Mutation in Arabidopsis MOR1 Gene Impairs Endocytosis in Stamen Filament Cells and Results in Anther Indehiscence

Anther dehiscence is a crucial step for pollen grain release and male fertility. Filaments, which transport water, nutrients and hormones to the anthers, are important for anther dehiscence. In this study, we characterized the Arabidopsis microtubule organization 1 (MOR1) gene that involves in the filament functions and plays important roles in anther dehiscence. The Arabidopsis microtubule organization 1-1 (mor1-1) mutant exhibited an anther indehiscence phenotype at 24°C. Such the defect in anther dehiscence did not occur at a lower temperature (19°C). Further analysis indicated that both the cortical microtubule (CMT) organization and plasma membrane homeostasis were drastically impaired and disturbed in mor1-1 filament cells under the growth conditions of 24°C. Transmission electron microscopy (TEM) and FM4-64 up-take assays showed that endocytosis process in the mor1-1 filament cells were disrupted at 24°C. Furthermore, the cortical-associated RFP tagged clathrin light chain (CLC-RFP) foci were reduced in the mor1-1 filament cells. These results suggested that the MOR1-mediated CMT organization is important for clathrin-mediated endocytosis in the filament cells, and critical for anther dehiscence in thermosensitivity.

Developmental and molecular characterization of novel staminodes in Aquilegia

Background and Aims The ranunculid model system Aquilegia is notable for the presence of a fifth type of floral organ, the staminode, which appears to be the result of sterilization and modification of the two innermost whorls of stamens. Previous studies have found that the genetic basis for the identity of this new organ is the result of sub- and neofunctionalization of floral organ identity gene paralogues; however, we do not know the extent of developmental and molecular divergence between stamens and staminodes. Methods We used histological techniques to describe the development of the Aquilegia coerulea ‘Origami’ staminode relative to the stamen filament. These results have been compared with four other Aquilegia species and the closely related genera Urophysa and Semiaquilegia. As a complement, RNA sequencing has been conducted at two developmental stages to investigate the molecular divergence of the stamen filaments and staminodes in A. coerulea ‘Origami’. Key Results Our developmental study has revealed novel features of staminode development, most notably a physical interaction along the lateral margin of adjacent organs that appears to mediate their adhesion. In addition, patterns of abaxial/adaxial differentiation are observed in staminodes but not stamen filaments, including asymmetric lignification of the adaxial epidermis in the staminodes. The comparative transcriptomics are consistent with the observed lignification of staminodes and indicate that stamen filaments are radialized due to overexpression of adaxial identity, while the staminodes are expanded due to the balanced presence of abaxial identity. Conclusions These findings suggest a model in which the novel staminode identity programme interacts with the abaxial/adaxial identity pathways to produce two whorls of laterally expanded organs that are highly differentiated along their abaxial/adaxial axis. While the ecological function of Aquilegia staminodes remains to be determined, these data are consistent with a role in protecting the early carpels from herbivory and/or pathogens.

The Role of Water in Fast Plant Movements

Plants moved onto land ∼450 million years ago and faced their biggest challenge: living in a dry environment. Over the millennia plants have become masters of regulating water flow and the toolkit they have developed has been co-opted to effect rapid movements. Since plants are rooted, these fast movements are used to disperse reproductive propagules including spores, pollen, and seeds. We compare five plants to demonstrate three ways, used alone or in combination, that water powers rapid movements: the direct capture of the kinetic energy of a falling raindrop propels gemmae from the splash cups of the liverwort, Marchantia; the loss of water powers the explosive dispersal of the spores of Sphagnum moss; the alternate loss and gain of water in the bilayer of the elaters of Equisetum drive the walk, jump, and glide of spores; the gain of water in the inner layer of the arils of Oxalis drive the eversion of the aril that jettisons seeds from the capsule; and the buildup of turgor pressure in the petals and stamens of bunchberry dogwood (Cornus canadensis) explosively propels pollen. Each method is accompanied by morphological features, which facilitate water movement as a power source. The urn shaped splash cups of Marchantia allow dispersal of gemmae by multiple splashes. The air gun design of Sphagnum capsules results in a symmetrical impulse creating a vortex ring of spores. The elaters of Equisetum can unfurl while they are dropping from the plant, so that they capture updrafts and glide to new sites. The arils of Oxalis are designed like miniature toy “poppers.” Finally, in bunchberry, the softening of stamen filament tissue where it attaches to the anther allows them to function as miniature hinged catapults or trebuchets.