Molecular analysis of SCARECROW genes expressed in white lupin cluster roots

Abstract

The Scarecrow (SCR) transcription factor plays a crucial role in root cell radial patterning and is required for maintenance of the quiescent centre and differentiation of the endodermis. In response to phosphorus (P) deficiency, white lupin (Lupinus albus L.) root surface area increases some 50-fold to 70-fold due to the development of cluster (proteoid) roots. Previously it was reported that SCR-like expressed sequence tags (ESTs) were expressed during early cluster root development. Here the cloning of two white lupin SCR genes, LaSCR1 and LaSCR2, is reported. The predicted amino acid sequences of both LaSCR gene products are highly similar to AtSCR and contain C-terminal conserved GRAS family domains. LaSCR1 and LaSCR2 transcript accumulation localized to the endodermis of both normal and cluster roots as shown by in situ hybridization and gene promoter::reporter staining. Transcript analysis as evaluated by quantitative real-time-PCR (qRT-PCR) and RNA gel hybridization indicated that the two LaSCR genes are expressed predominantly in roots. Expression of LaSCR genes was not directly responsive to the P status of the plant but was a function of cluster root development. Suppression of LaSCR1 in transformed roots of lupin and Medicago via RNAi (RNA interference) delivered through Agrobacterium rhizogenes resulted in decreased root numbers, reflecting the potential role of LaSCR1 in maintaining root growth in these species. The results suggest that the functional orthologues of AtSCR have been characterized.

Update on White Lupin Cluster Root Acclimation to Phosphorus Deficiency Update on Lupin Cluster Roots

“…Evidence suggested that PDR2 is imperative for maintaining SCR protein during P starvation. White lupin SCRs (LaSCR1 and LaSCR2) have been isolated and recently characterized (Sbabou et al, 2010). Consistent with the localization of SCR genes in all the species examined to date (Pysh et al, 1999;Sassa et al, 2001;Kamiya et al, 2003;Laajanen et al, 2007), the expression of LaSCR genes has been localized to the root endodermis and quiescent center and seems to be closely related to cluster root development rather than to the P status of the plant.…”

“…Consistent with the localization of SCR genes in all the species examined to date (Pysh et al, 1999;Sassa et al, 2001;Kamiya et al, 2003;Laajanen et al, 2007), the expression of LaSCR genes has been localized to the root endodermis and quiescent center and seems to be closely related to cluster root development rather than to the P status of the plant. Suppression of LaSCR1 transcripts in transgenic lupin roots resulted in reduced cluster root numbers, implying a role for LaSCR1 in maintaining root growth in white lupin (Sbabou et al, 2010).…”

Molecular characterization of SCARECROW (CsSCR) gene expressed during somatic embryo development and in root of cucumber (Cucumis sativus L.)

“…Southern blot analysis using a molecular probe specific to a region encoding a conserved domain confirmed that there are no closely related paralogues of the CsSCR gene in the cucumber genome. This is in contrast to white lupin, in which two highly similar SCS genes, that play a role during cluster root development, were identified (Sbabou et al 2010).…”

“…SCR is involved in root radial patterning in A. thaliana (Di Laurenzio et al 1996;Benfey et al 1993;Scheres et al 1995), and the expression patterns of AtSCR orthologues can suggest a similar function in maize (Lim et al 2000(Lim et al , 2005, pea (Sassa et al 2001), rice (Kamiya et al 2003), Pinus sylvestris (Laajanen et al 2007) and white lupin (Sbabou et al 2010). In A. thaliana, SCR and another GRAS family member SHR (SHORT ROOT) play a key role in specification of the cortex and endodermis cell layers, which are located between the epidermis and the pericycle.…”

<i>Peanut stunt virus</i>-induced gene silencing in white lupin (<i>Lupinus albus</i>)

“…White lupin plants are recalcitrant to stable transformation: Agrobacterium tumefaciens-mediated transformation has not been successful so far. Transformed-hairy roots induced by the infection of A. rhizogenes have been used to elucidate the functions of endogenous genes (Cheng et al 2011a;Sbabou et al 2010;Uhde-Stone et al 2005), although shoots cannot be regenerated from hairy roots. Thus, genetic transformation is of limited use for the study of white lupin genes, especially those expressed in shoots.…”