Transcriptional Analyses of Natural Leaf Senescence in Maize

Abstract

Leaf senescence is an important biological process that contributes to grain yield in crops. To study the molecular mechanisms underlying natural leaf senescence, we harvested three different developmental ear leaves of maize, mature leaves (ML), early senescent leaves (ESL), and later senescent leaves (LSL), and analyzed transcriptional changes using RNA-sequencing. Three sets of data, ESL vs. ML, LSL vs. ML, and LSL vs. ESL, were compared, respectively. In total, 4,552 genes were identified as differentially expressed. Functional classification placed these genes into 18 categories including protein metabolism, transporters, and signal transduction. At the early stage of leaf senescence, genes involved in aromatic amino acids (AAAs) biosynthetic process and transport, cellular polysaccharide biosynthetic process, and the cell wall macromolecule catabolic process, were up-regulated. Whereas, genes involved in amino acid metabolism, transport, apoptosis, and response to stimulus were up-regulated at the late stage of leaf senescence. Further analyses reveals that the transport-related genes at the early stage of leaf senescence potentially take part in enzyme and amino acid transport and the genes upregulated at the late stage are involved in sugar transport, indicating nutrient recycling mainly takes place at the late stage of leaf senescence. Comparison between the data of natural leaf senescence in this study and previously reported data for Arabidopsis implies that the mechanisms of leaf senescence in maize are basically similar to those in Arabidopsis. A comparison of natural and induced leaf senescence in maize was performed. Athough many basic biological processes involved in senescence occur in both types of leaf senescence, 78.07% of differentially expressed genes in natural leaf senescence were not identifiable in induced leaf senescence, suggesting that differences in gene regulatory network may exist between these two leaf senescence programs. Thus, this study provides important information for understanding the mechanism of leaf senescence in maize.

Identification of Transcription Factors Regulating Senescence in Wheat through Gene Regulatory Network Modelling

“…For example, early down-regulation of chlorophyllrelated genes is observed in both Arabidopsis (Breeze et al, 2011) and wheat, whereas transport processes are up-regulated later during senescence. The temporal order of senescence-related processes is also broadly conserved in maize although only three time points were sampled, making fine-grain comparisons difficult (Zhang et al, 2014). In rice, a longer time course of flag leaf senescence has been studied (Lee et al, 2017), where the authors mainly focused on comparing flag leaf and second leaf senescence; nevertheless broadly similar processes were observed in both senescing rice leaves and the wheat flag leaf.…”

Integrating transcriptomic and metabolomic analysis to understand natural leaf senescence in sunflower

“…At the transcriptional level, the regulation of senescence has been well studied in model species such as A. thaliana (Gepstein et al, 2003;Lim et al, 2003;Lin and Wu, 2004). Furthermore, this process has been partially assessed in other species such as rice (Lee et al, 2001), tobacco (Pageau et al, 2006), pea (Pic et al, 2002), wheat (Uauy et al, 2006), cotton (Kong et al, 2013), maize (Sekhon et al, 2012;Zhang et al, 2014), turnip (Gombert et al, 2006), barley (Hollmann et al, 2014;Jukanti et al, 2008) and sunflower (Cabello et al, 2006;Fernandez et al, 2012a;Moschen et al, 2014). Transcription factors (TFs) are key proteins in the regulation of gene expression and signal transduction networks regulating different biological processes.…”

Transcription Factor ATAF1 in Arabidopsis Promotes Senescence by Direct Regulation of Key Chloroplast Maintenance and Senescence Transcriptional Cascades

“…Senescence is accompanied by transcriptional reprogramming of a large number of genes, including those encoding transcription factors (TFs), as shown by global transcriptome profiling in various plant species, including Arabidopsis (Arabidopsis thaliana; BuchananWollaston et al, 2005;Balazadeh et al, 2008;Breeze et al, 2011), wheat (Triticum aestivum; Gregersen and Holm, 2007;Cantu et al, 2011), aspen (Populus tremula; Andersson et al, 2004), maize (Zea mays; Zhang et al, 2014), and others. Recently, the role of several NAC (for NO APICAL MERISTEM/ARABIDOPSIS ACTIVATION FACTOR1 [ATAF1-2]/CUP-SHAPED COTYLEDON) TFs for senescence has been reported, and both positive and negative regulators were identified.…”