Abstract
SummaryTranscription factors play a key role to enable plants to cope with abiotic stresses. DREB2 regulates the expression of several stress‐inducible genes and constitutes major hubs in the water stress signalling webs. We cloned and characterized a novel gene encoding the FpDREB2A transcription factor from Fraxinus pennsylvanica, and a yeast activity assay confirmed its DRE binding and transcription activation. Overexpression of FpDREB2A in R. pseudoacacia showed enhanced resistance to drought stress. The transgenic plant survival rate was significantly higher than that of WT in soil drying and re‐watering treatments. Transgenic lines showed a dramatic change in root architecture, and horizontal and vertical roots were found in transgenic plants compared to WT. The vertical roots penetrated in the field soil to more than 60 cm deep, while horizontal roots expanded within the top 20–30 cm of the soil. A physiological test demonstrated that chlorophyll contents were more gradually reduced and that soluble sugars and proline levels elevated more sharply but malondialdehyde level stayed the same (P < 0.05). Plant hormone levels of abscisic acid and IAA were higher than that of WT, while gibberellins and zeatin riboside were found to be lower. The root transcriptomes were sequenced and annotated into 2011 differential expression genes (DEGs). The DEGs were categorized in 149 pathways and were found to be involved in plant hormone signalling, transcription factors, stimulus responses, phenylalanine, carbohydrate and other metabolic pathways. The modified pathways in plant hormone signalling are thought to be the main cause of greater horizontal and vertical root development, in particular.
Highlights
Black locust (Robinia pseudoacacia L.), a native tree of North America (Zhang et al, 2007), characterized as a nitrogen-fixing leguminous forest tree species with fast growth, rapid propagation, hard texture and the ability to adapt to different sites and climates (Li et al, 2013a)
This study describes the transformation of FpDREB2A to R. pseudoacacia ‘Idaho’ with comprehensive physiological and transcriptome analysis for enhancing drought stress through improved roots
DRE-binding and transcriptional activation activities of the DREBs The two yeast strains with cis-acting elements DRE (TACCGACAT) and mDRE (TATTTTCAT) were transformed with pAD, pADFpDREB2A, pAD-MtDREB1A and pAD-MtDREB1C plasmids, inoculated on selective YPAD culture medium (Figure 1a)
Summary
Black locust (Robinia pseudoacacia L.), a native tree of North America (Zhang et al, 2007), characterized as a nitrogen-fixing leguminous forest tree species with fast growth, rapid propagation, hard texture and the ability to adapt to different sites and climates (Li et al, 2013a). Due to the tree morphology such as thin pinnate leaves, water loss by transpiration is high in severe drought stress condition (Yang et al, 2006). Keeping this water-deficit condition in mind, the rooting mechanism is an important factor to be studied. The simple supposition is that more profuse root systems could absorb more moisture from surrounding soil, while vertical-extensive roots absorb water more efficiently from moist soil found at deeper levels, in particular (Grieder et al, 2014) Various factors such as genetic (Kell, 2011) and hormonal control (Santner et al, 2009) influence root growth and root system expansion. It is crucial to improve drought resistance in R. pseudoacacia for reclaiming up arid lands by utilizing genetic engineering techniques
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