Role In Lateral Root Development Research Articles

MiRNA164-directed cleavage of ZmNAC1 confers lateral root development in maize (Zea maysL.)

BackgroundMicroRNAs are a class of small, non-coding RNAs that regulate gene expression by binding target mRNA, which leads to cleavage or translational inhibition. The NAC proteins, which include NAM, ATAF, and CUC, are a plant-specific transcription factor family with diverse roles in development and stress regulation. It has been reported that miR164 negatively regulates NAC1 expression, which in turn affects lateral root development in Arabidopsis; however, little is known about the involvement of the maize NAC family and miR164 in lateral root development.ResultsWe collected 175 maize transcripts with NAC domains. Of these, 7 ZmNACs were putative targets for regulation by miR164. We isolated one gene, called TC258020 (designated ZmNAC1) from 2 maize inbred lines, 87-1 and Zong3. ZmNAC1 had a high expression level in roots and showed higher abundance (1.8 fold) in Zong3 relative to 87-1, which had less lateral roots than Zong3. There was a significant correlation between the expression level of ZmNAC1 and the lateral root density in the recombinant inbred line (RIL) population. Transgenic Arabidopsis that overexpressed ZmNAC1 had increased lateral roots in comparison to the wild type. These findings suggest that ZmNAC1 played a significant role in lateral root development. An allelic expression assay showed that trans-regulatory elements were the dominant mediators of ZmNAC1 differential expression in 87-1 and Zong3, and further analysis revealed that miR164 was a trans-element that guided the cleavage of endogenous ZmNAC1 mRNA. Both mature miR164 and miR164 precursors had higher expression in 87-1 than Zong3, which was the opposite of the expression pattern of ZmNAC1. Additionally, the allelic assay showed that the cis-regulatory element most likely affected Zm-miR164b's expression pattern. A β-glucuronidase (GUS) assay showed that the Zm-miR164b promoter had higher GUS activity in 87-1 than in Zong3. In addition, we detected miR164b expression in the RIL population, and the results indicated that miR164b had a higher expression level in the RILs containing 87-1 promoter than those containing Zong3 promoter.ConclusionOur results indicate one possible pathway in maize by which differences in miR164b promoter activity resulted in a different expression pattern for mature miR164 which negatively regulates ZmNAC1 expression in 87-1 and Zong3, thereby contributing to a significantly different lateral root phenotype.

A Gain-of-Function Mutation in OsIAA11 Affects Lateral Root Development in Rice

Lateral roots are important to plants for the uptake of nutrients and water. Several members of the Aux/IAA family have been shown to play crucial roles in lateral root development. Here, a member of the rice Aux/IAA family genes, OsIAA11 (LOC_Os03g43400), was isolated from a rice mutant defective in lateral root development. The gain-of-function mutation in OsIAA11 strictly blocks the initiation of lateral root primordia, but it does not affect crown root development. The expression of OsIAA11 is defined in root tips, lateral root caps, steles, and lateral root primordia. The auxin reporter DR5-GUS (β-glucuronidase) was expressed at lower levels in the mutant than in wild-type, indicating that OsIAA11 is involved in auxin signaling in root caps. The transcript abundance of both OsPIN1b and OsPIN10a was diminished in root tips of the Osiaa11 mutant. Taken together, the results indicate that the gain-of-function mutation in OsIAA11 caused the inhibition of lateral root development in rice.

Hormonal Regulation of Lateral Root Development in Arabidopsis Modulated byMIZ1and Requirement of GNOM Activity forMIZ1Function

Plant organ development is important for adaptation to a changing environment. Genetic and physiological studies have revealed that plant hormones play key roles in lateral root formation. In this study, we show that MIZU-KUSSEI1 (MIZ1), which was identified originally as a regulator of hydrotropism, functions as a novel regulator of hormonally mediated lateral root development. Overexpression of MIZ1 (MIZ1OE) in roots resulted in a reduced number of lateral roots being formed; however, this defect could be recovered with the application of auxin. Indole-3-acetic acid quantification analyses showed that free indole-3-acetic acid levels decreased in MIZ1OE roots, which indicates that alteration of auxin level is critical for the inhibition of lateral root formation in MIZ1OE plants. In addition, MIZ1 negatively regulates cytokinin sensitivity on root development. Application of cytokinin strongly induced the localization of MIZ1-green fluorescent protein to lateral root primordia, which suggests that the inhibition of lateral root development by MIZ1 occurs downstream of cytokinin signaling. Surprisingly, miz2, a weak allele of gnom, suppressed developmental defects in MIZ1OE plants. Taken together, these results suggest that MIZ1 plays a role in lateral root development by maintaining auxin levels and that its function requires GNOM activity. These data provide a molecular framework for auxin-dependent organ development in Arabidopsis (Arabidopsis thaliana).

Multimodular auxin response controls lateral root development in Arabidopsis

In plants, the phytohormone auxin plays a prominent role in controlling nearly every step in plant growth and development. However, it is unclear how one generic signal such as auxin can be translated in so many diverse developmental responses. Recently, we could show that, next to its well known role in embryogenesis, the auxin response module controlled by the BODENLOS (BDL)/INDOLE-3-ACETIC ACID12 (IAA12)-MONOPTEROS (MP)/AUXIN RESPONSE FACTOR5 (ARF5) pair also plays a role in lateral root development, and that this auxin response succeeds the one controlled by SOLITARY ROOT (SLR)/IAA14-ARF7-ARF19. We conclude that bi- or multimodular response mechanisms might be a general principle of auxin signaling in plants, which provides a genetic framework for a single molecule such as auxin to have many diverse functions.

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

In an approach to study lateral root development in monocots, genome-wide searches for homologs of the Gibberellic Acid Stimulated Transcript-like (GAST-like) gene family in rice (Oryza sativa) and maize (Zea mays) were carried out. Six novel GAST-like genes in rice and 10 members of the gene family in maize, which were designated ZmGSL (for Z. mays Gibberellic Acid Stimulated-Like), were identified. The ZmGSL family encodes small proteins of 75 to 128 amino acids, which are characterized by a conserved 59 to 64 amino acid C-terminal domain. Within this domain, 17 amino acids, including 12 cysteines, are perfectly conserved. The transcript of the ZmGSL1 gene is differentially spliced into the alternative variants ZmGSL1a and ZmGSL1b, the latter of which is translated into a premature protein that lacks the C-terminal domain. The presence of an additional N-terminal cleavable signal sequence in eight of the 10 ZmGSL proteins suggests that they are secreted into the extracellular matrix. In-depth root-specific gene expression analyses carried out in the wild type and the lateral root mutants lrt1 and rum1 suggest a role for ZmGSL genes in early lateral root development, which is likely regulated by gibberellic acid. Expression patterns of ZmGSL1a and ZmGSL1b propose antagonistic functions of these splice variants during early lateral root formation.