Drought Stress Induces Differential DNA Methylation Shift at Symmetric and Asymmetric Cytosine Sites in the Promoter Region of ZmEXPB2 Gene in Maize

Abstract

β-expansin 2 (EXPB2) gene induces drought tolerance in different plant species including maize. Different epigenetic mechanisms like DNA methylation, histone modification and RNA interference affect the gene activities under stress conditions. DNA methylation, an important epigenetic mechanism, could be involved in the regulation of ZmEXPB2 gene under drought stress in maize. Plants of drought sensitive variety „Jalal‟ were grown till 4th leaf stage under well-watered conditions. At 5th leaf stage, plants were divided in two groups i.e., well-watered (100% water holding capacity) or drought stress (0% water holding capacity for 15 days). Plants subjected to drought stress showed clear signs of stress by significant decrease in fresh weight of whole plant, 6th leaf length, stunted secondary root growth and increased primary root length. DNA methylation profile of three regions (denoted as -1.7 k, -1.3 k and -0.8 k) in the promoter of ZmEXPB2 gene, of root DNA, were evaluated. Under well-watered conditions, heterogeneity in DNA methylation profile along the promoter sequence was observed. Regions -1.7 k and -1.3 k were methylated whereas the region -0.8 k was nonmethylated. After the comparison of DNA methylation profile of well-watered and drought stress plants, no change in -1.7 k and -0.8 k regions was observed. However, the -1.3k region had significant decrease in the DNA methylation at symmetric cytosine sites i.e., cytosine-guanine (CG) dinucleotides and cytosine-adenine/cytosine/thymine-guanine (CHG where H = A, C or T) trinucleotide and significant increase at asymmetric cytosine sites (CHH) under the stress condition. In addition, significant increase in the gene expression of ZmEXPB2 under drought was also observed. In conclusion, drought stress conditions induce DNA hypomethylation at CG, and CHG sites and DNA hypermethylation at CHH sites in the middle region of the promoter of ZmEXPB2 gene. This shift can be associated with the up regulation of ZmEXPB2 gene which in turn increased primary root length as a plant stress response mechanism. © 2021 Friends Science Publishers

Recent Advances in Studies of Genomic DNA Methylation and Its Involvement in Regulating Drought Stress Response in Crops

“…The proportion of methylation changes in response to drought mostly ranged from 10 to 20%, but some showed only slight changes, which may be related to tissue specificity [144]. In contrast, the proportions and trends of methylation sites in the three contexts were different, with the trends of symmetric methylation sites such as CG and CHG remaining the same, whereas most of the CHH asymmetric methylation sites were opposite to the symmetric methylation sites, which might be more sensitive to drought environment; this was confirmed in the study of Zea mays L. and Populus tomentosa [125,135], although methylation of CG, CHG symmetry sites were more sensitive to drought stress in other species of plants studied [126,143].…”

“…Plant dry weight and leaf area were significantly reduced, ΦPSII and increased ΦNPQ, higher photosynthetic rate and stomatal conductance [143] Based on our review of previous studies, we found that in general, plants change the extent of DNA methylation in response to drought stress. While two studies in Table 1 showed a genome-wide decrease in DNA methylation levels [122,125], and six studies showed an genome-wide increase in DNA methylation levels [124,128,136,139,140,142], an increase or decrease in methylation levels of the internal part of promoters of drought response genes was specifically determined by the positive or negative regulation of the gene under drought stress [126,127,130,134,135,137,140,143]. The proportion of methylation changes in response to drought mostly ranged from 10 to 20%, but some showed only slight changes, which may be related to tissue specificity [144].…”

“…Plants appear to employ this dynamic epigenetic mechanism to adeptly manage environmental challenges. Importantly, these alterations in methylation predominantly impact genes and pathways crucial to the drought stress response, including water uptake and root architecture [135], osmotic balance [125], and hormone signaling processes [125,129]. Studies have shown that changes in DNA methylation patterns can activate or suppress the expression of specific genes involved in drought response.…”

Yield and component yield of onion (Allium cepa L.) effect of salicylic acid under drought stress in Indonesia

“…Drought is a factor that significantly disrupts physiological processes in plants (inhibits germination, reduces growth, lowers yields, and interferes with key metabolic processes) (Maksimović et al, 2021;Megala et al, 2022). Its influence is more evident during the reproductive stage than other growth stages, and yields are significantly decreased (Atta et al, 2022;Rehman et al, 2021). The severity, duration, type of plant species, and stage of development affect how plants react to drought stress.…”