SUMMARYMembers of the CENTRORADIALIS (CEN)/TERMINAL FLOWER 1 (TFL1) subfamily control shoot meristem identity, and loss-of-function mutations in both monopodial and sympodial herbaceous plants result in dramatic changes in plant architecture. We studied the degree of conservation between herbaceous and woody perennial plants in shoot system regulation by overexpression and RNA interference (RNAi)-mediated suppression of poplar orthologs of CEN, and the related gene MOTHER OF FT AND TFL 1 (MFT). Field study of transgenic poplars (Populus spp.) for over 6 years showed that downregulation of PopCEN1 and its close paralog, PopCEN2, accelerated the onset of mature tree characteristics, including age of first flowering, number of inflorescences and proportion of short shoots. Surprisingly, terminal vegetative meristems remained indeterminate in PopCEN1-RNAi trees, suggesting the possibility that florigen signals are transported to axillary mersitems rather than the shoot apex. However, the axillary inflorescences (catkins) of PopCEN1-RNAi trees contained fewer flowers than did wild-type catkins, suggesting a possible role in maintaining the indeterminacy of the inflorescence apex. Expression of PopCEN1 was significantly correlated with delayed spring bud flush in multiple years, and in controlled environment experiments, 35S::PopCEN1 and RNAi transgenics required different chilling times to release dormancy. Considered together, these results indicate that PopCEN1/PopCEN2 help to integrate shoot developmental transitions that recur during each seasonal cycle with the age-related changes that occur over years of growth.

Multiple factors, including the MADS-domain proteins AGAMOUS-LIKE15 (AGL15) and AGL18, contribute to the regulation of the transition from vegetative to reproductive growth. AGL15 and AGL18 were previously shown to act redundantly as floral repressors and upstream of FLOWERING LOCUS T (FT) in Arabidopsis (Arabidopsis thaliana). A series of genetic and molecular experiments, primarily focused on AGL15, was performed to more clearly define their role. agl15 agl18 mutations fail to suppress ft mutations but show additive interactions with short vegetative phase (svp) mutations in ft and suppressor of constans1 (soc1) backgrounds. Chromatin immunoprecipitation analyses with AGL15-specific antibodies indicate that AGL15 binds directly to the FT locus at sites that partially overlap those bound by SVP and FLOWERING LOCUS C. In addition, expression of AGL15 in the phloem effectively restores wild-type flowering times in agl15 agl18 mutants. When agl15 agl18 mutations are combined with agl24 svp mutations, the plants show upward curling of rosette and cauline leaves, in addition to early flowering. The change in leaf morphology is associated with elevated levels of FT and ectopic expression of SEPALLATA3 (SEP3), leading to ectopic expression of floral genes. Leaf curling is suppressed by sep3 and ft mutations and enhanced by soc1 mutations. Thus, AGL15 and AGL18, along with SVP and AGL24, are necessary to block initiation of floral programs in vegetative organs.Appropriate timing of the shift from vegetative to reproductive growth is an important determinant of plant fitness. The time at which a plant flowers is determined through integration of signals reflecting extrinsic and intrinsic conditions, such as photoperiod, the duration of cold, plant health, and age (for review, see Amasino, 2010). One of the most important pathways regulating the timing of the floral transition is the photoperiod pathway (for review, see Imaizumi and Kay, 2006). Under long-day (LD) inductive conditions in Arabidopsis (Arabidopsis thaliana), photoperiod pathway components act to promote flowering by inducing CONSTANS (CO) and downstream genes. The floral integrator FLOWER-ING LOCUS T (FT) is a major target of multiple flowering pathways and the photoperiod pathway in particular. It is directly activated by CO (Samach et al., 2000). Under LD conditions, the peak of CO expression is coincident with the presence of light, and CO activates FT expression in the leaf vascular system (Yanovsky and Kay, 2003). FT travels through the phloem to the shoot apex (Corbesier et al., 2007), where, together with FLOWER-ING LOCUS D (Abe et al., 2005;Wigge et al., 2005), it activates APETALA1 (AP1) and other floral meristem identity genes, starting the flowering process. Other flowering time pathways converge on FT and/or directly impact gene expression in the meristem. The changes in gene expression that accompany the floral transition must be rapid, robust, largely irreversible, and strictly controlled spatially. This is achieved through positive feedforwa...

Premise of the StudySimple sequence repeat (SSR) and expressed sequence tag (EST)–SSR markers were developed as tools for marker‐assisted selection of Chamaecyparis formosensis and for the molecular differentiation of cypress species.Methods and ResultsBased on the SSR‐enriched genomic libraries and transcriptome data of C. formosensis, 300 primer pairs were selected for initial confirmation, of which 19 polymorphic SSR and eight polymorphic EST‐SSR loci were chosen after testing in 92 individuals. The number of alleles observed for these 27 loci ranged from one to 17. The levels of observed and expected heterozygosity ranged from 0.000 to 1.000 and from 0.000 to 0.903, respectively. Most markers also amplified in C. obtusa var. formosana.ConclusionsThe developed SSR and EST‐SSR sequences are the first reported markers specific to C. formosensis. These markers will be useful for individual identification of C. formosensis and to distinguish cypress species such as C. obtusa var. formosana.

The objective of this research was to use random amplified polymorphic DNA (RAPD) and isozyme analysis to investigate genetic variation in narrowly distributed populations of Amentotaxus formosana Li. A total of 20 loci from 10 enzyme systems were analysed in 50 individual trees from each of the two natural populations. No isozyme variation was observed in the Tsatsayalai population. Phosphoglucose isomerase (Pgi-1) was the only polymorphic enzyme in the Tawu population, giving 5 per cent polymorphic loci with 0.008 expected heterozygosity. No genetic distance was found between these two populations using isozymes. Amentotaxus formosana demonstrated a high proportion of monomorphic RAPD fragments, about 79 per cent, for 20 arbitrary oligonucleotide primers. High similarity (0.994) was found between the Tawu and Tsatsayalai populations. RAPD markers provided further confirmation of the low levels of genetic variation in A. forinosana detected by isozyme analysis. The value of isozyme analysis was emphasized by the finding of the rare allele, Pgi-la, which was present only in the Tawu population. Based on the analysis of 110 individuals, representing 16 per cent of a native population, it was found that the younger tree category had a higher frequency of Pgi-la (0.125) than the older tree category (0.053), resulting in an expected heterozygosity of 0.250 and 0.105, respectively. It was inferred that the appearance of the Pgi-la allele could be the result of a mutation in the Tawu population and that selection is acting directly upon trees carrying this allele.