Format: ORAL

Shaohua Xu1, Shao Shao2, Suhua Shi2, Ziwen He2

1 School of Ecology, Sun Yat-sen University, Shenzhen, China 2 School of Life Sciences, Sun Yat-sen University, Guangzhou, China

Although gene loss is common in evolution, it remains unclear whether it is an adaptive process. In a survey of six major mangrove clades that are woody plants in the intertidal zones of daily environmental perturbations, we noticed that they generally evolved reduced gene numbers. We then focused on the largest clade of Rhizophoreae and observed the continual gene set reduction in each of the eight species. A great majority of gene losses are concentrated on environmental interaction processes, presumably to cope with the constant fluctuations in the tidal environments. Genes of the general processes for woody plants are largely retained. In particular, fewer gene losses are found in physiological traits such as viviparous seeds, high salinity and high tannin content. Given the broad and continual genome reductions, we propose the May-Wigner theory (MWT) of system stability as the underlying mechanism. In MWT, the most effective solution for buffering continual perturbations is to reduce the size of the system (or to weaken the total genic interactions). Extending MWT to gene regulatory networks (GRNs), computer simulations and transcriptome analyses support the stabilizing effects of smaller gene sets in mangroves vis-a-vis inland plants. In summary, we show the adaptive significance of gene losses in mangrove plants, including the specific role of promoting phenotype innovation and a general role in stabilizing GRNs in unstable environments as predicted by MWT.