Sex-specific variation in the interaction between Distichlis spicata (Poaceae) and mycorrhizal fungi

How does plant sex alter microbiota assembly in dioecious plants?

Plant microbiota can greatly impact plant growth, defense, and health in different environments. Thus, it might be evolutionarily beneficial for plants to be able to control processes related to microbiota assembly. Dioecious plant species display sexual dimorphism in morphology, physiology, and immunity. These differences imply that male and female individuals might differently regulate their microbiota, but the role of sex in microbiota assembly has been largely neglected so far. Here, we introduce the mechanism of how sex controls microbiota in plants analogically to the sex regulation of gut microbiota in animals, in particular in humans. We argue that plant sex imposes selective pressure on filtering and constructing microbiota in the rhizosphere, phyllosphere, and endosphere along the soil-plant continuum. Since male plants are more resistant than female plants to environmental stresses, we suggest that a male host forms more stable and resistant plant microbiota that cooperate more effectively with the host to resist stresses. Male and female plants can distinguish whether a plant is of the same or different sex, and males can alleviate stress-caused damage in females. The impact of a male host on microbiota would protect female plants from unfavorable environments.

JC, McFarland K, Goffinet B. Population Genomics and Phylogeography of a Clonal Bryophyte With Spatially Separated Sexes and Extreme Sex Ratios

The southern Appalachian (SA) is one of the most biodiversity-rich areas in North America and has been considered a refugium for many disjunct plant species, from the last glacial period to the present. Our study focuses on the SA clonal hornwort, Nothoceros aenigmaticus J. C. Villarreal & K. D. McFarland. This hornwort was described from North Carolina and is widespread in the SA, growing on rocks near or submerged in streams in six and one watersheds of the Tennessee (TR) and Alabama (AR) Rivers, respectively. Males and female populations occur in different watersheds, except in the Little Tennessee (TN) River where an isolated male population exists ca. 48 km upstream from the female populations. The sex ratio of 1:0 seems extreme in each population. In this study, we use nuclear and organellar microsatellites from 250 individuals from six watersheds (seven populations) in the SA region and two populations from Mexico (23 individuals). We, then, selected 86 individuals from seven populations and used genotyping by sequencing to sample over 600 bi-allelic markers. Our results suggest that the SA N. aenigmaticus and Mexican plants are a nested within a clade of sexual tropical populations. In the US populations, we confirm an extreme sex ratio and only contiguous US watersheds share genotypes. The phylogenetic analysis of SNP data resolves four clusters: Mexican populations, male plants (Little Pigeon and Pigeon river watersheds) and two clusters of female plants; one from the Little Tennessee and Hiwassee Rivers (TR) and the other from the Ocoee (TR) and Coosa (AR) Rivers. All clusters are highly differentiated (Fst values over 0.9). In addition, our individual assignment analyses and PCAs reflect the phylogenetic results grouping the SA samples in three clades and recovering males and female plants with high genetic differentiation (Fst values between 0.5 and 0.9 using microsatellites and bi-allelic markers). Our results point to Pleistocene events shaping the biogeographical pattern seen in US populations. The extreme sex ratio reflects isolation and highlights the high vulnerability of the populations in the SA.

Sex-specific strategies of phosphorus (P) acquisition in Populus cathayana as affected by soil P availability and distribution

Soil phosphorus (P) availability and its distribution influence plant growth and productivity, but how they affect the growth dynamics and sex-specific P acquisition strategies of dioecious plant species is poorly understood. In this study, the impact of soil P availability and its distribution on dioecious Populus cathayana was characterized. P. cathayana males and females were grown under three levels of P supply, and with homogeneous or heterogeneous P distribution. Females had a greater total root length, specific root length (SRL), biomass and foliar P concentration under high P supply. Under P deficiency, males had a smaller root system than females but a greater exudation of soil acid phosphatase, and a higher colonization rate and arbuscular mycorrhizal hyphal biomass, suggesting a better capacity to mine P and a stronger association with arbuscular mycorrhizal fungi to forage P. Heterogeneous P distribution enhanced growth and root length density (RLD) in females. Female root proliferation in P-rich patches was related to increased foliar P assimilation. Localized P application for increasing P availability did not enhance the biomass accumulation and the morphological plasticity of roots in males, but it raised hyphal biomass. The findings herein indicate that sex-specific strategies in P acquisition relate to root morphology, root exudation and mycorrhizal symbioses, and they may contribute to sex-specific resource utilization patterns and niche segregation.

Additional AM Fungi Inoculation Increase Populus cathayana Intersexual Competition

Sex-specific responses to mycorrhiza have been reported in dioecious plant species, but little attention has been paid to the influence of arbuscular mycorrhizal (AM) fungi on competitive ability under intersexual competition. To further address whether this competition is affected by an additional AM fungi supply, Populus cathayana saplings were chosen and subjected to two mycorrhizal treatments [inoculated and non-inoculated (control) with an additional AM fungi Funneliformis mosseae] while growing with the opposite sex for 3 months. Compared with the control, the additional AM fungi inoculation induced P. cathayana saplings to exhibit significant sexual differences in root structure and nutrient uptake (e.g., cortical layer, cross-section area, radius of root tips, and N, K, and Mg content), and enlarged sexual differences in morphology and biomass accumulation (e.g., leaf number increment, shoot height increment, total leaf area, total specific root length, stem dry mass, leaf dry mass, and total dry mass). Meanwhile, inoculated females presented higher values in most of these traits mentioned above than males under intersexual competition. Therefore, we conclude that the intersexual competition can be increased by an additional AM fungi supply, with females gaining more symbiosis-mediated benefits than males.

Sex-specific morphological and physiological differences in the moss Ceratodon purpureus (Dicranales)

BACKGROUND AND AIMS

Dioecy and sexual dimorphism occur in many terrestrial plant species but are especially widespread among the bryophytes. Despite the prevalence of dioecy in non-vascular plants, surprisingly little is known about how fine-scale sex-specific cell and leaf morphological traits are correlated with sex-specific physiology and population sex ratios. Such data are critical to understanding the inter-relationship between sex-specific morphological and physiological characters and how their relationship influences population structure. In this study, these data types were assessed to determine how they vary across three populations within one moss species and whether fine-scale morphological traits scale up to physiological and sex ratio characteristics.

METHODS

Twenty cell-, leaf- and canopy-level traits and two photochemical measurements were compared between sexes and populations of the dioecious moss Ceratodon purpureus . Field population-expressed sex ratios were obtained for the same populations.

KEY RESULTS

Male and female plants differed in cell, leaf and photochemical measures. These sexual dimorphisms were female biased, with females having larger and thicker leaves and greater values for chlorophyll fluorescence-based, leaf photochemistry measurements than males. Female traits were also more variable than male traits. Interestingly, field population sex ratios were significantly male biased in two study populations and female biased in the third study population.

CONCLUSIONS

The results demonstrate that the larger morphology and the greater physiological output of female C. purpureus gametophytes compared with males occurs across populations and is likely to have significant effects on resource allocation and biotic interactions. However, this high level of dimorphism does not explain population sex ratio variation in the three study populations tested. This research lays the groundwork for future studies on how differential sex-specific variation in cell and leaf traits influences bryophyte plant fitness.

Climate change perils for dioecious plant species

Climate change, particularly increased aridity, poses a significant threat to plants and the biotic communities they support. Dioecious species may be especially vulnerable to climate change given that they often exhibit spatial segregation of the sexes, reinforced by physiological and morphological specialization of each sex to different microhabitats. In dimorphic species, the overexpression of a trait by one gender versus the other may become suppressed in future climates. Data suggest that males will generally be less sensitive to increased aridity than co-occurring females and, consequently, extreme male-biased sex ratios are possible in a significant number of populations. The effects of male-biased sex ratios are likely to cascade to dependent community members, especially those that are specialized on one sex.

Effects of arbuscular mycorrhizal fungi and maternal plant sex on seed germination and early plant establishment

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PREMISE OF THE STUDY

Arbuscular mycorrhizal fungi usually enhance overall plant performance, yet their effects on seed germination and early plant establishment, crucial steps in plant cycles, are generally overlooked. In gynodioecious species, sexual dimorphism in these traits has been reported, with females producing seeds that germinate at a faster rate than seeds from hermaphrodites.•

METHODS

Using the gynodioecious plant Geranium sylvaticum, I investigated in a greenhouse experiment whether the presence of arbuscular mycorrhizal spores affects seed germination and early plant establishment, examining at the same time whether the sex of the mother producing the seeds also influences these parameters and whether sex-specific interactions between these two factors exist.•

KEY RESULTS

The presence of arbuscular mycorrhizal spores in the soil decreased seed germination, did not affect plant survival, but did increase plant growth. Moreover, no significant differences in seed traits were detected between the sexes of the plants producing the seeds.•

CONCLUSIONS

This study demonstrates that arbuscular mycorrhizal fungi may have contrasting effects for plants during early life stages and that mycorrhizal effects can take place even at the precolonization stage.

Sex-specific interaction between arbuscular mycorrhizal and dark septate fungi in the dioecious plant Antennaria dioica (Asteraceae)

Male and female plants of dioecious species often differ in their resource demands and this has been linked to secondary sexual dimorphism, including sex-specific interactions with other organisms such as herbivores and pollinators. However, little is known about the interaction between dioecious plants and fungal root endophytes. Plants may be simultaneously colonised by arbuscular mycorrhizal (AM) and dark septate (DS) fungi. While it is well established that AM mutualism involves reciprocal transfer of photosynthates and mineral nutrients between roots of host plants and these fungi, the role of DS fungi remains controversial. Here, we report the temporal and spatial variation in AM and DS fungi in female, male and non-reproductive Antennaria dioica plants in three natural populations in Finland during flowering and after seed production. Females had higher colonisation by AM fungi, but lower colonisation by DS fungi than male and non-reproductive plants. The higher AM colonisation was observed during flowering, and this difference varied among populations. Our results suggest that females and males of A. dioica interact with AM and DS fungi differently and that this relationship is dependent on soil fertility.

Plasticity tradeoffs in salt tolerance mechanisms among desert Distichlis spicata genotypes

We investigated genetic differences in salinity tolerance among 20 saltgrass (Distichlis spicata (L.) Greene) genotypes, including constitutive, gender-based and phenotypic plasticity traits, to better understand the basis of adaptation and acclimation by saltgrass in diverse environments. On average, the plants survived NaCl treatments up to ~1M, with reductions in growth and health that varied with genotype. For these 20 genotypes in a greenhouse study, we showed that greater plasticity in one salt tolerance mechanism was physiologically linked to lesser plasticity in another. Under various levels of constant salinity stress, genotypes employing a strategy of greater plasticity in foliar Na and lesser plasticity in both foliar K:Na and Na turnover rate were better able to substitute Na for K in some cellular functions, especially osmotic adjustment, leading to increased salinity tolerance. Although we observed gender segregation with salinity in the Owens (Dry) Lake Playa (Inyo County, CA, USA) population planted for dust control, from which the genotypes were collected, we did not observe gender differences in salinity tolerance in the greenhouse. Significant physiological plasticity tradeoffs among genotypes, however, did affect overall salinity tolerance and may be important for this species survival in diverse managed and natural habitats.

Dioecious Silene latifolia plants show sexual dimorphism in the vegetative stage

BACKGROUND

Prior to this study, no differences in gene expression between male and female dioecious plants in the vegetative state had been detected. Among dioecious plants displaying sexual dimorphism, Silene latifolia is one of the most studied species. Although many sexually dimorphic traits have been described in S. latifolia, all of them are quantitative, and they usually become apparent only after the initiation of flowering.

RESULTS

We present RT-PCR-based evidence that in S. latifolia, sexual dimorphism in gene expression is present long before the initiation of flowering. We describe three ESTs that show sex-specific (two male specific and one female specific) transcription at the rosette stage before the first flowering season.

CONCLUSIONS

To our knowledge, this study provides the first molecular evidence of early pre-flowering sexual dimorphism in angiosperms.

Inter-sexual competition in a dioecious grass

Spatial segregation of the sexes (SSS) occurs in many dioecious angiosperms, but little data are available on the fitness advantages, if any, for males and females. We examined whether reciprocally transplanted male and female seedlings of Distichlis spicata, a dioecious grass species that exhibits extreme SSS, differed in their responses to microhabitats and competition treatments. Plants grown without conspecific competitors grew equally well in both male- or female-majority habitats, suggesting that male and female plants do not have differential resource needs at the juvenile life-history stage. However, plants subject to intra-sexual competition were significantly larger than plants subject to inter-sexual competition, suggesting that niche partitioning may occur in D. spicata.