Genomes tell tales of spores versus seeds.

Genomes from ferns and a cycad reveal deep roots of plant reproduction.

Height increment of Cycas micronesica informs conservation decisions.

Growth dynamics of pachycaulous stems of arborescent cycad plants are not well understood, and most observations have been made in cultivated garden plants. We studied Cycas micronesica plants in Guam, Tinian, and Yap to understand the influences of geography, plant size, sex, and herbivory on stem growth. We also determined the changes in demography of Guam's population after 15 years of damage by non-native insect herbivores. The height increment (HI) was similar for plants within the height range from 100 cm to more than 600 cm, so the relative growth rate declined with height. Female tree HI was 68% of male tree HI, and Yap tree HI was 87% of Guam tree HI. Chronic herbivory by non-native insect herbivores caused a mean 44% decline in HI. Plants in managed gardens grew more rapidly than plants in a wild habitat. The HI was used to estimate that Guam has experienced a complete loss of ≈70 y of demographic depth resulting from the selective mortality of small plants since 2005. When future conservation interventions successfully mitigate the ubiquitous biological threats, our HI may be useful for empirically quantifying recovery of plant health.

Middle-Upper Pleistocene climate changes shaped the divergence and demography of Cycas guizhouensis (Cycadaceae): Evidence from DNA sequences and microsatellite markers.

Climatic oscillations in the Pleistocene have had profound effects on the demography and genetic diversity of many extant species. Cycas guizhouensis Lan &R.F. Zou is an endemic and endangered species in Southwest China that is primarily distributed along the valleys of the Nanpan River. In this study, we used four chloroplast DNAs (cpDNA), three nuclear genes (nDNA) and 13 microsatellite (SSR) loci to investigate the genetic structure, divergence time and demographic history of 11 populations of C. guizhouensis. High genetic diversity and high levels of genetic differentiation among the populations were observed. Two evolutionary units were revealed based on network and Structure analysis. The divergence time estimations suggested that haplotypes of C. guizhouensis were diverged during the Middle-Upper Pleistocene. Additionally, the demographic histories deduced from different DNA sequences were discordant, but overall indicated that C. guizhouensis had experienced a recent population expansion during the post-glacial period. Microsatellite data revealed that there was a contraction in effective population size in the past. These genetic features allow conservation measures to be taken to ensure the protection of this endangered species from extinction.

Two distinct plant respiratory physiotypes might exist which correspond to fast-growing and slow-growing species.

The origin of the carbon atoms in CO2 respired by leaves in the dark of several plant species has been studied using 13C/12C stable isotopes. This study was conducted using an open gas exchange system for isotope labeling that was coupled to an elemental analyzer and further linked to an isotope ratio mass spectrometer (EA-IRMS) or coupled to a gas chromatography-combustion-isotope ratio mass spectrometer (GC-C-IRMS). We demonstrate here that the carbon, which is recently assimilated during photosynthesis, accounts for nearly ca. 50% of the carbon in the CO2 lost through dark respiration (Rd) after illumination in fast-growing and cultivated plants and trees and, accounts for only ca. 10% in slow-growing plants. Moreover, our study shows that fast-growing plants, which had the largest percentages of newly fixed carbon of leaf-respired CO2, were also those with the largest shoot/root ratios, whereas slow-growing plants showed the lowest shoot/root values.

Cone thermogenesis and its limits in the tropical Cycas micronesica (Cycadaceae): association with cone growth, dehiscence, and post-dehiscence phases.

PREMISE OF THE STUDY: Thermogenesis is a prominent pollination-related feature of cycad cones and is generally assumed to play a role in pollination. Although typically studied just before, during, and immediately after the cones' pollination phase, thermogenesis may be present in other cone developmental phases. • METHODS: We assayed thermogenesis in Cycas micronesica, Guam's endangered cycad, over successive cone developmental phases by measuring temperatures in shaded and unshaded in situ cones for up to 7 wk. We also studied the effect of ambient conditions on cone thermogenesis in laboratory experiments and estimated the cones' metabolic heating rates. • KEY RESULTS: Pollen cones exhibit a continuous, but small, metabolically generated thermogenesis for multiple weeks, including a single thermogenic peak temperature greater than peak ambient each day. The magnitudes of those daily peak temperature elevations above ambient reach maxima twice during cone development: a few days before dehiscence and approximately 1 wk post-dehiscence. Excised cones in dark, fixed temperature environments generated multiple thermogenic events (∼24 h period) over ∼10 d. Cones appear to initiate a protective temperature regulatory response at temperatures ≥∼38°C. • CONCLUSIONS: Cycas micronesica pollen cones exhibit several thermogenic attributes not reported in other cycads, including continuous thermogenesis for many weeks. These cones grow in a hot tropical environment that likely confines their metabolically generated temperature increases to a small thermogenic window beyond which they encounter heat stress. These findings suggest the presence of thermogenic functions not strictly related to pollination and a potential vulnerability to warming climates.

Cycas micronesica (Cycadales) plants devoid of endophytic cyanobacteria increase in beta-methylamino-L-alanine.

Cycads are among the most ancient of extant Spermatophytes, and are known for their pharmacologically active compounds. beta-methylamino-l-alanine (BMAA) is one metabolite that been implicated as causal of human neurodegenerative diseases in Guam. We grew Cycas micronesica seedlings without endophytic cyanobacteria symbiosis, and quantified initial and ending BMAA in various plant tissues. BMAA increased 79% during nine months of seedling growth, and root tissue contained 75% of the ultimate BMAA pool. Endophytic cyanobacteria symbionts were not the source of BMAA increase in these seedlings, which contradicts previously reported claims that biosynthesis of this toxin by cyanobacteria initiates its accumulation in the Guam environment. The preferential loading of root tissue with BMAA does not support earlier reports that this toxin serves a defensive role against herbivory of leaf or seed tissues. The long history of conflicting results in Guam's cycad toxin research continues, and recent developments underscore the sense of urgency in continued research as this endangered cycad population approaches extirpation from the island.

[Age estimation and age structure of Cycas fairylakea population in Shenzhen City].

Based on the structural characteristics of Cycas trunk, including vegetative leaf base scars, sporophyll concave rings, and average occurrence probabilities of vegetative leaf and sporophyll, a method for the age estimation of Cycas fairylakea population was developed, and the age of each individual was calculated. Three approaches, i.e., age structure diagram, age distribution curve and curve estimation were used to study the age structure of C. fairylakea population at genet and clone population levels. The age structure diagram showed that the clone population of C. fairylakea was stable, but the genet population was in declining. However, both of the clone and genet populations were in declining when using the other two approaches. It was considered that the C. fairylakea population was in declining, and needed an urgent protection.

Conservation of class C function of floral organ development during 300 million years of evolution from gymnosperms to angiosperms.

Flower development in angiosperms is regulated by the family of MADS-box transcription factors. MADS-box genes have also been reported from gymnosperms, another major group of seed plants. AGAMOUS (AG) is the class C MADS-box floral organ identity gene controlling the stamen and carpel development in Arabidopsis. We report the characterization of an ortholog of the AG gene, named Cycas AGAMOUS (CyAG), from the primitive gymnosperm Cycas edentata. The expression pattern of CyAG in Cycas parallels that of AG in Arabidopsis. Additionally, the gene structure, including the number and location of the introns, is conserved in CyAG and other AG orthologs known. Most importantly, functional analysis shows that CyAG driven by the AG promoter can rescue the loss-of-function ag mutant of Arabidopsis. However, the ectopic expression of CyAG in ag mutant Arabidopsis cannot produce the carpeloid and stamenoid organs in the first and second whorls, although the stamen and carpel are rescued in the third and fourth whorls of the transformants. These observations show that the molecular mechanism of class C function controlling reproductive organ identity (stamen and carpel of angiosperms or microsporophyll and megasporophyll of gymnosperms) arose before the divergence of angiosperms and gymnosperms, and has been conserved during 300 million years of evolution thereafter.