Date Published: October 1, 2015
Publisher: Public Library of Science
Author(s): Mura Jyostna Devi, Thomas R Sinclair, Earl Taliercio, Ricardo Aroca.
Limiting the transpiration rate (TR) of a plant under high vapor pressure deficit (VPD) has the potential to improve crop yield under drought conditions. The effects of elevated VPD on the expression of genes in the leaves of three soybean accessions, Plant Introduction (PI) 416937, PI 471938 and Hutcheson (PI 518664) were investigated because these accessions have contrasting responses to VPD changes. Hutcheson, a fast-wilting soybean, and PI 471938, a slow-wilting soybean, respond to increased VPD with a linear increase in TR. TR of the slow-wilting PI 416937 is limited when VPD increases to greater than about 2 kPa. The objective of this study was to identify the response of the transcriptome of these accessions to elevated VPD under well-watered conditions and identify responses that are unique to the slow-wilting accessions. Gene expression analysis in leaves of genotypes PI 471938 and Hutcheson showed that 22 and 1 genes, respectively, were differentially expressed under high VPD. In contrast, there were 944 genes differentially expressed in PI 416937 with the same increase in VPD. The increased alteration of the transcriptome of PI 416937 in response to elevated VPD clearly distinguished it from the other slow-wilting PI 471938 and the fast-wilting Hutcheson. The inventory and analysis of differentially expressed genes in PI 416937 in response to VPD is a foundation for further investigation to extend the current understanding of plant hydraulic conductivity in drought environments.
Drought is a major abiotic stress that limits plant growth and drastically reduces crop productivity. Mechanisms that impart tolerance to drought in plants include conservation of soil water through reduced water loss, reduced radiation absorption, reduced leaf area, lower lethal relative water content, deep rooting and lower stomatal conductance [1,2].
Two experiments were conducted to document TR responses of Hutcheson, PI 471938 and PI 416937 to VPD. The samples for transcriptome profiling were collected in the second experiment.
Our results confirmed that high VPD triggers a novel water-conserving transpiration response in PI 416937 and demonstrated that this response was associated with the differential regulation of large numbers of genes. In contrast, the other two soybean genotypes in the study did not exhibit this novel physiological response to VPD, nor did they exhibit the extensive gene regulation found in PI 416937. Transcriptome analysis of genes differentially expressed under high VPD in PI 416937 shows the large quantitative change leads to changes in pathways related to signaling, including TF, signaling proteins and phytohormone metabolism. The changes of signaling pathways in response to high VPD in the slow-wilting accession PI 416937 target changes in processes associated with cell wall development, metabolism and transport, thus highlighting adaptation of PI 416937 to stress. The signals causing changes in cell wall and stomata development possibly affect leaf expansion and stomatal density. Additionally, changes in expression of LEAs and lipid metabolism specific to PI 416937 may stabilize membranes and redirect secondary metabolites to deal with elevated VPD. Particularly interesting are the decreased levels of transcripts encoding water channel proteins. An early response to high VPD by lowering aquaporin levels may reduce demand for water in PI 416937 before the other two genotypes sense a water deficit, resulting in low hydraulic conductivity and water conservation for sustained growth later in the growing season.