| Cotton is the most important textile crop in the world. The world’s population is growing fast,however, the available land continues to decline. Improving the acre yield and fiber quality is the onlyway to satisfy the world demands. Upland cotton (Gossypium hirsutum), an allotetraploid variety, is themost widely cultivated cotton species, accounting for95%of production worldwide. Plant height is notonly a determinant factor of plant architecture, but also an essential agronomic trait determining yield.An ideal cotton architecture includes semi-dwarf and shorter lateral branches, which allows a cottonplant to most efficiently use its three dimensional space and to produce the highest yield.Brassinosteriods (BR) is one of the most important factors effecting plant architecture. Sparing in thecotton field and invitro culture of ovules have proved that BR promote fiber elongation, nevertheless,the mechanism of BR regulation of fiber elongation remains elusive. In this paper, we reported ouridentification of a cotton activation-tagged mutant, and described its morphological, genetic,physiological and biochemical characteristics. The gene that caused the dwarf phenotype was clonedusing the T-DNA tag and verifed by transgenic research. The molecular mechanism of BR regulation offiber elongation was explored using the BR-deficiency mutant.1. We isolated the first gain of function mutant of allotetraploid cotton using theactivation-tagging technique. pag1shows extreme dwarfism, wrinkled and dark green leaves,shortened petioles, decreased pollen activity. Histological analysis revealed that cellelongation and expansion were largely reduced in pag1compared to wild-type, whichexplained the dwarfed and compact phenotype. pag1showed a de-etiolated phenotype in thedark, and exogenous application of brassinolide (BL) can rescue the growth of pag1,suggesting that pag1is a BR deficiency mutant but not a BR insensitive mutant.2. Genetic analysis showed that the dwarf phenotype was controlled by one single dominant gene,and co-segregated with the T-DNA tag. Future research proved that activation tag insertupstream of one P450gene and caused its over-expression. Ectopic expression of this gene(PAG1) in Arabidopsis caused severely dwarfed phenotypes, which can be restored by BLtreatment. Just like its homolog CYP734A1, PAG1was also up-regulated by exogenouslyapplied BL and light, which implied that PAG1may catabolize active BRs in a similar manner.3. In the constitutive expression transgenic lines, the plant height is inversely proportional toPAG1expression level, which indicated that manipulation of PAG1expression can be used tocontrol plant height. The transgenic rice lines also showed dwarf stature, which suggested thatPAG1can also be used change monocot crop height. Tissue-specific treatment and grafingexperiment showed that BR can not transport over long distance and green-tissue specificpromoter drived PAG1can reduce the plant height but only slightly effect reproductive tissues,which suggested that Spatiotemporal manipulation of PAG1expression is a promising meansof improving plant architecture. 4. Endogenous levels of BRs are mainly regulated through tissue-specific biosynthesis andcatabolism in order to maintain optimal plant growth and development. PAG1is highlyexpressed at fiber initiation and elongation stage, indicating PAG1play vital role in regulatingfiber development. The fiber of pag1is shorter than wild-type and can BL treatment can rescueits fiber elongation, which suggested that the over-expression of PAG1metabolized active BRsand effected fiber elongation. Transcriptome analysis demonstrated that PAG1plays crucialroles in regulating fiber development via controlling the level of endogenous bioactive BRs,which may affect ethylene signaling cascade by mediating VLCFA. Therefore BR may be avery important regulator of fiber elongation, a role which may be linked to effects on VLCFAbiosynthesis, ethylene signaling, the cell wall, and cytoskeleton-related genes expression. |
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