Evolutionary developmental genetics of fruit opening in Brassicaceae
Evolution and Systematics of Plants and Fungi
Plant Physiology
Final Report Abstract
Dehiscent fruits crack open and shed their seeds into the environment when the fruit is ripe; indehiscent fruits do not crack open and hence retain their seeds after maturation. While Lepidium campestre has dehiscent fruits and thus displays the ancestral state of the cabbage family, the closely related Lepidium appelianum develops indehiscent fruits. During the course of the project we wanted to clarify the molecular mechanisms underlying the evolutionary transition from dehiscent to indehiscent fruits as represented by these two species. In the first phase of the project we have shown that in the dehiscent fruits of L. campestre all four valve margin identity genes, that is SHP1, SHP2, IND and ALC, are expressed in the dehiscence zone but that such expression patterns at the valve/replum border are absent from L. appelianum indehiscent fruits. These data strongly suggest that a local reduction in valve margin identity gene expression was involved in the evolutionary transition from dehiscent to indehiscent fruits in Lepidium. However, we did not find evidence that a mutation at these loci was causally involved in the changes in the expression patterns. We hence hypothesized that a transcription factor that coordinately controls the expression of these genes is mutated in L. appelianum. Based on expression studies we hypothesized that the increased expression level of the negative upstream regulator AP2 is responsible for the loss of dehiscence zone identity gene expression and thus the indehiscence of L. appelianum fruits. However, expression studies in the second phase of the project did not corroborate previous findings that AP2 is more stongly expressed in L. appelianum than in L. campestre fruits. Ectopic overexpression of AP2 in transgenic Arabidopsis thaliana plants as well as knockout of the AP2 gene in L. campestre by CRISPR-Cas9 led to diverse mutant phenotypes. However, none of our observations made an involvement of the AP2 gene in fruit dehiscence appear likely, even though they also cannot completely rule out such a scenario so far. In an additional approach we sequenced the transcriptomes and small RNAs of floral buds, flowers and fruits of L. campestre and L. appelianum, and analyzed differentially expressed genes. This way we identified the transcription factors BRANCHED1 and TCP4, as well as the microRNA miR166 as candidates involved in the evolutionary transition from dehiscent to indehiscent fruits in Lepidium. However, future work is required to experimentally test this hypothesis, and to determine as to whether any of the loci encoding these gene products contain a causal mutation for fruit dehiscence in Lepidium.
Publications
- (2000) Plant biology: shattering developments. Nature 404, 711-713
Theißen G
(See online at https://doi.org/10.1038/35008171) - (2008) Tutti Frutti in Lepidium — Comparative analysis of fruit dehiscence/indehiscence in Brassicaceae. South African Journal of Botany 74, 373-374
Mummenhoff K, Theißen G, Mühlhausen A
(See online at https://doi.org/10.1016/j.sajb.2008.01.086) - (2009) Lepidium as a model system for studying the evolution of fruit development in Brassicaceae. J. Exp. Bot. 60, 1503–1513
Mummenhoff K, Polster A, Mühlhausen A, Theißen G
(See online at https://doi.org/10.1093/jxb/ern304) - (2010) Evolution of fruit dehiscence in Brassicaceae – examples from Aethionema and Lepidium. Acta Hort. (ISHS) 867, 207-219
Mühlhausen A, Polster A, Theißen G, Mummenhoff K
(See online at https://doi.org/10.17660/ActaHortic.2010.867.25) - (2013) Conservation of fruit dehiscence pathways between Lepidium campestre and Arabidopsis thaliana sheds light on the regulation of INDEHISCENT. Plant J. 76, 545-556
Lenser T, Theißen G
(See online at https://doi.org/10.1111/tpj.12321) - (2013) Evidence that an evolutionary transition from dehiscent to indehiscent fruits in Lepidium (Brassicaceae) was caused by a change in the control of valve margin identity genes. Plant J. 73, 824-835
Mühlhausen A, Lenser T, Mummenhoff K, Theißen G
(See online at https://doi.org/10.1111/tpj.12079) - (2013) Molecular mechanisms involved in convergent crop domestication. Trends Plant. Sci. 18, 704-714
Lenser T, Theißen G
(See online at https://doi.org/10.1016/j.tplants.2013.08.007) - (2014) Floral dip transformation in Lepidium campestre. bio-protocol 4(15), e1201
Lenser T, Theißen G
(See online at https://doi.org/10.21769/BioProtoc.1201) - (2021) Comparative transcriptomics identifies the transcription factors BRANCHED1 and TCP4, as well as the microRNA miR166 as candidate genes involved in the evolutionary transition from dehiscent to indehiscent fruits in Lepidium (Brassicaceae). bioRxiv
Gramzow, L., Klupsch K, Fernández Pozo N, Hölzer M, Marz M, Rensing SA, Theißen G
(See online at https://doi.org/10.1101/2021.10.29.466389) - (2020) Morphologically and physiologically diverse fruits of two Lepidium species differ in allocation of glucosinolates into immature and mature seed and pericarp. PLoS ONE 15(8), e0227528
Mohammed S, Bhattacharya S, Gesing MA, Klupsch K, Theißen G, Mummenhoff K, Müller C
(See online at https://doi.org/10.1371/journal.pone.0227528)
