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Institut für Pflanzenernährung

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Browsing Institut für Pflanzenernährung by Person "Hernandez Pridybailo, Andres"

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    Physiological, molecular, and epigenetic aspects of early transient nitrogen deprivation recovery in maize
    (2024) Hernandez Pridybailo, Andres; Ludewig, Uwe
    Maize is a widely cultivated crop and a primary food source for humans and livestock. Along with its substantial contribution to biomass for fuel production, maize is the most produced cereal globally. However, despite its prevalence, improving nitrogen (N) use efficiency in maize presents ongoing challenges. Understanding how maize plants utilize nitrogen is crucial for identifying traits that could aid breeders in addressing this efficiency gap. When plants experience transient stress and return to previous conditions, a recovery phase is initiated, acclimating the plants and potentially enhancing their responses to subsequent stress events. This mild or transient stress is termed "eustress," and its intentional manipulation is referred to as "crop priming." Crop priming, extensively studied in the context of drought, was explored in our previous research, which revealed that nitrogen supplementation during recovery from early transient water deficits enhances priming effects. This highlights the pivotal role of N in priming and that impaired N supply might negatively affect any acclimation to future stresses. Notably, there is limited literature on transient N deprivation, with most studies focusing on plant responses under conditions of maintained N deficiency. Furthermore, epigenetic regulation of plant mineral nutritional responses via DNA methylation has been reported, like many aspects of plant development that are regulated by such mechanism. Epigenetics is the study of phenotypic changes that can be inherited through mitosis or meiosis, which cannot be explained by changes in the DNA sequence. DNA methylation is the covalent modification of cytosines by the addition of a methyl group, which, depending on its location in the genome, can affect genomic stability and gene expression. Previous results have revealed that N deficiency modifies the methylome of maize roots, hypomethylating transposable elements in a nutrient-specific way. Weak correlations between DNA methylation and gene expression were observed, but a deeper insight into how this covalent modification of cytosines is related to plant mineral nutrition is lacking. DNA methylation patterns are heritable in a sort of “epigenetic memory” and may arise after an environmental stimulus. Here, the role of DNA methylation and its relationship with physiological responses during transient N deprivation were studied. The Fast-Flowering Mini-Maize inbred line A (FFMM-A) was chosen for this study because it can be easily grown hydroponically under controlled conditions. Maize ear leaves recovering from initial nitrogen deprivation (without water limitation) exhibited tissue-specific differences in rapidly dividing meristematic and mature photosynthetically active tissues. Through a series of experiments, a 60 h N deprivation period at the V1 stage was established as a nutritional stress that allowed plants to show mild N deprivation symptoms from which the plants fully recovered. Kinematic analysis of the recovering ear leaf revealed a slight decrease in leaf blade length due to reduced leaf meristem size and leaf number, resulting in a reduced cell production rate. Interestingly, the leaf elongation rate (LER) was maintained, causing a higher specific leaf area, which affected the leaf blade structure. Transcriptomic analysis of the cell division and maturation zones of the recovering ear leaf showed altered gene expression related to cell cycle, lipid metabolism, and secondary metabolism, including phytohormone regulation. Notably, cell cycle-related proteins are also involved in DNA repair and may be involved in somatic memory effects. If plants that had been exposed to early transient N-deficiency stress were later subjected to a second N-deprivation stress at the V5 stage, physiological measurements showed that early N deprivation affected upper leaf chlorophyll accumulation during late N-deprivation recovery. These findings suggest that early N deprivation has long-term effects, especially in dividing tissues, from which young and mature tissues are produced by replication. Furthermore, I identified that the loss of DNA methylation makes maize plants more susceptible to early N deprivation. Loss-of-function zmet2 allele was used in this study. Examination of the methylome of the zmet2 and zmet5 mutants provided insights into the relationship between DNA methylation patterns, nitrogen responses, and the expression of developmentally regulated genes in the leaf. These alleles correspond to CHROMOMETHYLASE3-like maintenance methyltransferase genes, and their mutation causes generalized genome hypomethylation, mostly in the CHG and CHH contexts. After a 96 h N deprivation period at the V1 stage, the zmet2 mutants failed to modify their root-to-shoot ratio and to maintain the LER, with respect to the isogenic B73 line. Moreover, machine learning identified interesting clusters according to their expression patterns from the leaf transcriptome of the dividing and maturation zones of FFMM-A plants. Reanalysis of publicly available datasets from B73 seedling leaf methylation patterns and those of the zmet2 and zmet5 mutants was used to compare the expression patterns of the gene clusters, their methylation patterns, and selected genome features. Interestingly, the methylation pattern of the gene body was highly correlated with the level of expression in the dividing zone of the developing ear leaf. Collectively, mutants in the methylation maintenance pathway, rather than being susceptible to N deprivation, failed to develop symptoms of recovery from such stress, which might be related to the regulation of N metabolism-related genes by DNA methylation. Additionally, the closely related gene expression pattern in the dividing zone and intron non-CpG methylation suggests an intimate role of maintenance of DNA methylation in N nutrition.