Transcriptomic analysis of salt stress responsive genes in Rhazya stricta.

Nahid H Hajrah,Ahmed Atef,Sherif Edris,Fotouh M El-Domyati,Jamal S M Sabir,Rania M Makki,Charllotte A Nelson,Ahmed M Ramadan,Ahmed Bahieldin,Nour O Gadalla,Mohammad A Khiyami,Abdullah Y Obaid,Neil Hall,Dhivya Arasappan,Madgy A Al-Kordy,Mohammed Z Mutwakil,Robert K Jansen,Alawia Alhebshi

doi:10.1371/journal.pone.0177589

Abstract

Rhazya stricta is an evergreen shrub that is widely distributed across Western and South Asia, and like many other members of the Apocynaceae produces monoterpene indole alkaloids that have anti-cancer properties. This species is adapted to very harsh desert conditions making it an excellent system for studying tolerance to high temperatures and salinity. RNA-Seq analysis was performed on R. stricta exposed to severe salt stress (500 mM NaCl) across four time intervals (0, 2, 12 and 24 h) to examine mechanisms of salt tolerance. A large number of transcripts including genes encoding tetrapyrroles and pentatricopeptide repeat (PPR) proteins were regulated only after 12 h of stress of seedlings grown in controlled greenhouse conditions. Mechanisms of salt tolerance in R. stricta may involve the upregulation of genes encoding chaperone protein Dnaj6, UDP-glucosyl transferase 85a2, protein transparent testa 12 and respiratory burst oxidase homolog protein b. Many of the highly-expressed genes act on protecting protein folding during salt stress and the production of flavonoids, key secondary metabolites in stress tolerance. Other regulated genes encode enzymes in the porphyrin and chlorophyll metabolic pathway with important roles during plant growth, photosynthesis, hormone signaling and abiotic responses. Heme biosynthesis in R. stricta leaves might add to the level of salt stress tolerance by maintaining appropriate levels of photosynthesis and normal plant growth as well as by the participation in reactive oxygen species (ROS) production under stress. We speculate that the high expression levels of PPR genes may be dependent on expression levels of their targeted editing genes. Although the results of PPR gene family indicated regulation of a large number of transcripts under salt stress, PPR actions were independent of the salt stress because their RNA editing patterns were unchanged.

Highlights

Plant species have developed a series of mechanisms to adjust to environmental stresses [1, 2, 3]
Sequencing of cDNA samples of R. stricta leaves under control conditions and salt stress (500 mM NaCl) treatments across time (0–24 h) yielded 86–154 million reads corresponding to an average of ~10 billion nucleotides of cDNA per sample (Table 1)
We can conclude that the wild plant species R. stricta harbors several mechanisms for avoiding protein misfolding, aggregation or denaturation and the efficient production of several key secondary metabolites and reactive oxygen species (ROS) that helps the plant to withstand salt stress

Summary

Introduction

Plant species have developed a series of mechanisms to adjust to environmental stresses [1, 2, 3] These mechanisms act as regulatory networks of genes and pathways that crosstalk in order to cope with stress. Several enzymes in the porphyrin and chlorophyll metabolism pathway are key players in the production of tetrapyrroles that maintain stay-green performance of wild plant species under adverse environmental conditions like drought and salinity. These enzymes involve 5-aminolevulinic acid (ALA) dehydratase, porphobilinogen deaminase, coproporphyrinogen III oxidase, protoporphyrinogen IX oxidase, Mg-protoporphyrin IX chelatase and protochlorophyllide oxidoreductase

Methods

Results

Conclusion