Functional Analyses Of Two Genes That Control The Environmental Signaling Responses In Plants

Unlike animals, plants can not "walk away" from the harmful environment. However, they have evolved elaborate mechanisms to deal with the changes of outside environments. That is to say, plants can acquire their adaptation to stress environments by controlling growth and development on the basis of environmental signals. Therefore, it’s one of the hottest research realms in plant molecular ecology to dissect molecular mechanisms between growth and development of plants and their responses to environmental signals.Plants fulfill their responses to environmental signals through a series of intra-and extra-cellular proteins. Among them, the plasma membrane-located receptor-like protein kinases (RLKs) are able to sense extra-cellular signals, and switch on corresponding elaborate responses. Ankyrin repeat proteins (adaptor proteins) mediate protein-protein interactions in cells by recruiting proteins through ankyrin repeat motif "adaptor", thus enable plants to response specifically to the outer environmental changes, and acquire adaptation to environments by means of controlling growth development.We chose the FERONIA (FER) receptor kinase and ANK6ankyrin repeat protein as the starting point, to analyze their functions in plant ecological environmental responses and relations to plant growth development. These will promote us to understand the molecular mechanisms that plants adapt to environments. The main conclusions are as follows:First, functions of receptor like kinase FER in the stress hormones signal transduction1. FER-GEF1/4/10-ROP11-ABI2pathway was identified as positive regulation signal of a core factor of ABA responses, ABI2for the first time.ABA is an important stress hormone. There are reporters that the ABA receptor proteins can inhibit the PP2CA (ABI2) activity. We identified a pathway which is composed of FER-GEF1/4/10-ROP11positively regulating ABI2activity and inhibit the ABA response. Both this pathway and the PP2CA negatively regulate pathway formed the "Ying-Yang" faces of the PP2CA activity regulators. On the other hand, ABI2physically interacts with the FER kinase, suggesting a feedback inhibition of FER by dephosphorylation, and so characterized an ABA response circuit by using FER as a node. This signal circuit will help us better understanding mechanisms of the guard cell open/closure and stress response control.2. FER was identified as negatively regulator of the ethylene substrate synthetase SAM1and SAM2for the first timeEthylene is another stress response hormone. The S-adenosyl-L-methi- onine (SAM) synthetase (SAM1and SAM2) can synthesize SAM, the precursor of ethylene. We found that FER interacts with SAM1/2on the plasma membrane and negatively regulate SAM synthesis, thereby inhibits ethylene synthesis and stimulates plants stress and development response at last.3. A model was proposed that FER functions as a key node of multiple hormone cross-talks for plant to response stress environmental signalings.According to the environmental signals, FER can regulate many signaling pathways by affecting ABA, ethylene or auxin response, thus get plants to response to abiotic stresses (salt, hot, cold and osmotic stress) or biotic stress, and finally adapt to outer environment by controlling plant growth and development.4. Function of two E3ligases in FER network was analyzed preliminarily.We found that two E3ligase which have high homology can interact with FER and function as positive response factors of FER ABA control pathway. These data will help us understanding the FER network.5. Molecular mechanism of FER in seed size control was analyzedFER displayed high expression and polarity in integuments, and can negatively regulate the seed size through GEF1to inhibit the integument cells elongation. Second, functional analysis of ANK6during fertilizationAnkyrin repeat protein is an "adaptor protein"and can mediate the protein-protein interaction and may have function in the environmental responses in the RLKs mediated pathways. We found that ANK6expression is inhibited by ABA and salt stress. We want to explore the function of ANK6during the environmental response. But the lack of homozygous mutant from a T-DNA insertional line indicated that loss-of-function of ANK6results in embryonic lethality which is very similar to the fer fertilization phenotype. ANK6was localized to the mitochondria where it interacts with SIG5, a transcription initiation factor previously found to be essential for fertility. Moreover, ANK6can interact with a small ribosome subunit protein RPS9in mitochondrial. Loss-of-function of RPS9results in male, female gametophytes development, ABA and salt stress response defect. Unfortunately, as the embryonic lethality limitations, we only analyzed the function of ANK6in fertilization but did not analyze its function in environmental responses. More efforts are required in environmental response study in future.