Fenglin Deng

A thaumatin-like protein gene involved in cotton fiber secondary cell wall development enhances resistance against Verticillium dahliae and other stresses in transgenic tobacco.

For the first time, a sea-island cotton (Gossypium barbadense L.) thaumatin-like protein gene (GbTLP1) with a potential role in secondary cell wall development has been overexpressed in tobacco to elucidate its function. The presence of the transgene was verified by Southern blotting and higher expression levels of GbTLP1 in transgenic tobacco plants were revealed by reverse-transcription and quantitative real-time polymerase chain reaction analyses. Transgenic plants with constitutively higher expression of the GbTLP1 showed enhanced resistance against different stress agents, particularly, its performance against Verticillium dahliae was exceptional. Transgenic tobacco plants also exhibited considerable resistance against Fusarium oxysporum and some abiotic stresses including salinity and drought. In this experiment, transgenic plants without GbTLP1 expression were also used as controls, which behaved similar to non-transgenic control plants. Overexpression of GbTLP1 had no significant deleterious effect on plant growth except that flowering was delayed for 3-5 weeks. The apparent pleiotropic effect of this novel gene has given us insight to the plant defense mechanism.

GbTCP, a cotton TCP transcription factor, confers fibre elongation and root hair development by a complex regulating system

As the most important natural raw material for textile industry, cotton fibres are an excellent model for studying single-cell development. Although expression profiling and functional genomics have provided some data, the mechanism of fibre development is still not well known. A class I TCP transcription factor (designated GbTCP), encoding 344 amino acids, was isolated from the normalized cDNA library of sea-island cotton fibre (from –2 to 25 days post anthesis). GbTCP was preferentially expressed in the elongating cotton fibre from 5 to 15 days post anthesis. Some expression was also observed in stems, apical buds, and petals. RNAi silencing of GbTCP produced shorter fibre, a reduced lint percentage, and a lower fibre quality than the wild-type plants. Overexpression of GbTCP enhanced root hair initiation and elongation in Arabidopsis and regulated branching. Solexa sequencing and Affymetrix GeneChip analysis indicated that GbTCP positively regulates the level of jasmonic acid (JA) and, as a result, activates downstream genes (reactive oxygen species, calcium signalling, ethylene biosynthesis and response, and several NAC and WRKY transcription factors) necessary for elongation of fibres and root hairs. JA content analysis in cotton also confirmed that GbTCP has a profound effect on JA biosynthesis. In vitro ovule culture showed that an appropriate concentration of JA promoted fibre elongation. The results suggest that GbTCP is an important transcription factor for fibre and root hair development by regulating JA biosynthesis and response and other pathways, including reactive oxygen species, calcium channel and ethylene signalling.

A Genetic and Metabolic Analysis Revealed that Cotton Fiber Cell Development Was Retarded by Flavonoid Naringenin

Flavonoids and flavenoid synthesis affect white cotton fiber development. The cotton (Gossypium spp.) fiber is a unique elongated cell that is useful for investigating cell differentiation. Previous studies have demonstrated the importance of factors such as sugar metabolism, the cytoskeleton, and hormones, which are commonly known to be involved in plant cell development, while the secondary metabolites have been less regarded. By mining public data and comparing analyses of fiber from two cotton species (Gossypium hirsutum and Gossypium barbadense), we found that the flavonoid metabolism is active in early fiber cell development. Different flavonoids exhibited distinct effects on fiber development during ovule culture; among them, naringenin (NAR) could significantly retard fiber development. NAR is a substrate of flavanone 3-hydroxylase (F3H), and silencing the F3H gene significantly increased the NAR content of fiber cells. Fiber development was suppressed following F3H silencing, but the overexpression of F3H caused no obvious effects. Significant retardation of fiber growth was observed after the introduction of the F3H-RNA interference segment into the high-flavonoid brown fiber G. hirsutum T586 line by cross. A greater accumulation of NAR as well as much shorter fibers were also observed in the BC1 generation plants. These results suggest that NAR is negatively associated with fiber development and that the metabolism mediated by F3H is important in fiber development, thus highlighting that flavonoid metabolism represents a novel pathway with the potential for cotton fiber improvement.

GbPDF1 Is Involved in Cotton Fiber Initiation via the Core cis-Element HDZIP2ATATHB2

Cotton (Gossypium spp.) fiber cells are seed trichomes derived from the epidermal layer of the cotton seed coat. The molecular components responsible for regulating fiber cell differentiation have not been fully elucidated. A cotton PROTODERMAL FACTOR1 gene (GbPDF1) was found to be expressed preferentially during fiber initiation and early elongation, with highest accumulation in fiber cells 5 d post anthesis. PDF1 silencing caused retardation of fiber initiation and produced shorter fibers and lower lint percentage compared with the wild type, indicating that the gene is required for cotton fiber development. Further analysis showed that a higher accumulation of hydrogen peroxide occurred in the RNA interference transgenic cotton lines. Meanwhile, the expression of several genes related to ethylene and pectin synthesis or sugar transport during cotton fiber growth was found to be significantly reduced in the PDF1-suppressed cotton. Three proteins interacting with GbPDF1 in yeast and in planta might involve cellular signaling or metabolism. GbPDF1 promoter::GUS constructs in transgenic cotton were predominantly expressed in the epidermis of ovules and developing fibers. Progressive deletions of the GbPDF1 promoter showed that a 236-bp promoter fragment was sufficient for basal GbPDF1 transcription in cotton. Mutation of putative regulatory sequences showed that HDZIP2ATATHB2, an element within the fragment, was essential for PGbPDF1-1 expression. The binding activity between this cis-element and nuclear extracts from fiber-bearing cotton ovules at 5 d post anthesis was specific. We conclude that GbPDF1 plays a critical role together with interaction partners in hydrogen peroxide homeostasis and steady biosynthesis of ethylene and pectin during fiber development via the core cis-element HDZIP2ATATHB2.

Suppression of GhAGP4 gene expression repressed the initiation and elongation of cotton fiber.

Cotton fibers, important natural raw materials for the textile industry, are trichomes elongated from epidermal cells of cotton ovules. To date, a number of genes have been shown to be critical for fiber development. In this study, the roles of genes encoding fasciclin-like arabinoglactan proteins (FLAs) in cotton fiber were examined by transforming RNA interfering (RNAi) construct. The RNAi according to the sequence of GhAGP4 caused a significant reduction of its mRNA level, and the expression of other three FLAs (GhAGP2, GhAGP3, GhFLA1) were also partially suppressed. The fiber initiation and fiber elongation were inhibited in the transgenic plants. As for the mature fibers of transgenic cotton, the fiber length became significantly shorter and the fiber quality became worse. In addition, the RNAi of GhAGP4 also affected the cytoskeleton network and the cellulose deposition of fiber cells. Through ovule culture, it was found that the expression of cotton FLA genes were upregulated by GA3, especially for GhAGP2 and GhAGP4. These results indicate that the FLAs are essential for the initiation and elongation of cotton fiber development.

The calcium sensor GhCaM7 promotes cotton fiber elongation by modulating reactive oxygen species (ROS) production

Fiber elongation is the key determinant of fiber quality and output in cotton (Gossypium hirsutum). Although expression profiling and functional genomics provide some data, the mechanism of fiber development is still not well understood. Here, a gene encoding a calcium sensor, GhCaM7, was isolated based on its high expression level relative to other GhCaMs in fiber cells at the fast elongation stage. The level of expression of GhCaM7 in the wild-type and the fuzzless/lintless mutant correspond to the presence and absence, respectively, of fiber initials. Overexpressing GhCaM7 promotes early fiber elongation, whereas GhCaM7 suppression by RNAi delays fiber initiation and inhibits fiber elongation. Reactive oxygen species (ROS) play important roles in early fiber development. ROS induced by exogenous hydrogen peroxide (H2 O2 ) and Ca(2+) starvation promotes early fiber elongation. GhCaM7 overexpression fiber cells show increased ROS concentrations compared with the wild-type, while GhCaM7 RNAi fiber cells have reduced concentrations. Furthermore, we show that H2 O2 enhances Ca(2+) influx into the fiber and feedback-regulates the expression of GhCaM7. We conclude that GhCaM7, Ca(2+) and ROS are three important regulators involved in early fiber elongation. GhCaM7 might modulate ROS production and act as a molecular link between Ca(2+) and ROS signal pathways in early fiber development.