Aberrant phenotype and transcriptome expression during fiber cell wall thickening caused by the mutation of the Im gene in immature fiber (im) mutant in Gossypium hirsutum L.

Cheng Wang,Wangzhen Guo,Tianzhen Zhang,Yuanda Lv,Wentin Xu

doi:10.1186/1471-2164-15-94

Abstract

BackgroundThe immature fiber (im) mutant of Gossypium hirsutum L. is a special cotton fiber mutant with non-fluffy fibers. It has low dry weight and fineness of fibers due to developmental defects in fiber secondary cell wall (SCW).ResultsWe compared the cellulose content in fibers, thickness of fiber cell wall and fiber transcriptional profiling during SCW development in im mutant and its near-isogenic wild-type line (NIL) TM-1. The im mutant had lower cellulose content and thinner cell walls than TM-1 at same fiber developmental stage. During 25 ~ 35 day post-anthesis (DPA), sucrose content, an important carbon source for cellulose synthesis, was also significantly lower in im mutant than in TM-1. Comparative analysis of fiber transcriptional profiling from 13 ~ 25 DPA indicated that the largest transcriptional variations between the two lines occurred at the onset of SCW development. TM-1 began SCW biosynthesis approximately at 16 DPA, whereas the same fiber developmental program in im mutant was delayed until 19 DPA, suggesting an asynchronous fiber developmental program between TM-1 and im mutant. Functional classification and enrichment analysis of differentially expressed genes (DEGs) between the two NILs indicated that genes associated with biological processes related to cellulose synthesis, secondary cell wall biogenesis, cell wall thickening and sucrose metabolism, respectively, were significantly up-regulated in TM-1. Twelve genes related to carbohydrate metabolism were validated by quantitative reverse transcription PCR (qRT-PCR) and confirmed a temporal difference at the earlier transition and SCW biosynthesis stages of fiber development between TM-1 and im mutant.ConclusionsWe propose that Im is an important regulatory gene influencing temporal differences in expression of genes related to fiber SCW biosynthesis. This study lays a foundation for cloning the Im gene, elucidating molecular mechanism of fiber SCW development and further genetic manipulation for the improvement of fiber fineness and maturity.

Highlights

The immature fiber mutant of Gossypium hirsutum L. is a special cotton fiber mutant with non-fluffy fibers
Decreased cellulose content and thickness of fiber cell wall in im mutant In order to explore possible physiological changes in im mutant caused by the mutation of the Im gene, we compared the cellulose content, a major cell wall component of secondary cell wall (SCW) in fibers between the im mutant and its near-isogenic line (NIL), TM-1, during SCW thickening (Figure 1)
There was no difference between the two lines at 13 and 19 days post-anthesis (DPA), but the im mutant had thinner fiber cell walls (P < 0.001) than TM-1 at 25 DPA and maturity

Summary

Introduction

The immature fiber (im) mutant of Gossypium hirsutum L. is a special cotton fiber mutant with non-fluffy fibers. It has low dry weight and fineness of fibers due to developmental defects in fiber secondary cell wall (SCW). Fiber development consists of four overlapping stages: fiber initiation, fiber elongation, secondary cell wall (SCW) deposition and maturation. Fiber initiation occurs on or near the day of anthesis, but only about 25% of ovular epidermal cells differentiate into the commercially important and spinnable lint fibers. At the late stage of fiber elongation, fibers enter into SCW deposition. The onset of SCW biosynthesis typically occurs from 16 ~ 21 DPA, depending on the cotton species and environmental conditions. Because of the unique characteristics of cotton fiber, it is regarded as an ideal model for studies of plant cell elongation and cell wall biogenesis [3]

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