# Sphingosine Promotes Fiber Early Elongation in Upland Cotton

## TL;DR

This study shows that sphingosine promotes early fiber elongation in cotton, while myriocin inhibits it, and identifies key sphingolipid metabolites and gene pathways involved.

## Contribution

The novel finding is that specific sphingolipids like dihydrosphingosine and phytosphingosine promote cotton fiber elongation through changes in sphingolipid metabolism and gene expression.

## Key findings

- Phytosphingosine (PHS) promotes cotton fiber elongation in a dose-dependent manner.
- PHS treatment alters the levels of 22 sphingolipids and affects 432 genes, including those in the phenylpropanoid biosynthesis pathway.
- Auxin-related genes are up-regulated, while auxin metabolite levels are reduced in PHS-treated fibers.

## Abstract

Sphingolipids play an important role in cotton fiber development, but the regulatory mechanism is largely unclear. We found that serine palmitoyltransferase (SPT) enzyme inhibitors, myriocin and sphingosine (dihydrosphingosine (DHS) and phytosphingosine (PHS)), affected early fiber elongation in cotton, and we performed a sphingolipidomic and transcriptomic analysis of control and PHS-treated fibers. Myriocin inhibited fiber elongation, while DHS and PHS promoted it in a dose–effect manner. Using liquid chromatography–tandem mass spectrometry (LC–MS/MS), we found that contents of 22 sphingolipids in the PHS-treated fibers for 10 days were changed, of which the contents of 4 sphingolipids increased and 18 sphingolipids decreased. The transcriptome analysis identified 432 differentially expressed genes (238 up-regulated and 194 down-regulated) in the PHS-treated fibers. Among them, the phenylpropanoid biosynthesis pathway is the most significant enrichment. The expression levels of transcription factors such as MYB, ERF, LBD, and bHLH in the fibers also changed, and most of MYB and ERF were up-regulated. Auxin-related genes IAA, GH3 and BIG GRAIN 1 were up-regulated, while ABPs were down-regulated, and the contents of 3 auxin metabolites were decreased. Our results provide important sphingolipid metabolites and regulatory pathways that influence fiber elongation.