Two major quantitative trait loci controlling the number of seminal roots in maize co-map with the root developmental genes rtcs and rum1.

Silvio Salvi,Milena Ouzunova,Silvia Giuliani,Thomas Presterl,Roberto Tuberosa,Marco Maccaferri,Nicola Carraro,Claudia Ricciolini

doi:10.1093/jxb/erw011

Silvio Salvi, Milena Ouzunova + Show 6 more

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https://doi.org/10.1093/jxb/erw011

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Abstract

The genetic dissection of root architecture and functions allows for a more effective and informed design of novel root ideotypes and paves the way to evaluate their effects on crop resilience to a number of abiotic stresses. In maize, limited attention has been devoted to the genetic analysis of root architecture diversity at the early stage. The difference in embryonic (including seminal and primary) root architecture between the maize reference line B73 (which mostly develops three seminal roots) and the landrace Gaspé Flint (with virtually no seminal roots) was genetically dissected using a collection of introgression lines grown in paper rolls and pots. Quantitative trait locus (QTL) analysis identified three QTLs controlling seminal root number (SRN) on chromosome bins 1.02, 3.07, and 8.04-8.05, which collectively explained 66% of the phenotypic variation. In all three cases, Gaspé Flint contributed the allele for lower SRN. Primary root dry weight was negatively correlated with SRN (r= -0.52), and QTLs for primary root size co-mapped with SRN QTLs, suggesting a pleiotropic effect of SRN QTLs on the primary root, most probably caused by competition for seed resources. Interestingly, two out of three SRN QTLs co-mapped with the only two known maize genes (rtcs and rum1) affecting the number of seminal roots. The strong additive effect of the three QTLs and the development of near isogenic lines for each QTL in the elite B73 background provide unique opportunities to characterize functionally the genes involved in root development and to evaluate how root architecture affects seedling establishment, early development, and eventually yield in maize.

Highlights

Roots are highly specialized plant organs playing a vital role in plant growth and adaptation
Primary root dry weight was negatively correlated with seminal root number (SRN) (r= −0.52), and Quantitative trait locus (QTL) for primary root size co-mapped with SRN QTLs, suggesting a pleiotropic effect of SRN QTLs on the primary root, most probably caused by competition for seed resources
Variation in seminal root architecture in a dent×flint type of cross in maize appears to be under oligogenic control, with just three QTLs for number of seminal roots controlling most of the variation

Summary

Introduction

Roots are highly specialized plant organs playing a vital role in plant growth and adaptation. The maize root apparatus comprises the embryonic and the post-embryonic systems, the latter including all shoot-borne roots that are formed at the consecutive shoot nodes as well as. Seminal roots are laid down between 22 d and 40 d after pollination and emerge from the scutellar node at germination contemporaneously or soon after the primary root (Sass, 1977; Erdelska and Videvoncova, 1993; Hochholdinger, 2009). It is not completely clear whether primordia for all seminal roots are differentiated before germination (Feldman, 1994). Seminal roots appear to be a unique feature of maize among Poaceae and, as such, do not develop in sorghum (Singh et al, 2010)

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