Low Mannitol Concentrations in Arabidopsis thaliana Expressing Ectocarpus Genes Improve Salt Tolerance.

Pramod Rathor,Tudor Borza,Yuan Qin,Balakrishnan Prithiviraj,Fabrice Berrue,Yanhui Liu,Thierry Tonon,Sophia Stone,Philippe Potin,Svetlana Yurgel,Joseph P M Hui,Junzeng Zhang,Agnès Groisillier

doi:10.3390/plants9111508

Abstract

Mannitol is abundant in a wide range of organisms, playing important roles in biotic and abiotic stress responses. Nonetheless, mannitol is not produced by a vast majority of plants, including many important crop plants. Mannitol-producing transgenic plants displayed improved tolerance to salt stresses though mannitol production was rather low, in the µM range, compared to mM range found in plants that innately produce mannitol. Little is known about the molecular mechanisms underlying salt tolerance triggered by low concentrations of mannitol. Reported here is the production of mannitol in Arabidopsis thaliana, by expressing two mannitol biosynthesis genes from the brown alga Ectocarpus sp. strain Ec32. To date, no brown algal genes have been successfully expressed in land plants. Expression of mannitol-1-phosphate dehydrogenase and mannitol-1-phosphatase genes was associated with the production of 42.3–52.7 nmol g−1 fresh weight of mannitol, which was sufficient to impart salinity and temperature stress tolerance. Transcriptomics revealed significant differences in the expression of numerous genes, in standard and salinity stress conditions, including genes involved in K+ homeostasis, ROS signaling, plant development, photosynthesis, ABA signaling and secondary metabolism. These results suggest that the improved tolerance to salinity stress observed in transgenic plants producing mannitol in µM range is achieved by the activation of a significant number of genes, many of which are involved in priming and modulating the expression of genes involved in a variety of functions including hormone signaling, osmotic and oxidative stress, and ion homeostasis.

Highlights

Plants are sessile organisms constantly subjected to abiotic stressors such as soil salinity and temperature extremes, which are considered the major limiting factors to agricultural productivity, posing a risk to global food security
EsM1, EsM2 and EsM3, in which selection was done until the 5th generation, was determined by real-time quantitative polymerase chain reaction (Supplementary Table S1)
A microarray study carried out by Chan, Grumet and Loescher [6], at 6 days after the salinity stress (100 mM NaCl), using A. thaliana expressing celery M6PR, found that improved salinity stress tolerance was likely due to differential expression of a variety of genes involved in processes such as salinity and dehydration stress, oxidoreductive processes, sugar and abscisic acid (ABA) metabolism, and cell wall synthesis

Summary

Introduction

Plants are sessile organisms constantly subjected to abiotic stressors such as soil salinity and temperature extremes, which are considered the major limiting factors to agricultural productivity, posing a risk to global food security. Improving plant tolerance to these abiotic factors is critical for agricultural output and environmental sustainability. To achieve tolerance to salinity and drought plants produce different osmolytes including sugar alcohols, proline, polyamines, glycine betaine and proteins from the late embryogenesis abundant (LEA) superfamily [2]. Mannitol is an ubiquitous sugar alcohol found in a wide range of living organisms including bacteria, fungi, algae, and in over 100 plant species, where it serves as a metabolite, osmolyte and anti-oxidant [3,4]. Do not produce mannitol [5]

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