Cis-Effects Condition the Induction of a Major Unfolded Protein Response Factor, ZmbZIP60, in Response to Heat Stress in Maize

Abstract

Adverse environmental conditions such as heat and salt stress create endoplasmic reticulum (ER) stress in maize and set off the unfolded protein response (UPR). A key feature of the UPR is the upregulation of ZmbZIP60 and the splicing of its messenger RNA. We conducted an association analysis of a recombinant inbred line (RIL) derived from a cross of a tropical founder line, CML52 with a standard temperate line, B73. We found a major QTL conditioning heat-induced ZmbZIP60 expression located cis to the gene. Based on the premise that the QTL might be associated with the ZmbZIP60 promoter, we evaluated various maize inbred lines for their ability to upregulate the expression of ZmbZIP60 in response to heat stress. In general, tropical lines with promoter regions similar to CML52 were more robust in upregulating ZmbZIP60 in response to heat stress. This finding was confirmed by comparing the strength of the B73 and CML52 ZmbZIP60 promoters in transient maize protoplast assays. We concluded that the upstream region of ZmbZIP60 is important in conditioning the response to heat stress and was under selection in maize when adapted to different environments.Summary: Heat stress has large negative effects on maize grain yield. Heat stress creates ER stress in maize and sets off the UPR. We searched for factors conditioning heat induction of the UPR in maize seedlings by conducting an association analysis based on the upregulation of unspliced and spliced forms of ZmbZIP60 mRNA (ZmbZIP60u and ZmbZIP60s, respectively). ZmbZIP60u was upregulated more robustly by heat stress in the tropical maize line, CML52, than in B73, and a major QTL derived from the analysis of RILs from a cross of these two lines mapped in the vicinity of ZmbZIP60. We conducted a cis/trans test to determine whether the QTL was acting as a cis regulatory element or in trans, as might be expected for a transcription factor. We found that the QTL was acting in cis, likely involving the ZmbZIP60 promoter. ZmbZIP60 promoters in other temperate and tropical lines similar to CML52 showed enhanced expression of ZmbZIP60u by heat. The contribution of the CML52 promoter to heat induction of ZmbZIP60 was confirmed by analyzing the CML52 and B73 promoters linked to a luciferase reporter and assayed in heat-treated maize protoplasts.

A 1232 bp upstream sequence of glutamine synthetase 1b from Eichhornia crassipes is a root-preferential promoter sequence

“…a The tobacco root transformed with plasmid pBI121; b The tobacco root transformed with plasmid p1200::GUS; c The tobacco root transformed with plasmid p900::GUS; d The tobacco root transformed with plasmid p600::GUS; e The tobacco root transformed with plasmid p400::GUS; f The tobacco root transformed with plasmid pBI101; g The wild tobacco root showed that the upstream of the promoter sequence contained many core elements such as TATA-box (− 30 bp) and CAAT-box (− 96 bp), and the distance from TATA-box or CAAT-box to TSS was consistent with that of the results described in the previous studies in other plant promoters [29]. Besides the core components TATA-box and CAAT-box, the EcGS1b-P also had rootspecific function motif and cis-acting elements that were regulated by light, heat, hormones and temperature, which was also consistent with the previous studies [54][55][56][57]. It is worth to note that GS1b promoter contained root-specific expression element ROOT-MOTIFTAPOX, which indicated EcGS1b might be a root-preferential expression gene.…”

Heat Stress Responses and Thermotolerance in Maize

“…Heat induces the splicing of bZIP60 by IRE1 (inositol-requiring enzyme 1); IRE1 confers heat stress tolerance, and this is attributable to its RNase domain [51,52] bZIP60, HSFTF13, HSPs Maize Maize heat stress response; bZIP60 links the UPR (unfolded protein response) to the HSR in maize by direct binding bZIP60 to the promoter of Hsftf13 to active its expression [14] bZIP60 Maize bZIP60 expression levels in tropical and temperate maize lines with different heat tolerances [53] Others transcriptional processes ABA/ calcium/ SA/ethylene, etc.…”

IRE1-bZIP60 Pathway Is Required for Nicotiana attenuata Resistance to Fungal Pathogen Alternaria alternata

“…Heat, salt, drought, extreme osmotic and heavy metals stresses can activate the UPR in plant cell ( Gao et al., 2008 ; Deng et al., 2011 ; Liu et al., 2011 ; Wang et al., 2011 ; Zhang et al., 2017 ; Li et al., 2018 ). There are also some reports linking pathogen attack and the activation of UPR ( Tateda et al., 2008 ; Moreno et al., 2012 ; Ye et al., 2012 ; Sun et al., 2013 ).…”