Three new species of Iodosphaeria (Xylariomycetidae): I. chiayiensis, I. jinghongensis and I. thailandica

Three fungal specimens (two sexual and one asexual) were collected during fieldwork conducted in China, Taiwan and Thailand. Both sexual morphs share superficial, black ascomata surrounded by flexuous setae; 8-spored, unitunicate, cylindrical asci, with J+, apical ring, and ellipsoidal to allantoid, aseptate, guttulate ascospores. The asexual morph has ceratosporium-like conidia arising from aerial hyphae with a single arm and are usually attached or with 2–3 arms, brown, often with a subglobose to conical cell at the point of attachment. Morphological examinations and phylogenetic analyses of a combined LSU-ITS dataset via maximum likelihood and Bayesian analyses indicated that these three collections were new species. Iodosphaeria chiayiensis (sexual morph), I. thailandica (sexual morph) and I. jinghongensis (asexual morph) are therefore introduced as new species in this study. Iodosphaeria chiayiensis has small, hyaline and ellipsoidal to allantoid ascospores, while I. thailandica has large ascomata, cylindrical to allantoid asci and hyaline to pale brown ascospores.

Cortical Microtubule Organization during Petal Morphogenesis in Arabidopsis

Cortical microtubules guide the direction and deposition of cellulose microfibrils to build the cell wall, which in turn influences cell expansion and plant morphogenesis. In the model plant Arabidopsis thaliana (Arabidopsis), petal is a relatively simple organ that contains distinct epidermal cells, such as specialized conical cells in the adaxial epidermis and relatively flat cells with several lobes in the abaxial epidermis. In the past two decades, the Arabidopsis petal has become a model experimental system for studying cell expansion and organ morphogenesis, because petals are dispensable for plant growth and reproduction. Recent advances have expanded the role of microtubule organization in modulating petal anisotropic shape formation and conical cell shaping during petal morphogenesis. Here, we summarize recent studies showing that in Arabidopsis, several genes, such as SPIKE1, Rho of plant (ROP) GTPases, and IPGA1, play critical roles in microtubule organization and cell expansion in the abaxial epidermis during petal morphogenesis. Moreover, we summarize the live-confocal imaging studies of Arabidopsis conical cells in the adaxial epidermis, which have emerged as a new cellular model. We discuss the microtubule organization pattern during conical cell shaping. Finally, we propose future directions regarding the study of petal morphogenesis and conical cell shaping.

The mechanics of cell fate determination in petals

The epidermal cells of petals of many species are specialized, having a pronounced conical shape. A transcription factor, MIXTA, is required for the formation of conical cells in Antirrhinum majus ; in shoot epidermal cells of several species, expression of this gene is necessary and sufficient to promote conical cell formation. Ectopic expression has also shown MIXTA to be able to promote the formation of multicellular trichomes, indicating that conical cells and multicellular trichomes share elements of a common developmental pathway. Formation of conical cells or trichomes is also mutually exclusive with stomatal formation. In Antirrhinum , MIXTA normally only promotes conical cell formation on the inner epidermal layer of the petals. Its restricted action in cell fate determination results from its specific expression pattern. Expression of MIXTA , in turn, requires the activity of B–function genes, and biochemical evidence suggests that the products of DEFICIENS , GLOBOSA and SEPALLATA –related genes directly activate MIXTA expression late in petal development, after the completion of cell division in the petal epidermis. A MIXTA –like gene, AmMYBML1 , is also expressed in petals. AmMYBML1 expression is high early in petal development. This gene may direct the formation of trichomes in petals. In specifying the fates of different cell types in petals, regulatory genes like MIXTA may have been duplicated. Changes in the timing and spatial localization of expression then provides similar regulatory genes which specify different cell fates.