Abstract
Ethylene is well known as a plant hormone, but its role in bacteria is poorly studied. We recently showed that Synechocystis sp. Strain PCC 6803 has a functional receptor for ethylene, ethylene response 1 (Etr1), that is involved in various processes such as phototaxis in response to directional light and biofilm formation. Here, we use RNA sequencing to examine the changes in gene transcripts caused by ethylene under phototaxis conditions. Over 500 gene transcripts across many functional categories, of approximately 3700 protein‐encoding genes, were altered by application of ethylene. In general, ethylene caused both up‐ and downregulation of genes within a functional category. However, the transcript levels of amino acid metabolism genes were mainly upregulated and cell envelope genes were mostly downregulated by ethylene. The changes in cell envelope genes correlate with our prior observation that ethylene affects cell surface properties to alter cell motility. Ethylene caused a twofold or more change in 62 transcripts with the largest category of upregulated genes annotated as transporters and the largest category of downregulated genes annotated as glycosyltransferases which sometimes are involved in changing the composition of sugars on the cell surface. Consistent with changes in cell envelope, glycosyltransferase, and transporter gene transcripts, application of ethylene altered the levels of specific sugar moieties on the surface of cells. Light signaling from Etr1 involves two proteins (Slr1213 and Slr1214) and a small, noncoding RNA, carbon stress‐induced RNA1 (csiR1). Application of ethylene caused a rapid, but transient, decrease in the transcript levels of etr1, slr1213, and slr1214 and a rapid and prolonged decrease in csiR1 transcript. Deletion of Slr1214 caused a large increase in csiR1 transcript levels and ethylene lowered csiR1 transcript. These data combined with prior reports indicate that ethylene functions as a signal to affect a variety of processes altering the physiology of Synechocystis cells.
Highlights
Ethylene is a gas that acts as a plant hormone to affect growth, development, and responses to stress (Abeles, Morgan, & Saltveit, 1992; Mattoo & Suttle, 1991)
Strain PCC 6803 contains a functional ethylene receptor encoded by the slr1212 gene locus, hereafter referred to as Etr1 for ethylene response 1 as originally designated by Ulijasz and others (Ulijasz et al, 2009)
We examined lectin binding to the surface of Synechocystis cells using fluorescein isothiocyanate (FITC)-labeled peanut agglutinin (PNA) that binds to galactose(b1-3)N-acetyl-D-galactosamine, concanavalin A (ConA) that binds to a-D-mannose and a-D-glucose, or Ulex europaeus agglutinin (UEA) that binds to a-L-fucose and N,N’-diacetylchitobiose
Summary
Ethylene is a gas that acts as a plant hormone to affect growth, development, and responses to stress (Abeles, Morgan, & Saltveit, 1992; Mattoo & Suttle, 1991). Strain PCC 6803 (referred to here as Synechocystis) contains a functional ethylene receptor encoded by the slr1212 gene locus, hereafter referred to as Etr for ethylene response 1 as originally designated by Ulijasz and others (Ulijasz et al, 2009) This receptor, called positive phototaxis A (PixA) and UV intensity response Sensor (UirS), contains an ethylene-binding domain at the N terminus, followed by a phytochrome-like domain that responds to photons, and a C-terminal histidine kinase domain (Lacey & Binder, 2016; Narikawa et al, 2011; Song et al, 2011; Ulijasz et al, 2009). This receptor has two distinct inputs regulating Synechocystis physiology, light and ethylene.
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