Abstract
BackgroundAdverse environmental conditions produce ER stress and elicit the unfolded protein response (UPR) in plants. Plants are reported to have two "arms" of the ER stress signaling pathway-one arm involving membrane-bound transcription factors and the other involving a membrane-associated RNA splicing factor, IRE1. IRE1 in yeast to mammals recognizes a conserved twin loop structure in the target RNA.ResultsA segment of the mRNA encoding ZmbZIP60 in maize can be folded into a twin loop structure, and in response to ER stress this mRNA is spliced, excising a 20b intron. Splicing converts the predicted protein from a membrane-associated transcription factor to one that is targeted to the nucleus. Splicing of ZmbZIP60 can be elicited in maize seedlings by ER stress agents such as dithiothreitol (DTT) or tunicamycin (TM) or by heat treatment. Younger, rather than older seedlings display a more robust splicing response as do younger parts of leaf, along a developmental gradient in a leaf. The molecular signature of an ER stress response in plants includes the upregulation of Binding Protein (BIP) genes. Maize has numerous BIP-like genes, and ER stress was found to upregulate one of these, ZmBIPb.ConclusionsThe splicing of ZmbZIP60 mRNA is an indicator of ER stress in maize seedlings resulting from adverse environmental conditions such as heat stress. ZmbZIP60 mRNA splicing in maize leads predictively to the formation of active bZIP transcription factor targeted to the nucleus to upregulate stress response genes. Among the genes upregulated by ER stress in maize is one of 22 BIP-like genes, ZmBIPb.
Highlights
Adverse environmental conditions produce ER stress and elicit the unfolded protein response (UPR) in plants
In response to ER stress, AtbZIP60 is spliced by an ER-localized ribonuclease, IRE1 [27]
Maize has two IRE1 orthologs, it is not clear which one is orthologous to AtIRE1a and which to AtIRE1b, since IRE1-like genes in dicots and monocots lie in two separate clades with soybean IRE1 as an outlier (Additional file 2)
Summary
Adverse environmental conditions produce ER stress and elicit the unfolded protein response (UPR) in plants. Plants are reported to have two “arms” of the ER stress signaling pathway-one arm involving membranebound transcription factors and the other involving a membrane-associated RNA splicing factor, IRE1. Considered an environmental stress sensor in plants, UPR is UPR was first described in plants a number of years ago [11,12,13]-recognized by the upregulation of genes characteristic of the response [14]. It has only been in the past few years that the components of the ER stress signaling pathway were identified in plants [8]. The TFs relocate to the nucleus where they upregulate stress response genes [20]
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