Abstract

   Fuzzless-lintless mutant (fl) ovules of upland cotton have been used to
   investigate cotton fiber development for decades. However, the
   molecular differences of green tissues between fl and wild-type (WT)
   cotton were barely reported. Here, we found that gossypol content, the
   most important secondary metabolite of cotton leaves, was higher in
   Gossypium hirsutum L. cv Xuzhou-142 (Xu142) WT than in fl. Then, we
   performed comparative proteomic analysis of the leaves from Xu142 WT
   and its fl. A total of 4506 proteins were identified, of which 103 and
   164 appeared to be WT- and fl-specific, respectively. In the 4239
   common-expressed proteins, 80 and 74 were preferentially accumulated in
   WT and fl, respectively. Pathway enrichment analysis and
   protein–protein interaction network analysis of both variety-specific
   and differential abundant proteins showed that secondary metabolism and
   chloroplast-related pathways were significantly enriched. Quantitative
   real-time PCR confirmed that the expression levels of 12 out of 16
   selected genes from representative pathways were consistent with their
   protein accumulation patterns. Further analyses showed that the content
   of chlorophyll a in WT, but not chlorophyll b, was significantly
   increased compared to fl. This work provides the leaf proteome profiles
   of Xu142 and its fl mutant, indicating the necessity of further
   investigation of molecular differences between WT and fl leaves.

   Keywords: proteomics, cotton leaves, fuzzless-lintless mutant,
   gossypol, chlorophyll

1. Introduction

   Upland cotton provides the major source of natural fiber materials for
   the textile industry. Cotton fiber is a single-cell trichome derived
   from the seed epidermis, and thus is commonly used as an ideal model to
   investigate plant cell elongation [[34]1]. The development of the
   cotton fiber cell is commonly defined as four distinct and overlapping
   stages: fiber initiation, fast elongation, secondary wall biosynthesis,
   and maturation [[35]2]. Cotton fibers are also characterized as two
   types: fuzz and lint. Fuzz fibers are initiated after 5 days post
   anthesis and are shorter than 5 mm at the maturation stage [[36]3].
   Lint fibers form the major part used for textile products, initiating
   before the day of anthesis and finally forming the mature long fibers
   [[37]4]. To investigate essential molecular events for regulating
   cotton fiber development, fuzzless and/or lintless mutants for fiber
   have been used as negative references for a long time. Many functional