Physiologic, Genetic and Epigenetic Determinants of Water Deficit Tolerance in Fruit Trees

Abstract

Fruits are increasingly recognized as an important part of a healthy diet. Fruit crops represent a wide range of woody perennial species grown in orchards. Water availability is a primary environmental factor limiting fruit crop growth and productivity. Erratic rainfall patterns and increased temperatures due to climate change are likely to increase the duration of droughts. This review aims to highlight the different mechanisms by which fruit crops respond to water stress deficits. Emphasis is placed on physiological, genetic and epigenetic determinants of stress response in fruit crops. These findings can contribute to a deeper understanding of the underlying effects of drought. We also describe new research opportunities made possible by the increasing availability of population-level genomic data from the field, including genome-wide association studies (GWAS) and high-throughput phenotyping.

Keywords: drought stress; epigenetic modification; fruit crop; gene editing; gene regulation; genome-wide association studies; polyploidy.

Figure 1

Schematic representation of drought main effects in trees. Transpiration stream from the leaves provides the force needed to move water around the plant [14]. At cellular level, in symplastic pathway, aquaporines may regulate the water flux (green box). In this way, water is transferred from the soil to the roots. In stress condition (water shortage), roots react by increasing their production of abscisic acid (ABA). When abscisic acid is perceived by the leaves, the stomata close to limit water loss through transpiration, which further contributes to limit water [15,16]. Detection of stress by wall sensors leads to reprogramming of gene expression. (part of the design was made with Biorender software, Created with BioRender.com).

Figure 2

Role of transposable elements (TEs) in phenotypic changes and stress responses in fruit trees Structure of TE with LTR (A), non-LTR (B) and of the autonomous and non-autonomous MITE (C). Insertion of a MITE element in the promoter of the MdRNFR1 gene affect its epigenetic and transcriptional status in Apple tree, inducing a reduced ROS accumulation during drought stress [114] (D). Insertion of non-LTR in the intron of the DEF1 gene provoke differential methylation allelic version that impact its transcriptional status and lead to the Mantled fruit phenotype in palm oil [113] (E). Insertion of the TSC1 LTR TE in the promoter of the RUBY gene affect provoke its transcriptional activation under cold stress, provoking the accumulation of anthocyanin in the orange fruit [109] (F).