Changes in Transcript Related to Osmosis and Intracellular Ion Homeostasis in Paulownia tomentosa under Salt Stress

Abstract

Paulownia tomentosa is an important economic and greening tree species that is cultivated widely, including salt environment. Our previous studies indicated its autotetraploid induced by colchicine showed better stress tolerance, but the underlying molecular mechanism related to ploidy and salt stress is still unclear. To investigate this issue, physiological measurements and transcriptome profiling of diploid and autotetraploid plants untreated and treated with NaCl were performed. Through the comparisons among four accessions, for one thing, we found different physiological changes between diploid and autotetraploid P. tomentosa; for another, and we detected many differentially expressed unigenes involved in salt stress response. These differentially expressed unigenes were assigned to several metabolic pathways, including "plant hormone signal transduction," "RNA transporter," "protein processing in endoplasmic reticulum," and "plant-pathogen interaction," which constructed the complex regulatory network to maintain osmotic and intracellular ion homeostasis. Quantitative real-time polymerase chain reaction was used to confirm the expression patterns of 20 unigenes. The results establish the foundation for the genetic basis of salt tolerance in P. tomentosa, which in turn accelerates Paulownia breeding and expands available arable land.

Keywords: autotetraploid Paulownia tomentosa; ion homeostasis; osmotic homeostasis; salt stress; transcriptome sequencing.

Figure 1

The length distribution of the coding sequence.

Figure 2

(A) The differently expressed unigenes in PT4 vs. PT2, PT4S vs. PT2S PT2S vs. PT4S and PT4S vs. PT4. (B) The differential consistently expressed unigenes among four comparisons.

Figure 3

The differentially expressed unigenes in two comparisons PT2S vs. PT2 and PT4S vs. PT4. Two thousand one hundred sixty-six differentially expressed unigenes were clustered into eight categories according to their expression patterns.

Figure 4

The consistently differential expression unigenes from four comparisons were enriched in GO terms.

Figure 5

Quantitative Real-Time PCR (qRT-PCR) analysis of 20 selected differentially expressed unigenes. 18S rRNA was used as the internal reference gene. For each group, the PT2(S-0) expression level was considered as 1.00, and other samples were normalized accordingly. Standard error of the mean for three technical replicates is represented by the error bars. S-0, 0 day, 70 mM salt-treated for PT2, and PT4; S-5, 5 days, 70 mM salt-treated for PT2 and PT4; S-10, 10 days, 70 mM salt-treated for PT2, and PT4; S-15, 15 days, 70 mM salt-treated for PT2, and PT4; S-20, 20 days, 70 mM salt-treated for PT2, and PT4.