Academic journal article Genetics

The R2R3 MYB Transcription Factor GhMYB109 Is Required for Cotton Fiber Development

Academic journal article Genetics

The R2R3 MYB Transcription Factor GhMYB109 Is Required for Cotton Fiber Development

Article excerpt

ABSTRACT

Cotton (Gossypium hirsutum L.) fibers are single highly elongated cells derived from the outer epidermis of ovules. A large number of genes are required for fiber differentiation and development, but so far, little is known about how these genes control and regulate the process of fiber development. Here we examine the role of the cotton-fiber-specific R2R3 MYB gene GhMYB109 in cotton fiber development. Transgenic reporter gene analysis revealed that a 2-kb GhMYB109 promoter was sufficient to confirm its fiber-specific expression. Antisense-mediated suppression of GhMYB109 led to a substantial reduction in fiber length. Consistently, several genes related to cotton fiber growth were found to be significantly reduced in the transgenic cotton. Our results showed that GhMYB109 is required for cotton fiber development and reveal a largely conserved mechanism of the R2R3 MYB transcription factor in cell fate determination in plants.

COTTON (Gossypium hirsutum L.) is an important economic crop that is extensively used in the textile industry.Cottonfibers aresingle-celledtrichomesderived from epidermal cells of the ovule (Basra and Malik 1984). The fiber development usually consists of four overlappingstages: initiation,primary cell-wall formation, secondary cell-wall formation, and maturation. During theinitial stage,~30%ofepidermalcells (fiber initials)on the ovule surface begin to enlarge and elongate rapidly at or just before anthesis. The primary cell-wall formation starts at anthesis and lasts up to 19-20 days post-anthesis (DPA) (Basra and Malik 1984). The quality and productivity of cotton fibers dependmainly on two biological processes: fiber initiation to determine the number of fibers present on each ovule and fiber elongation to control the final length and strength of each fiber ( John and Keller 1996). Synthesis of the secondary wall initiates ~16 DPA, overlapping with the late primary wall formation,andcontinues for~40DPA, forming a wall (5- 10mmthickness)of almostpurecellulose.Uponmaturity, cotton fibers contain ~90% cellulose. Thus, research of fiber development not only provides a basic understanding of cell differentiation and elongation, but also identifies potential target genes for genetic improvement of cotton fiber production.

Cotton fibers are seed trichomes, which share many similarities with leaf trichomes. Since both the Arabidopsis thaliana trichome and cotton fibers are single-celled structures of epidermal origin, it is likely that Arabidopsis trichomes could serve as a model for elucidating the genetic mechanisms controlling cotton fiber development (Serna and Martin 2006). For the model plant Arabidopsis, trichome development and root epidermal patterning have been studied in depth, and both processes use a common mechanism involving closely related transcription factors and a similar lateral inhibition signaling pathway (Schneider et al. 1997; Schnittger et al. 1999; Larkin et al. 2003). Transcription factors such as the MYB proteins GLABRA1(GL1) or WEREWOLF(WER), the WD40 proteins TRANSPARENT TESTA GLABRA1 (TTG1), andthe basic helix-loop-helix proteinsGLABRA3 (GL3) or ENHANCER OF GLABRA3 (EGL3) appear to form a transcription factor complex to determine epidermal trichome patterning in Arabidopsis (Glover 2000; Schiefelbein 2003; Hulskamp 2004; Ramsay and Glover 2005; Serna and Martin 2006). This complex is thought to regulate the homeodomain leucine zipper protein GLABRA2 (GL2) and a small family of singlerepeat MYB proteins lacking the transcription activation domains TRIPTYCHON (TRY), CAPRICE (CPC), and ENHANCEROFTRYANDCPC1 (ETC1). GL2 encodes a homeobox (HOX) transcription factor that promotes trichome cell differentiation and growth (Rerie et al. 1994; Szymanski et al. 1998; Ohashi et al. 2002). The single-repeat MYB proteins TRY, ETC1, and ETC2 have been shown tonegatively regulate trichome formation and act in a partially redundant manner to mediate the lateral inhibition (Schnittger et al. …

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