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Title: Molecular Analysis of SCARECROW Genes Expressed in White Lupin Cluster Roots

item Bucciarelli, Bruna
item Miller, Susan - Sue
item Vance, Carroll

Submitted to: Journal of Experimental Botany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/24/2009
Publication Date: 3/1/2010
Citation: Sbabou, L., Bucciarelli, B., Miller, S.S., Liu, J., Brhada, F., Filali-Maltouf, A., Allan, D., Vance, C.P. 2010. Molecular Analysis of SCARECROW Genes Expressed in White Lupin Cluster Roots. Journal of Experimental Botany. 61(5):1351-1363.

Interpretive Summary: Phosphorus (P) is one of the primary limiting nutrients required for plant growth. Phosphorus deficiency in crop land is remediated by adding P fertilizer. The use of P fertilizer is expensive and can result in pollution of rivers and streams. Some plants, like white lupin, have novel root adaptations for acquiring scarce P. Lupins, when growing in low P, form many extensive complex roots called cluster roots. Lupin cluster roots increase root volume and surface area 100-fold allowing for more exploration of soil for nutrients. Lupin cluster roots also exude many chemical compounds that help solubilize bound P in soils. The objective of this research was to identify genes that control cluster root formation. In this work we identify two genes known as scarecrow. These genes are highly similar in sequence and function. We show that the expression of scarecrow genes is correlated with cluster root development but not with P deficiency. Using a special technique we blocked the expression of scarecrow genes. When scarecrow gene expression is blocked, cluster root formation is inhibited but not completely stopped. Manipulation of scarecrow genes through biotechnology may be useful to other crops in forming more roots.

Technical Abstract: The Scarecrow (SCR) transcription factor plays a crucial role in root cell radial patterning and is required for maintenance of the quiescent center and differentiation of the endodermis. In response to phosphorus (P) deficiency, white lupin (Lupinus albus L.) root surface area increases some 50- to 70-fold due to the development of cluster (proteoid) roots. Previously we reported that SCR-like ESTs were expressed during cluster root development. Here we report the cloning of two white lupin SCR genes, LaSCR1 and LaSCR2. The predicted amino acid sequence of both LaSCRs 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 qRT-PCR and RNA gel hybridization indicated that the two LaSCRs are expressed predominantly in roots. Expression of LaSCRs was not directly responsive to 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 delivered through Agrobacterium rhizogenes resulted in decreased root numbers and mass reflecting the potential role of LaSCR1 in maintaining root growth in these species. Our results suggest we have characterized functional orthologs of AtSCR.