The Plasticity And Transcriptomic Studies On Potamogeton Octandrus Poir Heterphyllous Leaves

Heterophylly is observed in many vascular plants,which produce different type leaves upon a single plant.Heterophylly may increase the fitness of aquatic plants in the adaptive evolution.The morphology,anatomical structure,physiological and biochemical indexes and spectral characters of heterophyllous aquatic plants are significantly different.Floating leaves exert more advantages than submerged leaves in order to adapt to different ecological enviroment.The research reports about regulatory mechanisms of heterophylly,related genes and contribution to the populations fitness are not comprehensive.In this article,the effects of environmental factors and plant hormone on heterophyllous aquatic plants are reviewed,and a deeper studying the developmental mechanism of heterophyllou aquatic plants is provided.We used Potamogeton octandrus Poir(Potamogetonaceae),a heterophyllous pondweed with two different leaf forms(submerged and floating),as a study system.In general,aerial and floating leaves are round shaped,thicker,cutinized with stomata,whereas submerged leaves are thin and bear few or no stomata.Water depth is an important ecological factor affecting the growth and reproduction of aquatic plants.The effects of water depth gradient(10cm,30cm,50cm,70cm)on the growth and reproduction of Potamogeton octandrus Poir were studied.Results showed that the water depth gradient significantly affected on stem length,number of clonal ramets,biomass accumulation and biomass allocation patterns of P.octandrus(P<0.05)and P.octandrus is heterophyllous.With the increase of water depth,the indexes of pant height,above ground biomass,number of inflorescenceand fruits of P.octandrus represented a increasing trend.P.octandrus represented the most number of ramets without sexual reproduction at 10 cm depth,whereas the most sexual reproduction with less ramets were found at 50 cm depth.That indicted there was a trade-off between clone reproduction and sexual reproduction.We suggested that P.octandrus showed morphological plasticity along water depth gradient and preferred 50 cm.With a certain range of ABA and GA are facilitated the development of plant shoot apical meristems.Generally,changes in endogenous hormone levels may also contribute to the formation of heterophyllous leaves.The endogenous hormones(ZT,GA3,IAA,ABA)content in submerged leaves and floating leaves were ezamined,and the change trends were analyzed by HPLC method.The results show that the content of GA3 in submerged leaves development process was significantly increased,and was higher than the content of GA3 in floating leaves.On the contrary,the content of ABA kept increasing trend during floating leaves development stages,and the content of ABA in submerged leaves increased decreased showed a trend of increased first and then decreased.During submerged leaves and floating leaves growth,the content of ZT was slightly increased,while the content of IAA in plant shoot was the highest,then was rapidly decrease during submerged leaf and floating leaves development.These changes in content of endogenous hormone may have an effect on the formation of heterophyllous leaves.We sequenced the transcriptomes of the submerged and floating leaf materials at different developmental stages using the Illumina RNA-Seq method.Next,we performed de novo assembly of the short sequence reads generated from all submerged and floating leaf materials as the reference transcriptome,and then mapped the short sequence reads generated from each developmental stage of the submerged and floating leaf onto the assembled transcriptome and identified the genes showing different expression between leaf morphologies.A total of 81,103 unigenes were identified from the submerged and floating leaves,and a total of 6,822 differentially expressed genes(DEGs)were identified by comparing the samples from each developmental stage.KEGG pathway enrichment analysis categorized these unigenes into 128 pathways(p-value<10-5).A number of annotated genes(24,025)were involved in the carbon metabolic pathway,biosynthesis of amino acids,ribosomes,and plant-pathogen interaction.KEGG pathway enrichment analysis categorized a total of 70 DEGs into plant hormone signal transduction pathways.469 putative TF genes belonging to 42 families showed significant differential expression between developmental stages,including WRKY,C3H,AP2,MYB and ARF families.In the functional categories,some genes were clustered to the terms"stomatal complex morphogenesis" and "cuticle development" throughout the leaf development process.23 DEGs were mapped to "stomatal complex morphogenesis"and 11 DEGs were mapped to "cuticle development".Our study provides a reference transcriptome for investigating the regulatory mechanisms of each leaf form and a list of candidate genes likely to be involved in heterophylly development.