Molecular Evolution of Auxin-Mediated Root Initiation in Plants

The root originated independently in euphyllophytes (ferns and seed plants) and lycophytes; however, the molecular evolutionary route of root initiation remains elusive. By analyses of the fern Ceratopteris richardii and seed plants, here we show that the molecular pathway involving auxin, intermediate-clade WUSCHEL-RELATED HOMEOBOX (IC-WOX) genes, and WUSCHEL-clade WOX (WC-WOX) genes could be conserved in root initiation. We propose that the "auxin>IC-WOX>WC-WOX" module in root initiation might have arisen in the common ancestor of euphyllophytes during the second origin of roots, and that this module has further developed during the evolution of different root types in ferns and seed plants.

Regulation of Sixth Seminal Root Formation by Jasmonate in Triticum aestivum L

A well-developed root system is an important characteristic of crop plants, which largely determines their productivity, especially under conditions of water and nutrients deficiency. Being Poaceous, wheat has more than one seminal root. The number of grown seminal roots varies in different wheat accessions and is regulated by environmental factors. Currently, the molecular mechanisms determining the number of germinated seminal roots remain poorly understood. The analysis of the root system development in germinating seeds of genetically modified hexaploid wheat plants with altered activity of jasmonate biosynthesis pathway and seeds exogenously treated with methyl jasmonate revealed the role of jasmonates in the regulation of sixth seminal root development. This regulatory effect strongly depends on the jasmonate concentration and the duration of the exposure to this hormone. The maximum stimulatory effect of exogenously applied methyl jasmonate on the formation of the sixth seminal root was achieved at 200 μM concentration after 48 h of treatment. Further increase in concentration and exposure time does not increase the stimulating effect. While 95% of non-transgenic plants under non-stress conditions possess five or fewer seminal roots, the number of plants with developed sixth seminal root reaches up to 100% when selected transgenic lines are treated with methyl jasmonate.

Abscisic Acid Regulates Auxin Distribution to Mediate Maize Lateral Root Development Under Salt Stress

Roots are important plant organs. Lateral root (LR) initiation (LRI) and development play a central role in environmental adaptation. The mechanism of LR development has been well investigated in Arabidopsis. When we evaluated the distribution of auxin and abscisic acid (ABA) in maize, we found that the mechanism differed from that in Arabidopsis. The distribution of ABA and auxin within the primary roots (PRs) and LRs was independent of each other. Auxin localization was observed below the quiescent center of the root tips, while ABA localized at the top of the quiescent center. Furthermore, NaCl inhibited LRI by increasing ABA accumulation, which mainly regulates auxin distribution, while auxin biosynthesis was inhibited by ABA in Arabidopsis. The polar localization of ZmPIN1 in maize was disrupted by NaCl and exogenous ABA. An inhibitor of ABA biosynthesis, fluridone (FLU), and the ABA biosynthesis mutant vp14 rescued the phenotype under NaCl treatment. Together, all the evidence suggested that NaCl promoted ABA accumulation in LRs and that ABA altered the polar localization of ZmPIN1, disrupted the distribution of auxin and inhibited LRI and development.

Overexpression of wheat gene TaMOR improves root system architecture and grain yield in Oryza sativa

Improved root architecture is an effective strategy to increase crop yield. We demonstrate that overexpression of transcription factor gene MORE ROOT (TaMOR) from wheat (Triticum aestivum L.) results in more roots and higher grain yield in rice (Oryza sativa). TaMOR, encoding a plant-specific transcription factor belonging to the ASYMMETRIC LEAVES2/LATERAL ORGAN BOUNDARIES (AS2/LOB) protein family, is highly conserved in wheat and its wild relatives. In this study, tissue expression patterns indicated that TaMOR mainly localizes to root initiation sites. The consistent gene expression pattern suggests that TaMOR is involved in root initiation. Exogenous auxin treatment induced TaMOR expression without de novo protein biosynthesis. Both in vivo and in vitro experiments demonstrated that TaMOR interacts with TaMOR-related protein TaMRRP, which contains a four-tandem-pentatricopeptide repeat motif. Overexpression of TaMOR led to more lateral roots in Arabidopsis thaliana, and TaMOR-overexpressing rice plants had more crown roots, a longer main panicle, a higher number of primary branches on the main panicle, a higher grain number per plant, and higher yield per plant than the plants of wild type. In general, TaMOR-D-overexpressing lines had larger root systems in Arabidopsis and rice, and produce a higher grain yield per plant. TaMOR therefore offers an opportunity to improve root architecture and increase yield in crop plants.