A blueprint of seed desiccation sensitivity in the genome of Castanospermum australe

Most angiosperms produce seeds that are desiccated on dispersal with the ability to 30 retain viability in storage facilities for prolonged periods. However, some species produce 31 desiccation sensitive seeds which rapidly lose viability in storage, precluding ex situ 32 conservation. Current consensus is that desiccation sensitive seeds either lack or do not 33 express mechanisms necessary for the acquisition of desiccation tolerance. 34 We sequenced the genome of Castanospermum australe, a legume species producing 35 desiccation sensitive seeds, and characterized its seed developmental physiology and -36 transcriptomes. 37 C. australe has a low rate of evolution, likely due to its perennial life-cycle and long 38 generation times. The genome is syntenic with itself, with several orthologs of genes from 39 desiccation tolerant legume seeds, from gamma whole-genome duplication events being 40 retained. Changes in gene expression during development of C. australe seeds, as 41 compared to desiccation tolerant Medicago truncatula seeds, suggest they remain 42 metabolically active, prepared for immediate germination. 43 Our data indicates that the phenotype of C. australe seeds arose through few changes 44 in specific signalling pathways, precluding or bypassing activation of mechanisms 45 necessary for acquisition of desiccation tolerance. Such changes have been perpetuated as 46 the habitat in which dispersal occurs is favourable for prompt germination