No abstract

We investigated 29 natural populations of Cryptomeria japonica using 148 cleaved amplified polymorphic sequence markers to elucidate their genetic structure and identify candidate adaptive genes of this species. In accordance with the inferred evolutionary history of the species during and after the last glacial episode, the genetic diversity was higher in western populations than in northern populations. The results of phylogenetic and genetic structure analyses suggest that populations of the two main varieties of the species have clearly diverged from each other and that two of the examined loci are strongly associated with the differentiation between the two varieties. Using a coalescent simulation based on F ST and H e values, we detected five genes that had higher, and two that had lower, values than the respective 99% confidence intervals (C.I.s) that are theoretically expected intervals under a neutral infinite-island model. We also detected 13 outlier loci using a coalescent simulation based on the assumption that the 2 varieties originated from the splitting of an ancestral population. Four of these loci were detected by both methods, two of which were detected in a genetic structure analysis as loci associated with differentiation between the two varieties of the species, and are strong candidates for genes that have been subject to selection.

Elucidating the physiological mechanisms of the irregular yet concerted flowering rhythm of mass flowering tree species in the tropics requires long-term monitoring of flowering phenology, exogenous and endogenous environmental factors, as well as identifying interactions and dependencies among these factors. To investigate the proximate factors for floral initiation of mast seeding trees in the tropics, we monitored the expression dynamics of two key flowering genes, meteorological conditions and endogenous resources over two flowering events of Shorea curtisii and Shorea leprosula in the Malay Peninsula. Comparisons of expression dynamics of genes studied indicated functional conservation of FLOWERING LOCUS T (FT) and LEAFY (LFY) in Shorea. The genes were highly expressed at least 1 month before anthesis for both species. A mathematical model considering the synergistic effect of cool temperature and drought on activation of the flowering gene was successful in predicting the observed gene expression patterns. Requirement of both cool temperature and drought for floral transition suggested by the model implies that flowering phenologies of these species are sensitive to climate change. Our molecular phenology approach in the tropics sheds light on the conserved role of flowering genes in plants inhabiting different climate zones and can be widely applied to dissect the flowering processes in other plant species.

Pinus species have three differently inherited genomes: paternal chloroplast, maternal mitochondrial, and biparental nuclear. Our previous study on the hybrid zones between alpine Pinus pumila and montane to subalpine P. parviflora var. pentaphylla demonstrated contrasting patterns of introgression of two cytoplasmic genomes, i.e., the paternal cpDNA flowed from P. parviflora var. pentaphylla to P. pumila, and the maternal mtDNA flowed in the reverse direction. In the present study, we developed codominant nuclear DNA markers diagnostic or mostly diagnostic for each parental species by single-strand conformation polymorphism (SSCP) of polymerase chain reaction (PCR) products, using expressed sequence tag (EST) primers of Pinus taeda. To describe the introgressive patterns of the nuclear genes, the molecular hybrid index (MHI) showing the overall proportion of alleles inferred to be derived from P. pumila was determined for each plant collected in hybrid zones on Mt. Asahidake and Mt. Higashiazuma, Japan. At Mt. Asahidake, the MHI values changed clinally according to the altitudes at which the plants were collected. However, at Mt. Higashiazuma, there was a gap in the MHI values between the plants above and below the Abies and Tsuga forest zone (alt. 1800-1900 m). This suggested that the zone plays a role in creating an effective barrier to gene flow in the hybrid zone.