Lalatovic, K. | Search bioRxiv

bioRxiv2024

Long days induce adaptive secondary dormancy in seed of the Mediterranean plant Aethionema arabicum

Secondary dormancy is an adaptive trait that increases reproductive success by aligning seed germination with permissive conditions for seedling establishment. Aethionema arabicum is an annual plant and member of the Brassicaceae that grows in environments characterized by hot and dry summers. Aethionema arabicum seeds may germinate in early spring when seedling establishment is permissible. We demonstrate that long-day light regimes induce secondary dormancy in seed of Aethionema arabicum (CYP accession) repressing germination in summer when seedling establishment is riskier. Characterization of mutants screened for defective secondary dormancy demonstrated that RGL2 mediates repression of genes involved in GA signalling. Exposure to high temperature alleviates secondary dormancy, restoring germination potential. These data are consistent with the hypothesis that long-day-induced secondary dormancy and its alleviation by high temperatures, may be part of an adaptive response limiting germination to conditions permissive for seedling establishment in spring and autumn.

plant biology↗

bioRxiv2022

Phytochromes mediate germination inhibition under red, far-red, and white light in Aethionema arabicum

The view on the role of light during seed germination stems mainly from studies with Arabidopsis, where light is required to initiate this process. In contrast, white light is a strong inhibitor of germination in other plants, exemplified by accessions of Aethionema arabicum, another Brassicaceae. Their seeds respond to light with gene expression changes of key regulators converse to Arabidopsis, resulting in antipodal hormone regulation and prevention of germination. The photoreceptors involved in this process in A. arabicum were unknown. Screening the first mutant collection of A. arabicum, we identified koy-1, a mutant that lost light inhibition of germination, due to a deletion in the promoter of HEME OXYGENASE 1, the gene for a key enzyme in the biosynthesis of the phytochrome chromophore. koy-1 seeds are unresponsive to red- and far-red light and hyposensitive under white light. Comparison of hormone and gene expression between wild type and koy- 1 revealed that very low light fluence stimulates germination, while high irradiance of red and far-red light is inhibitory, indicating a dual role of phytochromes in light-regulated seed germination. The mutation also affects the ratio between the two fruit morphs of A. arabicum, suggesting that light reception via phytochromes can fine-tune several parameters of propagation in adaptation to conditions in the habitat. One sentence summaryCharacterization of a phytochrome chromophore biosynthesis mutant demonstrates an active role of phytochromes in the light-inhibited seed germination in Aethionema arabicum.

plant biology↗