H₂S Responses To Light Signal In Foxtail Millet And Mediates Interplant Communication

Since being confirmed as a gas signal molecules,hydrogen sulfide（H₂S）has attracted increasing attention.It not only helps plants resist environmental stress,but also regulates plants growth and development.Light,a indispensable factor for plant growth,regulates many processes throughout the plant’s life cycle.Both H₂S and light take part in multiple identical processes of plant,but there has been no clear report on their contaction.Foxtail millet is an important gramineous crop in Shanxi Province and northern China,which has been planting for more than 2000 years.It has been approbated as a model crop for plant genes function research because of its small genome,complete sequencing and low DNA reproducibility.In this paper,the foxtail millet was used as experimental material to analyze how the light signals regulate H₂S signal production during the transition from skotomorphogenesis to photomorphogenesis of plant.The main experimental results obtained by detecting the length of hypocotyls,H₂S content,the production rate of H₂S,H₂S-production enzyme encoding genes transcription and translation were as follows:（1）Effect of H₂S on hypocotyl growth.Under dark or white light conditions,exogenous H₂S treatment significantly promoted the elongation of hypocotyls,and exogenous hydroxylamine（HA）treatment significantly inhibited hypocotyl elongation.There was no significant change in hypocotyl length after H₂S or HA treatment under red or blue light conditions.（2）Effect of different light quality on H₂S content.After white,red or blue light irradiation,the H₂S content in the hypocotyls first increased and then decreased.The H₂S content reached the peak（an increase of 59%）after 18 min under white light,or rose to the peak（an increase of 23%）after 6 minutes under red light,or peaked at 12 minutes under blue light（an increase of 22%）respectively.（3）Effect of different light quality on H₂S production rate.The H₂S production rate of hypocotyl decreased after exposure to white light or blue light,while increased after red light irradiation（except for 20 min）.（4）Effects of different light qualities on the expression of enzyme-encoding genes.The transcription levels of H₂S producing enzyme-encoding genes LCD1,LCD2 and DES1 in hypocotyls were significantly increased under white light conditions,while LCD1 and LCD2 increased significantly at different times under red light conditions and no significant change in DES1.Blue light did not influence these genes transcription,except for LCD2,which m RNA increased at 10 min.The LCD protein increased under both white and red light conditions.（5）The protein extract from wild-type or light receptor mutants phya,phyb,cry1,cry2 arabidopsis suffering different light irradiation reacted with the extracts of foxtail millet firstly,and then the H₂S production rate of the reactants were determined.The results indicate that PHYB（red light photoreceptor）may directly regulate the protein activity of H₂S producing enzyme,and red or blue light irradiation cause LCD protein phosphorylation.（6）H₂S as a gasotransmitter for plant communication.The H₂S concentrations in air increased when the foxtail millet,Chinese cabbage,tomato or arabidopsis seedlings were treated with 40% PEG 8000.When foxtail millet or arabidopsis Col-0 were treated with PEG 8000,the H₂S content and the expression levels of the H₂S response genes in the neighboring non-stressed plants were increased,and the stoma of these neighboring plant was also induced closure.However,PEG 8000 treated lcd/des1 could not induce a similar phenomenon of the neighboring plants.Based on the above results,the light signal activates the H₂S signal by regulating the H₂S production enzyme genes expression,and PHYB-mediated phosphorylation modification to regulate the activity of the LCD.H₂S serves as a messenger between plant individuals,that is,by releasing H₂S into the surrounding environment,plants under stress can provide early warning information of stress to their neighboring plants,which may be of great significance to the survival of the population.