Rootless with undetectable meristem 1 encodes a monocot‐specific AUX/IAA protein that controls embryonic seminal and post‐embryonic lateral root initiation in maize

Abstract

SUMMARYThe maize (Zea mays L.) rum1-R (rootless with undetectable meristems 1-Reference) mutant does not initiate embryonic seminal roots and post-embryonic lateral roots at the primary root. Map-based cloning revealed that Rum1 encodes a 269 amino acid (aa) monocot-specific Aux/IAA protein. The rum1-R protein lacks 26 amino acids including the GWPPV degron sequence in domain II and part of the bipartite NLS (nuclear localization sequence). Significantly reduced lateral root density (approximately 35%) in heterozygous plants suggests that the rum1-R is a semi-dominant mutant. Overexpression of rum1-R under the control of the maize MSY (Methionine SYnthase) promoter supports this notion by displaying a reduced number of lateral roots (31-37%). Functional characterization suggests that Rum1 is auxin-inducible and encodes a protein that localizes to the nucleus. Moreover, RUM1 is unstable with a half life time of approximately 22 min while the mutant rum1-R protein is very stable. In vitro and in vivo experiments demonstrated an interaction of RUM1 with ZmARF25 and ZmARF34 (Z. mays AUXIN RESPONSE FACTOR 25 and 34). In summary, the presented data suggest that Rum1 encodes a canonical Aux/IAA protein that is required for the initiation of embryonic seminal and post-embryonic lateral root initiation in primary roots of maize.

Molecular interactions of ROOTLESS CONCERNING CROWN AND SEMINAL ROOTS, a LOB domain protein regulating shoot-borne root initiation in maize (Zea maysL.)

“…(f) Transient luciferase expression assays in Arabidopsis protoplasts The effector plasmid containing the GAL4 DNAbinding domain (GAL4DB), and the reporter and reference plasmids containing firefly luciferase (LUC) and renilla LUC were prepared as previously described [35]. The full-length coding sequence of Rtcs (GRMZM2G092542_P01; oligonucleotide primers: Rtcs/Rtcl-LUC-atg-SmaI-fw and Rtcs-LUC-stop-SacIrv) and Rtcl (AC149818.2 FG009; oligonucleotide primers: Rtcs/Rtcl-LUC-atg-SmaI-fw and Rtcl-LUCstop-SacI-rv), and the middle region of ZmARF34 (encoding for aa 377-941, GRMZM2G160005_P01; oligonucleotide primers: ZmArf34_MR-LUC-atgSmaI-fw and ZmArf34_MR-LUC-stop-SacI-rv) were amplified (electronic supplementary material) and subsequently introduced into the SmaI/SacI sites of the effector plasmid.…”

Phloem-associated auxin response maxima determine radial positioning of lateral roots in maize

“…The initiation of lateral roots in maize is not strictly acropetal as in Arabidopsis, and no regularity was found in the sequence of initiation between the different vascular poles [21]. Detailed characterization of the maize rum1 mutant, lacking embryonic seminal roots and lateral roots on the primary root, led to the conclusion that most likely auxin accumulation in the pericycle precedes, and is required for, the degradation of RUM1, a maize Aux/IAA repressor protein [22,23]. Furthermore, auxin availability might also be controlled by RUM1 because rum1 mutants displayed reduced polar auxin transport.…”

Comparative Transcriptome Profiling of Maize Coleoptilar Nodes during Shoot-Borne Root Initiation

“…The rtcs gene is an auxin-inducible early auxin-responsive gene that controls seminal and shoot-borne root formation (Taramino et al, 2007). Similarly, the maize rum1 gene encodes an auxin-inducible early auxin-responsive gene of the Aux/IAA family that is required for seminal and lateral root initiation (von Behrens et al, 2011). In this study, the maize Aux/IAA genes iaa9 and iaa15 were preferentially expressed in wild-type t4 coleoptilar nodes, which might imply a role of these genes in shoot-borne root formation.…”