Molecular study of drought response in the Mediterranean conifer Pinus pinaster Ait.: Differential transcriptomic profiling reveals constitutive water deficit-independent drought tolerance mechanisms.

Nuria De María,Luís Manuel Díaz,Zhen Li,Miriam López‐Hinojosa,Alberto Pizarro,Pedro Perdiguero,David Sánchez‐Gómez,María Carmen Díaz‐Sala,Célia Miguel,José Antonio Mancha,María Ángeles Guevara,Lieven Sterck,José Antonio Cabezas,María Teresa Cervera,María Dolores Vélez,Carmen Collada

doi:10.1002/ece3.6613

Abstract

Adaptation of long‐living forest trees to respond to environmental changes is essential to secure their performance under adverse conditions. Water deficit is one of the most significant stress factors determining tree growth and survival. Maritime pine (Pinus pinaster Ait.), the main source of softwood in southwestern Europe, is subjected to recurrent drought periods which, according to climate change predictions for the years to come, will progressively increase in the Mediterranean region. The mechanisms regulating pine adaptive responses to environment are still largely unknown. The aim of this work was to go a step further in understanding the molecular mechanisms underlying maritime pine response to water stress and drought tolerance at the whole plant level. A global transcriptomic profiling of roots, stems, and needles was conducted to analyze the performance of siblings showing contrasted responses to water deficit from an ad hoc designed full‐sib family. Although P. pinaster is considered a recalcitrant species for vegetative propagation in adult phase, the analysis was conducted using vegetatively propagated trees exposed to two treatments: well‐watered and moderate water stress. The comparative analyses led us to identify organ‐specific genes, constitutively expressed as well as differentially expressed when comparing control versus water stress conditions, in drought‐sensitive and drought‐tolerant genotypes. Different response strategies can point out, with tolerant individuals being pre‐adapted for coping with drought by constitutively expressing stress‐related genes that are detected only in latter stages on sensitive individuals subjected to drought.

Highlights

Long-living forest trees have developed a unique capacity to respond to environmental changes
We found upregulated genes involved in response to stress and extracellular stimulus, as well as sequence-specific DNA-binding transcription factor activity in sensitive genotypes, while in secondary metabolic process in tolerant genotypes (Figure 3b)
One of the most interesting outcomes of this study was the finding that drought-tolerant genotypes expressed a high number of genes related to stress even before the water deficit took place as opposed with the drought-sensitive genotypes. This finding indicates that constitutive expression of drought-related genes, hormone-regulated genes, genes involved in signaling pathways, as well as those involved in stress protection, can provide functional advantages to cope with an eventual water deficit

Summary

Introduction

Long-living forest trees have developed a unique capacity to respond to environmental changes. Their adaptation and survival under adverse conditions is dependent on essential traits, such as those ones related to drought tolerance. According to recent climate projections, water deficiency will be a recurrent and increasingly acute problem in the Mediterranean area (Cook, Anchukaitis, Touchan, Meko, & Cook, 2016; Cook, Smerdon, Seager, & Coats, 2014; Dubrovský et al, 2014), which will be intensified by decrease in soil water content and evapotranspiration. Paleoclimate field reconstructions estimate that 1998–2012 was the driest 15-year period in this area since 12th century (Cook et al, 2016)

Objectives

Findings

Discussion

Conclusion