Researchers at the IPB have recently elucidated new molecular processes of flower development in tomato plants, giving us a better understanding of how seeds develop in these plants. “A lot of data from the work of two of my PhD students went into this extensive study, which we have now published in Plant Cell (Schubert et al. 2019),” said Prof. Bettina Hause, IPB research group leader and head of the study. “And we are very pleased that our publication was even chosen as the cover story.” One of her photos of a tomato flower now adorns the cover of the current May issue of the renowned journal (Fig. 1).
Flower development is controlled by the interaction of different plant hormones including jasmonates. For some time now, research has been carried out on mutant plants with impaired jasmonate perception. In the model plant Arabidopsis thaliana, these jasmonate-insensitive mutants exhibit sterility due to defects in male flower parts. In contrast, the same mutation in tomato plants leads to sterility due to misdevelopments in the female flower parts such as the ovules in the ovary (Fig. 2). As a result, the mutants carry seedless tomato fruits. Bettina Hause and her team now investigated the underlying molecular causes to seedless tomato fruits in jasmonate-insensitive mutants.
In order to elucidate the processes in detail, the scientists first prepared the ovules from wild type and jasmonate-insensitive mutants of different developmental stages and subjected it these to transcript-profiling for measuring and comparing gene activity. They found that differential gene expression was most pronounced at an intermediate stage of ovule development. They observed, that at that particular stage, many genes remained inactive in jasmonate-insensitive plants. Interestingly, at the same developmental stage, they observed a maximum jasmonate content in ovules of wild type plants but not in jasmonate-insensitive mutants. Everything here pointed to jasmonate-controlled gene activities in ovules, which were apparently disturbed in the jasmonate-insensitive mutant.
Next, the molecular regulators crucial for ovule development had to be fished from the large number of differentially activated genes. Bettina Hause and her team succeeded in identifying the transcription factor MYB21 as such a central regulator. For Arabidopsis, MYB21 had earlier been shown to control the development of male flower parts and to be activated by jasmonate. Schubert et al. provide thorough evidence that MYB21 also acts as a transcription factor in the jasmonate signalling pathway of tomato plants, but controls the development of the female flower parts, i.e. the seed production.
Furthermore, in jasmonate-insensitive mutants, the researchers observed signs of premature degradation of a tissue layer in the ovary - a process that normally only occurs after fertilisation. With additional transcript profiling experiments they demonstrated that other hormone signalling pathways are controlled by MYB21. Consequently, they hypothesize that the misregulation of these signalling pathways is responsible for the premature degradation processes in ovules when jasmonate signaling is impaired, thus ultimately resulting in seedless fruits. With their publication, Hause and her team present a model of the function of the central MYB21 transcription factor in the jasmonate-regulated flower development of tomato plants (Fig. 3).
Original publication:
Tomato MYB21 Acts in Ovules to Mediate Jasmonate-Regulated Fertility.
Ramona Schubert, Susanne Dobritzsch, Cornelia Gruber, Gerd Hause, Benedikt Athmer, Tom Schreiber, Sylvestre Marillonnet, Yoshihiro Okabe, Hiroshi Ezura, Ivan F. Acosta, Danuse Tarkowska, Bettina Hause. The Plant Cell May 2019, 31 (5) 1043-1062; DOI: 10.1105/tpc.18.00978
Cover: www.plantcell.org/content/31/5.cover.pdf
About the Cover: http://www.plantcell.org/content/31/5.cover-expansion
Plantae first author feature Ramona Schubert: plantae.org/research/r-the-plant-cell/recognizing-plant-cell-first-authors-ramona-schubert/
