Comparative transcriptomic analysis of heterophylly of the aquatic plant Potamogeton octandrus (Potamogetonaceae)

Abstract

Many plant species exhibit heterophylly, displaying different leaves upon a single plant.The molecular mechanisms regulating this phenomenon, however, have remained elusive.In this study, the transcriptomes of submerged and floating leaves of an aquatic heterophyllous plant, Potamogeton octandrus Poir, were sequenced using a highthroughput sequencing technique (RNA-Seq), which aims to assist with the gene discovery and functional studies of genes involved in heterophyllous leaf development. 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 total of 24,025 differentially expressed genes 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. This study describes the initial results of the high-throughput transcriptome sequencing of heterophylly. Understanding the transcriptomes of floating and submerged leaves of the aquatic plant P. octandrus will assist with gene cloning and functional studies of genes involved in leaf development. This is especially the case with those involved in heterophyllous leaf development. 36 Understanding the transcriptomes of floating and submerged leaves of the aquatic plant P.37 octandrus will assist with gene cloning and functional studies of genes involved in leaf 38 development. This is especially the case with those involved in heterophyllous leaf development. (Minorsky, 2003; Zotz, Wilhelm & Becker, 45 2011). In some cases, heterophylly is believed to be an adaptive response to the environment, 46 and it has been linked to an increase in fitness (Cook & Johnson, 1968; Wells & Pigliucci, 2000; 47 Minorsky, 2003). For example, the heterophylly of aquatic plants may increase their fitness by 48 decreasing leaf damage, decreasing water loss, enhancing photosynthesis, or promoting sexual 49 reproductive success (Winn, 1999a,b; Wells & Pigliucci, 2000; Minorsky, 2003; Zhang et al., 50 2009;Zotz, Wilhelm & Becker, 2011). Accordingly, heterophylly has been used as a model 51 system for studying gene-environment interactions (Pigliucci, 2010; Nakayama et al., 2014). 52In the past century, numerous studies have been conducted to describe morphological 53 changes in heterophyllous plants in response to environmental factors such as CO 2 concentration, 54 oxygen capacity, salt concentration, temperature, water level, seasonal change, and light intensity 55 and quality (McCallum, 1902;Arber, 1920; Fassett, 1930; Sculthorpe, 1967; Cook & Johnson, 56 1968;Bodkin, Spence & Weeks, 1980; Deschamp & Cooke, 1984; Titus & Sullivan, 2001 88 on a single plant is controlled through multiple signalling pathways (Lin & Yang, 1999; Hsu et 89 al., 2001). Thus, wh...