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Abstract
In the dry and hot Mediterranean regions wheat is greatly susceptible to several abiotic stresses such as extreme temperatures, drought, and salinity, causing plant growth to decrease together with severe yield and quality losses. Thus, the identification of gene sequences involved in plant adaptation to such stresses is crucial for the optimization of molecular tools aimed at genetic selection and development of stress-tolerant varieties. Abscisic acid, stress, ripening-induced (ASR) genes act in the protection mechanism against high salinity and water deficit in several plant species. In a previous study, we isolated for the first time the TtASR1 gene from the 4A chromosome of durum wheat in a salt-tolerant Tunisian landrace and assessed its involvement in plant response to some developmental and environmental signals in several organs. In this work, we focused attention on ASR genes located on the homoeologous chromosome group 4 and used for the first time a Real-Time approach to “in planta” to evaluate the role of such genes in modulating wheat adaptation to salinity and drought. Gene expression modulation was evaluated under the influence of different variables – kind of stress, ploidy level, susceptibility, plant tissue, time post-stress application, gene chromosome location. ASR response to abiotic stresses was found only slightly affected by ploidy level or chromosomal location, as durum and common wheat exhibited a similar gene expression profile in response to salt increase and water deficiency. On the contrary, gene activity was more influenced by other variables such as plant tissue (expression levels were higher in roots than in leaves), kind of stress [NaCl was more affecting than polyethylene glycol (PEG)], and genotype (transcripts accumulated differentially in susceptible or tolerant genotypes). Based on such experimental evidence, we confirmed Abscisic acid, stress, ripening-induced genes involvement in plant response to high salinity and drought and suggested the quantification of gene expression variation after long salt exposure (72 h) as a reliable parameter to discriminate between salt-tolerant and salt-susceptible genotypes in both Triticum aestivum and Triticum durum.
Highlights
In the Mediterranean regions characterized by hot and dry climates, wheat is subjected to several abiotic stresses such as heat, drought, and salinity
Alignments of Mahmoudi TtASR1 gene with Svevo ASR sequences on chromosomes 4A and 4B are depicted in Supplementary Figures 1a, 2a: sequence of Mahmoudi almost perfectly matched with TtASR-4A of Svevo: the two genes showed a similarity percentage of 99%, encountering only one SNP in the first exon and three SNPs in the second exon, with the last two not influencing protein sequence nor function as falling into the stop codon
The present alignment confirmed gene prediction reported by Hamdi et al (2020): Mahmoudi ASR gene accounts for two exons (225 and 186 bp) separated by one short intron (96 bp) having the same features of Svevo; the only difference relies upon the stop codon (TGA in Mahmoudi, TAG in Svevo)
Summary
In the Mediterranean regions characterized by hot and dry climates, wheat is subjected to several abiotic stresses such as heat, drought, and salinity. The exact physiological function and mechanism of action of ASR genes remain unclear, they are a key component in several plant regulatory networks (Philippe et al, 2010; Gonzàlez and Iusem, 2014). This gene family is gaining a lot of importance during the last years as shown to be associated with the modulation of plant adaptation to high salinity and water loss occurring in both physiological and stressed conditions (Leng et al, 2013). The involvement of ASR genes in plant drought and salt tolerance was documented in several species such as Pinus taeda (Padmanabhan et al, 1997), Lilium longiflorum (Huang et al, 2000), Vitis vinifera (Cakir et al, 2003), Solanum lycopersicum L. (Kalifa et al, 2004), Brachypodium distachyon (Wang et al, 2016), Oryza sativa L. (Li et al, 2017), Zea mays L. (Liang et al, 2019)
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