Abstract
The quality of cotton fiber is determined by its final length and strength, which is a function of primary and secondary cell wall deposition. Using a comparative proteomics approach, we identified 104 proteins from cotton ovules 10 days postanthesis with 93 preferentially accumulated in the wild type and 11 accumulated in the fuzzless-lintless mutant. Bioinformatics analysis indicated that nucleotide sugar metabolism was the most significantly up-regulated biochemical process during fiber elongation. Seven protein spots potentially involved in pectic cell wall polysaccharide biosynthesis were specifically accumulated in wild-type samples at both the protein and transcript levels. Protein and mRNA expression of these genes increased when either ethylene or lignoceric acid (C24:0) was added to the culture medium, suggesting that these compounds may promote fiber elongation by modulating the production of cell wall polymers. Quantitative analysis revealed that fiber primary cell walls contained significantly higher amounts of pectin, whereas more hemicellulose was found in ovule samples. Significant fiber growth was observed when UDP-L-rhamnose, UDP-D-galacturonic acid, or UDP-D-glucuronic acid, all of which were readily incorporated into the pectin fraction of cell wall preparations, was added to the ovule culture medium. The short root hairs of Arabidopsis uer1-1 and gae6-1 mutants were complemented either by genetic transformation of the respective cotton cDNA or by adding a specific pectin precursor to the growth medium. When two pectin precursors, produced by either UDP-4-keto-6-deoxy-D-glucose 3,5-epimerase 4-reductase or by UDP-D-glucose dehydrogenase and UDP-D-glucuronic acid 4-epimerase successively, were used in the chemical complementation assay, wild-type root hair lengths were observed in both cut1 and ein2-5 Arabidopsis seedlings, which showed defects in C24:0 biosynthesis or ethylene signaling, respectively. Our results suggest that ethylene and C24:0 may promote cotton fiber and Arabidopsis root hair growth by activating the pectin biosynthesis network, especially UDP-L-rhamnose and UDP-D-galacturonic acid synthesis.
Highlights
The quality of cotton fiber is determined by its final length and strength, which is a function of primary and secondary cell wall deposition
Our results suggest that ethylene and C24:0 may promote cotton fiber and Arabidopsis root hair growth by activating the pectin biosynthesis network, especially UDP-L-rhamnose and UDP-D-galacturonic acid synthesis
Using cDNA microarray hybridization data obtained from 11,692 cotton fiber UniESTs, we previously identified 778 cDNAs that are preferentially expressed during the fast fiber elongation period [7]
Summary
Plant Materials—Upland cotton (G. hirsutum L. cv. Xuzhou 142) and the fuzzless-lintless (fl) mutant, originally discovered in the Xuzhou 142 cotton field in China [16], were grown in an artificial soil mixture in fully climate-controlled walk-in growth chambers. Identification of Fiber-preferential Biochemical Pathways—The software KOBAS, which stands for Kyoto Encyclopedia of Genes and Genomes (KEGG) Orthology-based Annotation System [26], was used to identify biochemical reactions involved in cotton fiber development and to calculate the statistical significance of each step This program assigns a given set of genes to pathways by first matching the genes to similar genes (as determined by a BLAST similarity search with cutoff E values Ͻ1 ϫ 10Ϫ6, rank Ͻ5, and sequence identity Ͼ55%) in known pathways in the KEGG database. HPLC Separation and GC/MS Identification—The water-soluble fractions obtained above were filtered with 0.22-m filters (Millipore) and analyzed on an HPLC1200 series instrument (Agilent Technologies) at 40 °C using a ZORBAX Eclipse XDB-C18 column (0.46 ϫ 15 cm; Agilent Technologies), monitored using a UV detector at 254 nm [32], and further identified by GC/MS as specified in the Analysis of Cell Wall Monosaccharide Composition section. Statistical Analysis—Whenever applicable, all data were evaluated by one-way analysis of variance software combined with Tukey’s test to obtain p values
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