Expression and function of the bHLH genes ALCATRAZ and SPATULA in selected Solanaceae species

The genetic mechanisms underlying fruit development have been identified in Arabidopsis and have been comparatively studied in tomato as a representative of fleshy fruits. However, comparative expression and functional analyses on the bHLH genes downstream the genetic network, ALCATRAZ (ALC) and SPATULA (SPT), which are involved in the formation of the dehiscence zone in Arabidopsis, have not been functionally studied in the Solanaceae. Here, we perform detailed expression and functional studies of ALC/SPT homologs in Nicotiana obtusifolia with capsules, and in Capsicum annuum and Solanum lycopersicum with berries. In Solanaceae, ALC and SPT genes are expressed in leaves, and all floral organs, especially in petal margins, stamens and carpels; however, their expression changes during fruit maturation according to the fruit type. Functional analyses show that downregulation of ALC/SPT genes does not have an effect on gynoecium patterning; however, they have acquired opposite roles in petal expansion and have been co‐opted in leaf pigmentation in Solanaceae. In addition, ALC/SPT genes repress lignification in time and space during fruit development in Solanaceae. Altogether, some roles of ALC and SPT genes are different between Brassicaceae and Solanaceae; while the paralogs have undergone some subfunctionalization in the former they are mostly redundant in the latter.     

Genetic control of male fertility in Arabidopsis thaliana: structural analysis of premeiotic developmental mutants

We have taken a mutational approach to identify genes important for male fertility in Arabidopsis thaliana and have isolated a number of nuclear male/ sterile mutants in which vegetative growth and female fertility are not altered. Here we describe detailed developmental analyses of four mutants, each of which defines a complementation group and has a distinct developmental end point. All four mutants represent premeiotic developmental lesions. In ms3, tapetum and middle layer hypertrophy result in the degeneration of microsporocytes. In ms4, microspore dyads persist for most of anther development as a result of impaired meiotic division. In ms5, degeneration occurs in all anther cells at an early stage of development. In ms15, both the tapetum and microsporocytes degenerate early in anther development. Each of these mutants had shorter filaments and a greater number of inflorescences than congenic male-fertile plants. The differences in the developmental phenotypes of these mutants, together with the non-allelic nature of the mutations indicate that four different genes important for pollen development, have been identified.     

Epidermal jasmonate perception is sufficient for all aspects of jasmonate‐mediated male fertility in Arabidopsis

Jasmonate (JA) signaling is essential for several environmental responses and reproductive development in many plant species. In Arabidopsis thaliana, the most obvious phenotype of JA biosynthetic and perception mutants is profound sporophytic male sterility characterized by failure of stamen filament elongation, severe delay of anther dehiscence and pollen inviability. The site of action of JA in the context of reproductive development has been discussed, but the ideas have not been tested experimentally. To this end we used targeted expression of a COI1‐YFP transgene in the coi1‐1 mutant background. As COI1 is an essential component of the JA co‐receptor complex, the null coi1‐1 mutant is male sterile due to lack of JA perception. We show that expression of COI1‐YFP in the epidermis of the stamen filament and anther in coi1 mutant plants is sufficient to rescue filament elongation, anther dehiscence and pollen viability. In contrast, filament expression alone or expression in the tapetum do not restore dehiscence and pollen viability. These results demonstrate that epidermal JA perception is sufficient for anther function and pollen viability, and suggest the presence of a JA‐dependent non‐autonomous signal produced in the anther epidermis to synchronize both anther dehiscence and pollen maturation.