Possible role of ARF and AP2 transcription factors in marine and terrestrial evolutionary adaptation of Rhizophoraceae plants unveiled by transcriptomic analysis

Rhizophoraceae has two terrestrial genera and four marine genera. Marine and terrestrial genera have evolved distinct adaptive characteristics to adapt to their environment, among which viviparous reproduction is the most unique. To investigate the genetic foundations difference underlying the adaptive mechanisms of marine–terrestrial genera, we compared the transcriptome of eight tissues (root, stem, leaf, flower, ovule, fruit, seed and embryo) of Kandelia obovata and Carallia brachiata, and found that the mature reproductive organs (fruit, seed and embryo) of K. obovata did not reduce metabolic activity compared to C. brachiata. The reproductive organs of K. obovata were regulated by the same gene set as vegetative organs. This contrasted with C. brachiata. Eight kinds of hormone transduction genes were up-regulated in the seed of K. obovata. Finally, and most importantly, the transcriptional factors AP2 and ARF families were significantly higher expressed in the reproductive organs of K. obovata than those of C. brachiata. At the same time, the ERF family was more expressed in its roots. The findings suggested that hormone transduction may contribute to viviparous initiation. Transcriptional factors were quite crucial for mangrove adaptation to wetlands.