Roles of the GLABROUS1 and TRANSPARENT TESTA GLABRA Genes in Arabidopsis Trichome Development

Arabidopsis trichomes are branched, single-celled epidermal hairs. These specialized cells provide a convenient model for investigating the specification of cell fate in plants. Two key genes regulating the initiation of trichome development are GLABROUS1 (GL1) and TRANSPARENT TESTA GLABRA (TTG). GL1 is a member of the myb gene family. The maize R gene, which can functionally complement the Arabidopsis ttg mutation, encodes a basic helix-loop-helix protein. We used constitutively expressed copies of the GL1 and R genes to test hypotheses about the roles of GL1 and TTG in trichome development. The results support the hypothesis that TTG and GL1 cooperate at the same point in the trichome developmental pathway. Furthermore, the constitutive expression of both GL1 and R in the same plant caused trichomes to develop on all shoot epidermal surfaces. Results were also obtained indicating that TTG plays an additional role in inhibiting neighboring cells from becoming trichomes.     

GL3 encodes a bHLH protein that regulates trichome development in arabidopsis through interaction with GL1 and TTG1

Arabidopsis trichome development and differentiation is a well-studied model for plant cell-fate determination and morphogenesis. Mutations in TRANSPARENT TESTA GLABRA1 (TTG1) result in several pleiotropic defects including an almost complete lack of trichomes. The complex phenotype caused by ttg1 mutations is suppressed by ectopic expression of the maize anthocyanin regulator R. Here it is demonstrated that the Arabidopsis trichome development locus GLABRA3 (GL3) encodes an R homolog. GL3 and GLABRA1 (GL1) interact when overexpressed together in plants. Yeast two-hybrid assays indicate that GL3 participates in physical interactions with GL1, TTG1, and itself, but that GL1 and TTG1 do not interact. These data suggest a reiterated combinatorial model for the differential regulation of such diverse developmental pathways as trichome cell-fate determination, root hair spacing, and anthocyanin secondary metabolism.     

Cotton (<Emphasis Type="Italic">Gossypium hirsutum</Emphasis>) JAZ3 and SLR1 function in jasmonate and gibberellin mediated epidermal cell differentiation and elongation

Jasmonate ZIM-domain (JAZ) proteins and DELLA proteins are key negative regulators of jasmonates (JAs) and gibberellin (GA) signaling, respectively. In this study, we found JA and GA synergistically promote fiber cell initiation. We characterized the cellular function of a JAZ protein (GhJAZ3), and a DELLA protein (GhSLR1) of cotton (Gossypium hirsutum). GhJAZ3 is specifically expressed in elongating fibers, while GhSLR1 is expressed in different tissues and at a relatively higher level in 3 DPA ovules. GhSLR1 and GhJAZ3 proteins are localized in the cell nucleus. Yeast two-hybrid analysis indicated that GhSLR1, GhJAZ3 and GhDEL65 could interact with each other, and GhSLR1 could also interact with GhBZR1. Overexpression of GhJAZ3 in Arabidopsis increased hypocotyl and root length, leaf trichome length, and plant height, but decreased the number of leaf trichome, while overexpression of GhSLR1 in Arabidopsis decreased hypocotyl length, leaf trichome length and density. Expression of several leaf trichome initiation determinators (GL3, GL2, TTG2 and MYB23) was down-regulated in GhJAZ3 or GhSLR1 transgenic Arabidopsis, while expression of the cell elongation related genes (EXP1, EXP8, EXPL2 and XTH4) was altered in the GhJAZ3 and GhSLR1 transgenic Arabidopsis. Taken together, these results demonstrate that GhJAZ3 and GhSLR1 function in jasmonate and gibberellin mediated epidermal cell differentiation and elongation.     

Characterization of GhRac1 GTPase expressed in developing cotton (Gossypium hirsutum L.) fibers

Cytoskeleton assembly plays an important role in determining cotton fiber cell length and morphology and is developmentally regulated. As in other plant cells, it is not clear how cytoskeletal assembly in fibers is regulated. Recently, several Rac/Rop GTPases in Arabidopsis were shown to regulate isotropic and polar cell growth of root hairs and pollen tubes by controlling assembly of the cytoskeleton. GhRac1, isolated from cottonseeds, is a member of the Rac/Rop GTPase family and is abundantly expressed in rapidly growing cotton tissues. GhRac1 shows the greatest sequence similarity to the group IV subfamily of Arabidopsis Rac/Rop genes. Overexpression of GhRac1 in E. coli led to the production of a functional GTPase as shown by in vitro enzyme activity assay. In contrast to other Rac/Rop GTPases found in cotton fiber, GhRac1 is highly expressed during the elongation stage of fiber development with expression decreasing dramatically when the rate of fiber elongation declines. The association of highest GhRac1 expression during stages of maximal cotton fiber elongation suggests that GhRac1 GTPase may be a potential regulator of fiber elongation by controlling cytoskeletal assembly.     

拟南芥GLABROUS1两个新等位突变体的筛选和鉴定

植物细胞命运决定机制的解析一直以来都是植物发育生物学研究的核心.模式植物拟南芥的表皮毛形成过程是研究植物细胞命运决定的优良模式系统.为了筛选和鉴定控制拟南芥表皮毛形成的新因子,我们进行了大规模的正向遗传筛选,获得了两株莲座叶表皮毛不能形成或数量显著减少的突变体f08-01和vat002-07.通过对突变基因的克隆和遗传...