Isolation, Characterization, and Pericycle-Specific Transcriptome Analyses of the Novel Maize Lateral and Seminal Root Initiation Mutant rum1

Abstract

The monogenic recessive maize (Zea mays) mutant rootless with undetectable meristems 1 (rum1) is deficient in the initiation of the embryonic seminal roots and the postembryonic lateral roots at the primary root. Lateral root initiation at the shoot-borne roots and development of the aerial parts of the mutant rum1 are not affected. The mutant rum1 displays severely reduced auxin transport in the primary root and a delayed gravitropic response. Exogenously applied auxin does not induce lateral roots in the primary root of rum1. Lateral roots are initiated in a specific cell type, the pericycle. Cell-type-specific transcriptome profiling of the primary root pericycle 64 h after germination, thus before lateral root initiation, via a combination of laser capture microdissection and subsequent microarray analyses of 12k maize microarray chips revealed 90 genes preferentially expressed in the wild-type pericycle and 73 genes preferentially expressed in the rum1 pericycle (fold change .2; P-value ,0.01; estimated false discovery rate of 13.8%). Among the 51 annotated genes predominately expressed in the wild-type pericycle, 19 genes are involved in signal transduction, transcription, and the cell cycle. This analysis defines an array of genes that is active before lateral root initiation and will contribute to the identification of checkpoints involved in lateral root formation downstream of rum1.

Root system architecture: insights fromArabidopsisand cereal crops

“…The lrt1 [121] and rum1 [122] mutants fail to initiate lateral roots (in rum1 at least this appears to be due to disrupted auxin transport) whereas slr1 and slr2 [123] are affected after initiation, leading to reduced lateral root elongation.…”

TheGibberellic Acid Stimulated-LikeGene Family in Maize and Its Role in Lateral Root Development

“…In the wild type, weak ZmGSL2 expression is detectable in primary roots but not in seminal or crown roots. In primary roots of the lateral root mutants lrt1 (Hochholdinger and Feix, 1998) and rum1 (Woll et al, 2005), however, ZmGSL2 gene expression is abolished. Together with the fact that no corresponding ortholog can be assigned to ZmGSL2 in phylogenetic analyses, these results propose that ZmGSL2 represents a maize-specific checkpoint of lateral root formation in primary roots that is likely to depend on the activity of LRT1 and RUM1.…”

“…Therefore, as a first step in elaborating on the potential function of the ZmGSL gene family in lateral root development, ZmGSL gene expression (Fig. 2) was surveyed in primary (PR), seminal, and crown roots of the wild type by semiquantitative (sq) PCR and compared to expression in primary roots of the lateral root mutants lrt1 (PR lrt1; Hochholdinger and Feix, 1998) and rum1 (PR rum1; Woll et al, 2005). For any PCR product, amplification of the correct cDNA fragment was verified by cloning and sequencing of the corresponding amplicon.…”

“…In contrast to Arabidopsis, the molecular mechanisms underlying lateral root formation in maize are largely unknown, and genes involved have not been described so far. The analysis of lateral root mutants (Hochholdinger and Feix, 1998;Hochholdinger et al, 2001;Woll et al, 2005), however, has shed some light on the genetic control of lateral root development in maize. All mutants identified so far affect lateral root formation only in the embryonic root system, while postembryonic root development remains unaffected: In the monogenic recessive lateralrootless1 mutant (lrt1; Hochholdinger and Feix, 1998), lateral roots are not initiated at the primary root, whereas the recessive mutant rootless with undetectable meristems1 (rum1; Woll et al, 2005) fails to initiate lateral roots at the primary root and at seminal roots.…”

Branching Out in Roots: Uncovering Form, Function, and Regulation

“…A number of lateral root mutants have been described in cereals (Table II), the majority of which are auxin related (Hochholdinger and Tuberosa, 2009). For example, in maize, mutation of rootless with undetectable meristems1 (RUM1), which encodes a member of the Auxin/IAA (Aux/IAA) family of transcription factors, leads to the failure of lateral root initiation and disruptions in vascular patterning (Woll et al, 2005;von Behrens et al, 2011;Zhang et al, 2014).…”