Abstract
SummaryHeat stress induces misfolded protein accumulation in endoplasmic reticulum (ER), which initiates the unfolded protein response (UPR) in plants. Previous work has demonstrated the important role of a rice ER membrane‐associated transcription factor OsbZIP74 (also known as OsbZIP50) in UPR. However, how OsbZIP74 and other membrane‐associated transcription factors are involved in heat stress tolerance in rice is not reported. In the current study, we discovered that OsNTL3 is required for heat stress tolerance in rice. OsNTL3 is constitutively expressed and up‐regulated by heat and ER stresses. OsNTL3 encodes a NAC transcription factor with a predicted C‐terminal transmembrane domain. GFP‐OsNTL3 relocates from plasma membrane to nucleus in response to heat stress and ER stress inducers. Loss‐of‐function mutation of OsNTL3 confers heat sensitivity while inducible expression of the truncated form of OsNTL3 without the transmembrane domain increases heat tolerance in rice seedlings. RNA‐Seq analysis revealed that OsNTL3 regulates the expression of genes involved in ER protein folding and other processes. Interestingly, OsNTL3 directly binds to OsbZIP74 promoter and regulates its expression in response to heat stress. In turn, up‐regulation of OsNTL3 by heat stress is dependent on OsbZIP74. Thus, our work reveals the important role of OsNTL3 in thermotolerance, and a regulatory circuit mediated by OsbZIP74 and OsNTL3 in communications among ER, plasma membrane and nucleus under heat stress conditions.
Highlights
Global climate change, including an increase in average temperatures and atmospheric CO2 concentrations, has great impacts on plant growth and yield production (Lesk et al, 2016; Lobell et al, 2011)
To examine the effects of abiotic stresses on OsNTL3 expression, wild-type rice seedlings were subjected to various stress treatments, including endoplasmic reticulum (ER) stress inducers tunicamycin (TM) and dithiothreitol (DTT), salt stress (NaCl), osmotic stress (PEG), phytohormone (ABA) and temperature stresses (4 °C and 45 °C), and the expression of OsNTL3 was analysed by quantitative RT–PCR
It was found that myc-OsNTL3ΔC is enriched significantly at the promoter regions of OsbZIP74 and other OsNTL3-dependent genes (Figure 4d). These results demonstrated that OsNTL3 directly binds to OsbZIP74 promoter and regulates the expression of OsbZIP74 in rice under heat stress conditions
Summary
Global climate change, including an increase in average temperatures and atmospheric CO2 concentrations, has great impacts on plant growth and yield production (Lesk et al, 2016; Lobell et al, 2011). Plants have evolved to cope with the fluctuating environmental temperature conditions with complex and interconnected signalling pathways essential for growth and development (Bita and Gerats, 2013; Bokszczanin et al, 2013). The major injuries in plants are the loss of membrane integrity/fluidity and protein stability (Bita and Gerats, 2013). During HSR in plants, disruption of the interaction between heat shock proteins (HSPs) and heat shock transcription factors (HSFs) at high temperature leads to sequential activation of HSFs and up-regulation of downstream genes encoding HSPs and other factors for enhancing protein folding capacity (Nover et al, 2001; Ohama et al, 2016)
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