The contribution of SERF1 to root-to-shoot signaling during salinity stress in rice

Abstract

Stress perception and communication play important roles in the adaptation of plants to changing environmental conditions. Plant roots are the first organs to detect changes in the soil water potential induced by salt stress. In the presence of salinity stress, root-to-shoot communication occurs to adjust the growth of the whole plant. So far, the phytohormone abscisic acid (ABA), hydraulic signals and reactive oxygen species (ROS) have been proposed to mediate this communication under salt stress. Recently, we identified the rice transcription factor SALT-RESPONSIVE ERF1 (SERF1), which regulates a ROS-dependent transcriptional cascade in roots required for salinity tolerance. Upon salt stress, SERF1 knockout mutant plants show an increased leaf temperature as compared with wild type. As this occurs within the first 20 min of salt stress, we here evaluated the involvement of SERF1 in the perception of salt stress in the shoot. By metabolic profiling and expression analysis we show that the action of SERF1 in signal communication to the shoot is independent from ABA, but does affect the accumulation of ROS-related metabolites and transcripts under short-term salt stress.

Keywords: Oryza sativa; metabolism; reactive oxygen species; root-to-shoot; salt stress; transcription factor.

Figure 1. Loss of SERF1 alters the transcriptional response of signaling components in leaves. Expression levels of (A) MAPK signaling genes and (B) calcium signaling-related genes were measured in leaves of wild-type and serf1 plants subjected to salt stress for 30 min or 3 h (100 mM NaCl). ACTIN (Os03g50885) was used as reference gene. Data represent means ± SE from 3 biological replicates. An asterisk (*) indicates a significant difference between treated and control plants (P ≤ 0.05; the Student t test). In the heat map the gene expression under H₂O₂ (5 mM), ABA (5 µM) or mannitol (100 mM) treatment is shown in log₂FC relative to the control situation with n = 3. Os06g43030 and Os07g43900 encode protein kinases. WT; wild type; FC, fold change.

Figure 2. SERF1 influences the transcriptional response of genes relevant for ionic and osmotic homeostasis in leaves. Expression levels of genes encoding (A) ion channels, (B) transporters, (C) aquaporins and (D) ATPases were measured in leaves of wild-type and serf1 plants subjected to salt stress for 30 min or 3 h (100 mM NaCl). ACTIN (Os03g50885) was used as reference gene. Data represent means ± SE from 3 biological replicates. An asterisk (*) indicates a significant difference between treated and control plants (P ≤ 0.05; the Student t test). In the heat map the gene expression under H₂O₂ (5 mM), ABA (5 µM) or mannitol (100 mM) treatment is shown in log₂FC relative to the control situation with n = 3. The potassium channels SKOR* and SKOR** are encoded by Os04g36740 and Os06g14030, respectively. Os06g46670, Os07g01310, Os09g26160 and Os09g31160 encode GLRs. CaCA* and CaCA** are encoded by Os11g01580 and Os12g42910, respectively. Os07g26640 encodes an aquaporin. FC, fold change; WT, wild type; GLR, glutamate-like receptor; CaCA, calcium cation antiporter.

Figure 3. Effect of SERF1 on the expressional response of transcription factor genes in leaves. Expression levels of transcription factor genes and salt stress markers were measured in leaves of wild-type and serf1 plants subjected to salt stress for 30 min or 3 h (100 mM NaCl). ACTIN (Os03g50885) was used as reference gene. Data represent means ± SE from 3 biological replicates. An asterisk (*) indicates a significant difference between treated and control plants (P ≤ 0.05; the Student t test). In the heat map the gene expression under H₂O₂ (5 mM), ABA (5 µM) or mannitol (100 mM) treatment is shown in log₂FC relative to the control situation with n = 3. WT; wild type; FC, fold change.