Transcriptome Analysis Of Different Photosynthetic Types Of Flaveria Under Low CO₂

A massive decline in atmospheric CO₂ levels was the main driver of C₄ evolution before55-40 million years.And C₄ photosynthesis appeared after pro-Kranz,C₂ photosynthesis,up-regulated genes and majorization.According to the different ways of plant carbon assimilation,photosynthesis pathways were divided into C₃,CAM and C₄ pathways.Compared with the C₃ pathway,the C₄ pathway has the advantages of more efficient light energy conversion efficiency,moisture,and nitrogen utilization.Food crops such as wheat and rice are all C₃ crops.Because the C₄ pathway is significantly superior to the C₃ pathway,the transformation of photosynthetic pathways has been under investigation to increase the output of food crops.Our study selected Flaveria as typical material of C₄ evolution.There are so many C₃-C₄species beside C₃ and C₄ species in Flaveria.We selected Flaveria robusta as C₃ plants,Flaveria ramosissima as C₃-C₄ plants and Flaveria bidentis as C₄ plants.The effects of low CO₂concentration on the growth of these plants were explored through control experiments at 380ppm and 100 ppm CO₂ concentrations for different photosynthetic plant materials,and we analyzed the differences in gene expression of different Flaveria and the differences in response to low CO₂ concentrations,providing new clues for transforming photosynthetic pathways at the transcriptome level.1?The effects of low CO₂ on different Flaveria plants.Firstly,it was found that Flaveria robusta?C₃?obviously changed below low CO₂,such as the decrease of plant height,fresh weight of the eighth leaves,chlorophyll content,and stomatal density.And?¹³C was higher.Secondly,it was found that Flaveria ramosissima?C₃-C₄?obviously changed below low CO₂,such as the decrease of plant height,fresh weight of the eighth leaves,chlorophyll content,stomatal density and?¹³C.Flaveria ramosissima?C₃-C₄?delayed flowering.There were a few changes on Flaveria bidentis?C₄?under 100 ppm CO₂.Plant height,main stem leaf numbers and leaf cross section weren't changed visibly.Fresh weight of the eighth leave and chlorophyll content were a little fall.?¹³C,stomatal density and stomatal area were elevated.2?The effects of low CO₂ concentration on cross section of different Flaveria.It was found that there was no Kranz structure in Flaveria robusta?C₃?,and that Flaveria bidentis?C₄?had a distinct Kranz structure.Flaveria robusta?C₃?leaves were thinner,the mesophyll cells were more loose and the palisade tissue was more loosely arranged under low CO₂;Flaveria ramosissima?C₃-C₄?was not obvious in leaf thickness,Flaveria bidentis real leaf cross section difference is not obvious.Flaveria ramosissima?C₃-C₄?had no significant difference in leaf thickness,but loosely arranged cells;There was not obvious at real leaf cross section of Flaveria bidentis?C₄?.3?Expression differences of different Flaveria genes related to C₄ cycle and C₄ related transporters under normal CO₂ concentration.The transcripts associated with C₄ cycle,such as PPDK,ppcA and NADP-ME,were significantly higher in Flaveria bidentis?C₄?and Flaveria ramosissima?C₃-C₄?than in Flaveria robusta?C₃?.4?Different gene expression differences of Flaveria under low CO₂ concentration.Compared with Flaveria robusta?C₃?under normal CO₂ concentration,the number of unigene differentially expressed by Flaveria robusta?C₃?was 1443,and 957 genes were up-regulated and486 genes were down-regulated under low CO₂ concentration.We found that 24 genes involved in the C₄ cycle and transporters,6 genes involved in photorespiration,12 genes involved in carbon metabolism,and 8 genes related to nitrogen metabolism.Compared with Flaveria ramosissima?C₃-C₄?under normal CO₂ concentration,the number of unigene differentially expressed by Flaveria ramosissima?C₃-C₄?was 408,and 179 genes were up-regulated and 229genes were down-regulated under low CO₂ concentration.The genes involved in photorespiration,carbon metabolism,nitrogen metabolism were down-regulated.We found 24genes related to the C₄ cycle and transporters.Compared with Flaveria bidentis?C₄?under normal CO₂ concentration,the number of unigene differentially expressed by Flaveria bidentis?C₄?was 1199,and 640 genes were up-regulated and 559 genes were down-regulated under low CO₂ concentration.We found 23 genes associated with the C₄ cycle and transporters,2photorespiration,and 8 carbon metabolism genes.This experiment laid the foundation for further transformation of the photosynthetic pathway.The differences in responses of different photosynthetic types of Flaveria to low CO₂ concentrantion may provide new clues for transforming the photosynthetic pathway.