observed in M. spicata, S. coccinea, and S. plebeia. The exine sculpturing of Nepetoideae pollen was taxonomically very informative particularly at subfamily level. Observations of exine sculpturing with SEM revealed various types of pollen grains: reticulate, bireticulate, microreticulate, perforate, aerolate, and gammate. The bireticulate type further subdivided into three subtypes based on the number of secondary lumina in each primary lumen and is characterized by varying characteristics of the secondary reticulum and primary muri. A significant variation was observed in colpus surface ornamentation. The maximum polar diameter was found in O. americanum (58 ± 5.8 μm) and the maximum equatorial diameter observed in O. basilicum (50.25 ± 1.37 μm). Pollen features of the studied species were discussed and compared based on the current taxonomical concepts. The results showed that pollen traits of the subfamily Nepetoideae was found significant to classify the taxa. Furthermore, pollen features provide additional evidence to distinguish macromorphologically similar taxa from each other.