Lab of developmental genetics and evolution

    Our lab’s main research interest is on developmental genetic of flower morphogenesis and flower symmetry. Also, we have members working on genetic control of bulbil morphogenesis, heterophyly and flower sex determinacy. This is a research area currently very dominant in the field of modern biology (so called “Evo-Devo”). In addition, we are interested in molecular biogeography relationships of several East Asia plant species including several relic gymnosperm species. My researches therefore can be summarized into five main categories listed as below.

(1)     Genetic control of meristem commitement and flower reversion:

The induction of flowering is one of the most important developmental transitions for sexually reproducing angiosperms. However, flower reversion back to vegetative meristem development can be observed in some species under environmental conditions opposite to those that induce flowering. These reversions, although it is infrequent, can provide us an exciting opportunity to identify the genetic mechanism of meristem commitment and flower reversion in shoot apex (Fig.1).

The developmental mechanism of flower reversion is not fully understood. But most of the recent evidences in Arabidopsis indicate that those shoot apical meristem (SAM) maintenance genes are involved in this process.

Titanotrichum oldhamii (Gesneriaceae) has inflorescences bearing either showy yellow flowers or asexual bulbils and a reversal from flowering to asexual bulbiliferous shoots (newly formed shoots containing only vegetative bulbils meristems, Fig.2), occurs when plants are exposed under short-day (SD) conditions (Wang & Cronk 2003). Floral meristem identity gene LEAFY (LFY) and meristem regulatory gene WUSCHEL (WUS) are thought to be a major switch to promote flowering. They activate the expression of the homeotic gene AGAMOUS (AG). Another genes regulating vegetative meristem such as ASYMMETRIC LEAVES1 (AS1) thus can be turned on to initiate leaf primordia. AS1 is negatively regulated through a genetic interaction network of two SAM maintenance genes, SHOOTMERISTEMLESS (STM) and KNOTTED1 (KNAT1).

We therefore examined the LFY, STM, AS1 and KNAT1 expression domain within floral and vegetative meristem using RNA in-situ hybridization techniques (Fig. 3). In addition, overexpressing and silencing vectors has been constructed to study their function in proving their putative roles in meristem transition. The expected result of this project will certainly contribute to a better understanding of the evolution of flower reversion mechanism in two years time.

Based on this result, we are now interested in another bulbiliferous plant, Remusatia vivipara. With the help of a PhD student, Huang, Chi-Dong, we hope to figure out how bulbils develop and whether a similar genetic mechnism like Titanotrihchum has also been evolved in Remusatia (Fig. 4).

(2) developmental genetic mechanism of flower symmetry in relation to pollination

syndrome

The evolution of floral dorsi-ventral asymmetry (zygomorphy) has been well known in facilitating pollination specificity and speciation rate. Species with dorsiventral floral symmetry are thought to have evolved because of their adaptive advantage in facilitating pollinator visits. Flowers with dorsi-ventral symmetry have evolved independently in numerous lineages of angiosperms, such as Legume, Orchid and Labiates. Gesneriaceae species have ancestral zygomorphy yet reversion to actinomorphy is frequent in major clades. Studying closely related yet morphologically divergent lineages in Gesneriaceae provides an exciting opportunity to study the evolutionary developmental mechanism involved in floral symmetry, as the developmental genetics of the wild type and the peloric form can easily be compared in a related genetic backgrounds.

The peloric mutant arose during African violet (Saintpaulia ionantha) domestication and peloric Sinningia (garden gloxinia) from cultivation provides us a great opportunity to study the evolution and developmental mechanism about the conversion of flower symmetry. Natural reversals to actinomorphy, such as the Pyrenean paleoendemic species Ramonda myconi (L.) Schultz and a convergent monotypic species Conandron ramondioides Sieb. et Zucc. in Eastern Asia including Taiwan, are also promising examples indicating the developmental mechanism of floral symmetry can independently evolve in different lineages (Fig. 5).  

Researches in my laboratory are therefore focused on the evolution of floral symmetry genes and their function on flower symmetry in Gesneriaceae species. My main interest is in understanding the evolution and functions of Gesneriaceae flower symmetry genes CYCLOIDEA (CYC), RADIALIS (RAD) and DIVARICATA (DIV) with reference to their flower morphology (Fig. 6).

To further analyse the interactions of these floral symmetry genes, we conduct in-situ hybridisation analysis to localize the expression domain of these genes in floral meristem disections. In addition, each gene will be ectopically expressed in transgenic Arabidopsis to observe the phenotypic conversion. Ultimately we will use tobacco rattle virus to perform virus-induced gene silencing (VIGS) in Saintpaulia to confirm the function of these floral symmetry genes.

(3)   Biogeography of endemic East Asia plant species.

Many East-Asia endemic species have intriguing disjunctive distribution either jump from SW China to Taiwan and even to Japan. Taiwania cryptomerioides and Amentotaxus formosana are classical gymnosperm examples. Although either Taiwania cryptomerioides or Amentotaxus formosana have been separated from their SW China relative species for such a long historical time after glacier age, their morphology are remarkably similar in distant locations. We are therefore interested in study their genetic divergence among current distributions (SW China, Vietnam and Taiwan) using nuclear and chloroplast molecular markers. Hope we can figure out their current diversity center in suggestions to conservation.

More than that, we are also interested in genetic divergence of several endemic alpine species in Taiwan across Asia. Two current projects are in geneus Euphrasia (Scrophulariaceae) and Conandron ramoideas (Gesneriaceae). They have either Japan-Taiwan-China distribution type or rapid speciation in isolated mountain area. We currently apply nuclear developmental gene markers such as CYCLOIDEA to link their flower morpho type and species divergent rates. There is another joint project with Philipine’s botanist, Rosario Rubite, in resolving the rapid speciation of Begonia using molecular phylogenetic analysis. Together with all, we hope to better understand the species evolution pattern in these East-Asia species.

(4)   Heterophyly in water plants

Heterophyly refers to dimorphism of leaf development within one individual when subject to different environmental cues. Limnophila heterophylla is one example that its leaf shape can vary from linear tube form when submerged in water to lanceolate type after evolving above water. There is a growing evidence indicating plant hormone such as ethylene production and leaf developing genes such as KNOX are responsible for the development of leaf shape transition.

Currently my lab is collaborating with Dr. Michael Moeller’s group in Royal Botanic Garden Edinburgh of UK and Dr. Kanae Nishii’s lab in the University of Tokyo, Japan. We form this group aiming to study functions of KNOX family genes in regulating vegetative meristem formation and leaf development.

(5)     Flower development in monoecious Begonia natural variants

The evolution of flower sex is a major interest to many botanists. Monoecious species serve as good materials to study the transition of flower sex because they have flowers switching from/to male to/from female within the exact individual. Natural Begonia species are exciting examples as although they are monoecious, several mutant species containing only male or female flowers provide precious chances to study the developmental genetic of sex determination. We are now collaborating with Dr. Peng, Ching-I in Academia Sinica and experts in Royal Botanic Garden Edinburgh in searching the molecular genetic mechanism related to Begonia flower sex.

Opportunities for PhD students and research assistantship

Our lab now offers several PhD student positions and research assistant positions to international applicants. You are welcome to join us in exploring the world of developmental genetic of plant (Fig. 7). If you are interested in this, please email me your CV and publication lists with proper academic statement. Thanks!

Fig. 1 Flower reversions in Titanotrichum oldhamii. It has great range of variation in inflorescence. (See Wang & Cronk 2003)

Fig.2 Photos of flower and bulbil initiation and their micro structure under SEM (Wang & Cronk 2003)

Fig. 3. A trial RNA in-situ hybridization result of C-class gene during floral organ meristem formation.

Fig. 4 Left: Shoot apex dissection of Remusatia vivipara (note that heavily stained primordial at left is an emerging bulbil); Right: a line drawing of Remusatia vivipara and its bulbils (by Huang, Chi-Dung)

Fig. 5 Naturally occurring peloric “mutants” and closely related yet morphologically reverted lineages in Gesneriaceae provide an exciting opportunity to study the evolutionary developmental mechanism involved in floral symmetry. Species on the right are natural peloric and probably are examples of null mutant of CYCLOIDEA or RADIALIS. (See Wang & Cronk 2006a for details)

Fig. 6. The wild type (photo left) Saintpaulia (African Violet) flower and its peloric cultivar (photo right). The hypothesized genetic interactions among floral symmetry genes CYCLOIDEA (CYC), RADIALIS (RAD) and DIVARICATA (DIV) are indicated in diagram at right (See Wang & Cronk 2006b for details).

Fig. 7 Cover photo of Wang, C.-N et al. (2004b) Development Genes Evolution 214: 122-127. This photo shows the bulbil cluster of a rare plant in Taiwan (Titanotrichum oldhamii). The candidate gene (GFLO) expression is down-regulated in bulbil inflorescence.

Fig. 8 Use aniline blue to label pollen tubes in ovule fertilization process. From Wang et al. (2004d)