AtWuschel Promotes Formation of the Embryogenic Callus in Gossypium hirsutum

Abstract

Upland cotton (Gossypium hirsutum) is one of the most recalcitrant species for in vitro plant regeneration through somatic embryogenesis. Callus from only a few cultivars can produce embryogenic callus (EC), but the mechanism is not well elucidated. Here we screened a cultivar, CRI24, with high efficiency of EC produce. The expression of genes relevant to EC production was analyzed between the materials easy to or difficult to produce EC. Quantitative PCR showed that CRI24, which had a 100% EC differentiation rate, had the highest expression of the genes GhLEC1, GhLEC2, and GhFUS3. Three other cultivars, CRI12, CRI41, and Lu28 that formed few ECs expressed these genes only at low levels. Each of the genes involved in auxin transport (GhPIN7) and signaling (GhSHY2) was most highly expressed in CRI24, with low levels in the other three cultivars. WUSCHEL (WUS) is a homeodomain transcription factor that promotes the vegetative-to-embryogenic transition. We thus obtained the calli that ectopically expressed Arabidopsis thaliana Wus (AtWus) in G. hirsutum cultivar CRI12, with a consequent increase of 47.75% in EC differentiation rate compared with 0.61% for the control. Ectopic expression of AtWus in CRI12 resulted in upregulation of GhPIN7, GhSHY2, GhLEC1, GhLEC2, and GhFUS3. AtWus may therefore increase the differentiation potential of cotton callus by triggering the auxin transport and signaling pathways.

Identification of Polycomb Repressive Complex1, Trithorax group genes and their simultaneous expression with WUSCHEL, WUSCHEL-related Homeobox5 and SHOOT MERISTEMLESS during the induction phase of somatic embryogenesis in Medicago truncatula Gaertn.

“…Su et al (2009) showed the correct WUS expression, controlled by an appropriate exogenous auxin level, to be crucial for the Arabidopsis somatic embryo formation. AtWUS was demonstrated to enhance the conversion of non-embryogenic cells to embryogenic ones during SE in Gossypium hirsutum (Zheng et al 2014). All the results discussed above may indicate that WUS expression takes place early during SE, the expression profile being dependent on the composition of hormones and their concentration in the medium.…”

“…Ectopic expression of AtWUS in Coffea canephora induces callus formation and causes an increase in somatic embryos production (Arroyo-Herrera et al 2008). An identical ectopic expression in Gossypium hirsutum WUS promotes the vegetative-to-embryogenic transition (Zheng et al 2014). Chen et al (2009) investigated WUS and additionally WOX5 and found WUS expression to be essential for M. truncatula callus growth and somatic embryo induction.…”

Current Perspectives on the Auxin-Mediated Genetic Network that Controls the Induction of Somatic Embryogenesis in Plants

“…An SE-promoting capacity was also indicated for WUSCHEL (WUS), which is a member of the WOX superfamily of the genes encoding the plant-specific homeobox TFs that are involved in promoting cell division and/or preventing the premature cell differentiation of the stem cells in SAM (reviewed in [155,156]). The positive impact of WUS on the embryogenic potential of tissue was indicated given that the gain-of-function mutation in WUS led to the spontaneous formation of somatic embryos on Arabidopsis root explants [157] and an overexpression of WUS promoted or enhanced the embryogenic response in other plants [158][159][160]. Auxin treatment was found to be essential for correctly regulating the WUS expression and the WUS transcripts that were detected in a group of embryogenic callus cells were postulated to indicate an auxin accumulation in the SAM and the pro-embryo [103].…”

Somatic Embryogenesis: Fundamental Aspects and Applications

“…Few studies involving a genetic transformation in annatto have been performed, including direct and indirect somatic embryogenesis-based transformation system (Parimalan et al 2011) and transient transformation from hypocotyls (Zaldívar- Cruz et al 2003), all mediated by Agrobacterium tumefaciens. On top of that, there is a growing body of literature that reports the usefulness of the embryogenic pathway in genetic transformation protocols Bull et al 2009;Yang et al 2014;. Somatic embryogenesis is a unique system that has also become an appropriate method for studying the morphophysiological and molecular aspects of cell differentiation.…”