Mycorrhizal Switching and the Role of Fungal Abundance in Seed Germination in a Fully Mycoheterotrophic Orchid, Gastrodia confusoides

Mycorrhizal associations are essential for orchid germination and seedling establishment, and thus may constrain the distribution and abundance of orchids under natural conditions. Previous studies have shown that germination and seedling establishment in several orchids often decline with increasing distance from adult plants, resulting in non-random spatial patterns of seedling establishment. In contrast, individuals of the fully mycoheterotrophic orchid Gastrodia confusoides often tend to have random aboveground spatial patterns of distribution within bamboo forests. Since G. confusoides is parasitic on litter-decaying fungi, its random spatial patterns of distribution may be due to highly scattered patterns of litter-decaying fungi within bamboo forests. To test this hypothesis, we first identified the main mycorrhizal fungi associating with developing seeds and adult plants at a bamboo forest site in Taiwan using Miseq high-throughput DNA sequencing. Next, we combined seed germination experiments with quantitative PCR (qPCR) analyses to investigate to what extent the abundance of mycorrhizal fungi affected spatial patterns of seed germination. Our results show that seed germination and subsequent growth to an adult stage in G. confusoides required a distinct switch in mycorrhizal partners, in which protocorms associated with a single Mycena OTU, while adults mainly associated with an OTU from the genus Gymnopus. A strong, positive relationship was observed between germination and Mycena abundance in the litter, but not between germination and Gymnopus abundance. Fungal abundance was not significantly related to the distance from the adult plants, and consequently germination was also not significantly related to the distance from adult plants. Our results provide the first evidence that the abundance of litter-decaying fungi varies randomly within the bamboo forest and independently from G. confusoides adults.

Is the South-Mediterranean Canopy-Forming Ericaria giacconei (= Cystoseira hyblaea) a Loser From Ocean Warming?

Canopy-forming brown algae support highly productive ecosystems whose decline has been attributed to the interplay of several anthropogenic disturbances. Climate change could have disruptive effects on the biology of these species, but the role of temperature in the development of early life stages is poorly understood. The aim of this study was to assess the response of Ericaria giacconei, a winter-reproducing Southern–Mediterranean endemic species, to thermal stress by testing five temperatures (12, 15, 18, 24, and 28°C) on adults and early stages. Chlorophyll a fluorescence of adult plants was measured at 0, 24, 72, and 120 h on nine fronds in each of the three aquaria per treatment. To assess egg release, zygote settlement, and embryo growth rate, approximately 1,200 receptacles were cultured on six Petri dishes per temperature treatment, and 10 random subsections of 2 ×2 mm were examined in three Petri dishes at 0, 20, 44, and 92 h after fertilization. Adult plants showed a plastic physiological response, and thermal stress had no significant effect on PSII efficiency. Embryos fully developed only at 12 and 15°C. Mortality increased at 18 and 24°C, and no zygotes survived at 28°C. In a scenario of further increasing temperatures, the effects of warming could affect the recruitment of E. giacconei and increase its vulnerability to further stresses. These effects on the survival of early stages, which are the bottleneck for the long-term survival of the species, should be taken into account in conservation and restoration measures to maintain canopy-forming macroalgal populations and associated biodiversity and ecosystem services.

State of Cenopopulations of Trommsdorffia ciliata (Thunb.) H.S. Pak (Asteraceae) in the Plant Communities of the Lower Reaches of the Ussuri River

The paper presents the results of studying the structure and state of four cenopopulations of the rare species Trommsdorffia ciliata (Thunb.) H.S. Pak in the valley of the lower reaches of the Ussuri River. The density of the studied cenopopulations is from 8 to 27 ind./m2. All studied cenopopulations are normal and incomplete. The absence or small number of juveniles in the ontogenetic spectrum of the studied cenopopulations is associated with a high projective cover of the herbaceous layer, which prevents the survival of this age group. According to the absolute maximum of ontogenetic groups of adult plants of all cenopopulations, Trommsdorffia ciliata are classified as young normal ones, where the maximum falls on individuals of the virginal state. An evaluation of population and organismic signs of the state of the studied cenopopulations showed that the most favorable conditions for the growth of Trommsdorffia ciliata are formed in a moist sedge-grass-herb meadow in the vicinity of Lonchakovo village. The measures for the protection of Trommsdorffia ciliata that are to include in the Red Book of the Khabarovsk krai (2019), to inhabit in a protected area and are to control the state of the known population of this species have been cited.

A Null Allele of the Pol IV Second Subunit is Viable in Oryza sativa

All eukaryotes possess three DNA-dependent RNA polymerases, Pols I-III, while land plants possess two additional polymerases, Pol IV and Pol V. Derived through duplication of Pol II subunits, Pol IV produces 24-nt siRNAs that interact with Pol V transcripts to target de novo DNA methylation and silence transcription of transposons. Members of the grass family encode additional duplicated subunits of Pol IV and V, raising questions regarding the function of each paralog. In this study, we identify a null allele of the putative Pol IV second subunit, NRPD2, and demonstrate that NRPD2 is the sole subunit functioning with NRPD1 in small RNA production and CHH methylation in leaves. Homozygous nrpd2 mutants have neither gametophytic defects, nor embryo lethality, although adult plants are dwarf and sterile.

FEASIBILITY OF EARLY Pinus taeda L. SELECTION TO ASSESS GROWTH VARIABLES IN PROGENY TEST

Forest species breeding programs require a long period-of-time for plants to reach the proper age to enable selecting superior genotypes, which is a critical factor in selection processes. Thus, the aims of the current study are to estimate genetic parameters in juvenile and adult plants (6, 10 and 20 years) in order to investigate genetic correlations between variables at different ages and at certain ages; as well as to determine whether it is possible performing efficient early selection in juvenile plants. The test was implemented in 1997; it comprised 120 progenies and followed a randomized block design, with five repetitions - linear plots comprised 5 plants at 2.5 m x 2.5 m spacing. DBH (cm), H (m) and VOL (m³) of all tested subjects were measured at the age of 6, 10 and 20 years. Variance components, genetic parameters, as well as genetic correlations between variables and between ages were estimated in Selegen REML/BLUP® software. Genetic parameter estimates have shown superiority at 10 years, in comparison to that estimated at 6 and 20 years. Variable ‘DBH’ has shown high genetic correlation to height (H) and volume (VOL), whereas DBH x VOL have shown high genetic correlation (0.98) in 10-year-old plants. With respect to genetic correlation between ages, 10-year-old plants have shown moderate correlation to 6- and 20-year-old plants. Early selection is indicated for 10-year-old plants, in 20-year cycles, since plants at this age have shown higher selection efficiency to predict gains in comparison to adult plants.

Adult plant resistance to white rust in Lunaria annua

Wild plants produce abundant seeds and seedlings, but most die before reaching maturity, and these premature deaths are often caused by pathogens. Major genes for resistance protect some seedlings or juveniles. These selected individuals can become a resistant, mature cohort. Alternatively, plants can exhibit mature, adult plant resistance. These two explanations can be indistinguishable in the field, when epidemics in natural pathosystems occur regularly resulting in annual selection for resistance. This study included multi-year observations of a biennial plant where the distinction could be made. White rust of Lunaria annua, a pathosystem native to the Mediterranean Basin, took time in its introduced range in Idaho, USA, to generate epidemics. After years of minimal white rust, an epidemic occurred in 2017 in which first-year, juvenile plants had 20 times the sorus density of second-year, adult plants. Since white rust incidence had been minimal for years prior to 2017, the greater resistance of 2017 adults over 2017 juveniles may have been due to adult-plant resistance. This could also be due to phenology: adult plants have mature leaves, and are flowering and maturing seed, by the time that white rust begins to build up on leaves of juveniles. The juvenile-adult difference was maintained in 2018. In white blister rusts, interpretation of resistance can also be complicated by the frequency of asymptomatic infections that adult plants would pass on to the next generation. However, we found no asymptomatic infection of seeds of L. annua in our sampling of the Idaho population.

Contributions of environmental and maternal transmission to the assembly of leaf fungal endophyte communities

Leaf fungal endophytes (LFEs) contribute to plant growth and responses to stress. Fungi colonize leaves through maternal transmission, e.g. via the seed, and through environmental transmission, e.g. via aerial dispersal. The relative importance of these two pathways in assembly and function of the LFE community is poorly understood. We used amplicon sequencing to track switchgrass ( Panicum virgatum ) LFEs in a greenhouse and field experiment as communities assembled from seed endophytes and rain fungi (integration of wet and dry aerial dispersal) in germinating seeds, seedlings, and adult plants. Rain fungi varied temporally and hosted a greater portion of switchgrass LFE richness (greater than 65%) than were found in seed endophytes (greater than 25%). Exposure of germinating seeds to rain inoculum increased dissimilarity between LFE communities and seed endophytes, increasing the abundance of rain-derived taxa, but did not change diversity. In the field, seedling LFE composition changed more over time, with a decline in seed-derived taxa and an increase in richness, in response to environmental transmission than LFEs of adult plants. We show that environmental transmission is an important driver of LFE assembly, and likely plant growth, but its influence depends on both the conditions at the time of colonization and plant life stage.

Mutualistic interactions between B. subtilis and seeds dictate plant development

A tightly coordinated developmental program controls precise genetic and metabolic reprogramming that dictates efficient transition of the seeds from dormancy to metabolically active seedlings. Beneficial microbes are known to stimulate the germination of the seeds or adaptation of the seedlings; however, investigations of exact mechanisms mediating these interactions and the resulting physiological responses of the plants are only beginning. Bacillus subtilis is commonly detected in the plant holobiont and belongs to the group of microbes that provide multifaceted contribution to the health of the plants. The present study demonstrated that B. subtilis triggered genetic and physiological responses in the seeds that determined subsequent metabolic and developmental status of adult plants. Chemically diverse extracellular matrix of Bacillus was demonstrated to structurally cooperate in bacterial colonization of the seed storage tissues. Additionally, an amyloid protein and fengycin, which are two components of the extracellular matrix, targeted the oil bodies of the seed endosperm, provoking changes in lipid metabolism or accumulation of glutathione-related molecules that stimulated two different plant growth programs: the development of seed radicles or overgrowth and immunization of adult plants. We propose this mutualistic interaction is conserved in Bacilli and plant seeds containing storage oil bodies.

Ontogenetic Changes in the Chemical Profiles of Piper Species

The chemical composition of seedlings and adult plants of several Piper species were analyzed by 1H NMR spectroscopy combined with principal component analysis (PCA) and HPLC-DAD, HPLC-HRESIMS and GC-MS data. The chromatographic profile of crude extracts from leaves of Piper species showed remarkable differences between seedlings and adult plants. Adult leaves of P. regnellii accumulate dihydrobenzofuran neolignans, P. solmsianum contain tetrahydrofuran lignans, and prenylated benzoic acids are found in adult leaves of P. hemmendorffii and P. caldense. Seedlings produced an entirely different collection of compounds. Piper gaudichaudianum and P. solmsianum seedlings contain the phenylpropanoid dillapiole. Piper regnellii and P. hemmendorffii produce another phenylpropanoid, apiol, while isoasarone is found in P. caldense. Piper richadiaefolium and P. permucronatum contain dibenzylbutyrolactones lignans or flavonoids in adult leaves. Seedlings of P. richardiaefolium produce multiple amides, while P. permucronatum seedlings contain a new long chain ester. Piper tuberculatum, P. reticulatum and P. amalago produce amides, and their chemistry changes less during ontogeny. The chemical variation we documented opens questions about changes in herbivore pressure across ontogeny.