Regulation of reactive oxygen species generation under drought conditions in Arabidopsis

Abstract

Responses to adverse environmental conditions are regulated by gene regulatory networks, in which transcription factors play a central role in plants. The NAC transcription factors constitute a representative transcription factor family that mediate diverse aspects of biotic and abiotic stress responses in plants. 1 Notably, some NAC transcription factors are integrated into the intracellular membranes and proteolytically activated upon exposure to developmental and external stimuli.2,3 At least 13 membranebound NAC transcription factors, collectively designated 'NAC with transmembrane motif 1 (NTM1)-like (NTL)' members, have been identified in Arabidopsis. 4 Several NTL genes, such as NTL4, NTL6 and NTL8, have been shown to mediate diverse environmental stress responses. 4A truncated NTL4 form (4ΔC) lacking the TM motif possesses transcriptional activation activity, and 35S:4ΔC transgenic plants exhibit distinct phenotypes, such as reduced growth and alteration of leaf morphology. 5 These observations suggest that the 4ΔC form is closely related with a biologically functional NTL4 form. Notably, the NTL4 gene is significantly induced by drought and heat stresses.5 Diverse plant developmental processes, such as germination and leaf senescence, are profoundly affected by environmental stresses. 6,7 We therefore examined the potential role of the NTL4 gene in drought stress responses. Whereas the 35S:4ΔC transgenic plants were susceptible to drought stress, the ntl4 mutants showed enhanced drought resistance, suggesting that NTL4 gene is involved in drought stress responses. 5 reactive oxygen species (roS) are produced when plants are exposed to environmental stresses, such as drought and heat conditions. oxidative stress imposed by roS under drought conditions profoundly affects plant growth and development. however, roS production and scavenging mechanisms under adverse environmental conditions are largely unknown. We have recently reported that a nam/ataF1/2/CuC2 (naC) transcription factor ntL4 is required for generation of roS under drought conditions in arabidopsis. 35S:4ΔC transgenic plants overexpressing a truncated ntL4 form (4ΔC) lacking the C-terminal transmembrane (tm) motif were hypersensitive to drought stress, and roS accumulated to a high level in the transgenic plants. in contrast, NTL4-deficient ntl4 mutants were less sensitive to drought stress and contained reduced levels of roS. Furthermore, the plasma membrane-associated ntL4 transcription factor is proteolytically activated by treatments with drought and abscisic acid (aBa) and nuclear-localized, where it induces expression of naDPh oxidase genes involved in roS biosynthesis. notably, the 35S:4ΔC transgenic plants showed accelerated leaf senescence and cell death under drought conditions. taken together, these observations indicate that ntL4 regulation of roS generation underlies the drought-induced leaf senescence. Keywords: ABA, arabidopsis, drought stress, leaf senescence, NAM/ATAF1/2/CUC2 (NAC), ROS ROS are toxic materials that cause oxid...

The Arabidopsis Transcription Factor NAC016 Promotes Drought Stress Responses by Repressing AREB1 Transcription through a Trifurcate Feed-Forward Regulatory Loop Involving NAP

“…These experiments were repeated three times with similar results. Examination of the other TMD-containing NACs showed that NAC053/NTL4 positively regulates H 2 O 2 -dependent drought stress responses and NAC017 negatively regulates these responses (Lee and Park, 2012;De Clercq et al, 2013 (Olsen et al, 2005). NAC017 also binds to the core sequence of the NAC binding motif, CACG or CAAG (Ng et al, 2013).…”

“…Conditional Nuclear Localization of NAC016 by Cleavage of the C-terminal TMD under Drought Stress or Prolonged Darkness NAC016 contains a C-terminal TMD , and the C-terminal TMD determines the subcellular localization of other NACs (Lee and Park, 2012;De Clercq et al, 2013;Ng et al, 2013). Thus, to examine whether the C-terminal TMD of NAC016 controls its conditional nuclear localization, we prepared transgenic plants expressing the full-length NAC016 (N16) or NAC016 without the TMD (N16△C).…”

“…Indeed, the binding motifs of other NACs, including ORE1, NAP, NTL4, and NAC017, contain the CACG or CGTG sequences (Olsen et al, 2005;Lee and Park, 2012;Ng et al, 2013;Supplemental Table 6). These results indicate that CACG and CGTG constitute the 4-bp core sequence of the NAC binding motif.…”

“…The NAC TFs that contain a C-terminal TMD, NTL6 (NTL for NAC with transmembrane motif 1-like) and NTL4, also function in drought stress signaling. Indeed, NTL6-OX plants and ntl4 null mutants exhibit drought tolerance (Kim et al, 2012;Lee and Park, 2012), indicating that the functions of NTL4 and NTL6 counteract each other in drought stress-responsive signaling. Notably, their C-terminal TMDs conditionally regulate the TF activities of these two NTLs; under water deficit conditions, cleavage of their TMDs allows NTL6 and NTL4 to translocate from the cytoplasm to the nucleus (Kim et al, 2010;Lee and Park, 2012).…”

Programmed Cell Death as a Response to High Light, UV and Drought Stress in Plants

“…Many of them possess stress responsive cis-regulatory elements in their promoter sequences like abscisic acid-responsive elements (ABRE) and drought-responsive elements (DRE) [189][190][191]. The plasma membrane-associated NTL4 (NAC transcription factor) after drought or ABA treatment has been shown to be proteolytically activated and transported to the nucleus where it induces expression of NADPH oxidase involved in ROS generation [192]. Moreover, the dehydration stimulates expression of BAX inhibitor-1 (AtBI-1).…”