Format: ORAL

Shao Shao1, Ziwen He1, Suhua Shi1,*, Shaohua Xu1,*

1 Sun Yat-sen University, Guangzhou, China * Corresponding authors

When experiencing unstable environments, a major challenge for plants is the maintaining stability of gene regulatory networks (GRNs). How plants accumulate genetic changes to stabilize GRNs in the long-term adaptation to environmental fluctuations is rarely revealed. In this study, we proposed a possible strategy of continuously turning on stress-responsive genes, which may increase GRNs stability while increasing energy costs. We tested the hypothesis by comparing expression profiles in a typical mangrove plant Rhizophora apiculata and its inland relative Carallia pectinifolia. Mangroves inhabited intertidal zones with highly fluctuated salinity and other stressors. We found that the gene expression profiles of R. apiculata were more stable than that of C. pectinifolia under salinity changes. It is caused by the transitation of stress-induced expression to constitutive expression in 4,000 genes. The genes include the up-regulation by high salinity in inland plant meanwhile constitutively high-expressed in mangroves and the down-regulation in inland plant and always low-expressed in mangroves. The former are enriched in salt stress response, while the latter are concentrated in the metabolic and development processes such as photosynthesis. We reconstructed GRNs based on time-series expression data and identified 42 key transcription factors that may have dominated the gene expression profile transitation. We also identified genetic changes possiblely responsible for the evolution of mangrove GRNs. In summary, mangroves have undergone extensive changes in gene expression profiles compared to their inland relatives. In particular, many salt stress response genes have evolved from stress-type to constitutive expression, which may be caused by changes in the expression patterns of key genes on GRNs. The growth-defense trade-off, investing more energy in denfense at the cost of growth, may be an important strategy for mangroves to adapt to the fluctuating intertidal environments.