Crown Root Development Research Articles

Overexpression of a Transcription Factor OsMADS15 Modifies Plant Architecture and Flowering Time in Rice (Oryza sativa L.)

The MADS-box gene family encodes conserved transcription factors and functions not only in reproductive development, but also in vegetative growth. In this study, a rice MADS-box gene OsMADS15, an ortholog of Arabidopsis AP1 gene, has been functionally characterized. Rice seedlings overexpressing OsMADS15 showed precocious phenotypes of early internode elongation, shoot-borne crown root development, reduced plant height and early flowering. The axillary buds developments in OsMADS15 overexpressors were accelerated, and the buds frequently grew into effective tillers. The panicles of OsMADS15 transgenic rice plants were largely compromised for growth and branching in comparison with wild type. In the tillering stage, the OsMADS15 overexpression rice plants tillered later and less than the wild type, and in the maturity stage, the culms of the overexpression lines bore more stem nodes. Quantitative polymerase chain reaction (PCR) results showed that expression levels of WUSCHEL-related Homeobox (WOX) gene, WOX11, and some flowering regulators were promoted in the OsMADS15 overexpression transgenic plants, indicating that OsMADS15 had a wide range of regulations. These results clearly indicate that OsMADS15 plays important roles not only in transition to reproductive development, but also in crown root development.

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.

Transcript profiling of crown rootless1 mutant stem base reveals new elements associated with crown root development in rice

BackgroundIn rice, the major part of the post-embryonic root system is made of stem-derived roots named crown roots (CR). Among the few characterized rice mutants affected in root development, crown rootless1 mutant is unable to initiate crown root primordia. CROWN ROOTLESS1 (CRL1) is induced by auxin and encodes an AS2/LOB-domain transcription factor that acts upstream of the gene regulatory network controlling CR development.ResultsTo identify genes involved in CR development, we compared global gene expression profile in stem bases of crl1 mutant and wild-type (WT) plants. Our analysis revealed that 250 and 236 genes are down- and up-regulated respectively in the crl1 mutant. Auxin induces CRL1 expression and consequently it is expected that auxin also alters the expression of genes that are early regulated by CRL1. To identify genes under the early control of CRL1, we monitored the expression kinetics of a selected subset of genes, mainly chosen among those exhibiting differential expression, in crl1 and WT following exogenous auxin treatment. This analysis revealed that most of these genes, mainly related to hormone, water and nutrient, development and homeostasis, were likely not regulated directly by CRL1. We hypothesized that the differential expression for these genes observed in the crl1 mutant is likely a consequence of the absence of CR formation. Otherwise, three CRL1-dependent auxin-responsive genes: FSM (FLATENNED SHOOT MERISTEM)/FAS1 (FASCIATA1), GTE4 (GENERAL TRANSCRIPTION FACTOR GROUP E4) and MAP (MICROTUBULE-ASSOCIATED PROTEIN) were identified. FSM/FAS1 and GTE4 are known in rice and Arabidopsis to be involved in the maintenance of root meristem through chromatin remodelling and cell cycle regulation respectively.ConclusionOur data showed that the differential regulation of most genes in crl1 versus WT may be an indirect consequence of CRL1 inactivation resulting from the absence of CR in the crl1 mutant. Nevertheless some genes, FAS1/FSM, GTE4 and MAP, require CRL1 to be induced by auxin suggesting that they are likely directly regulated by CRL1. These genes have a function related to polarized cell growth, cell cycle regulation or chromatin remodelling. This suggests that these genes are controlled by CRL1 and involved in CR initiation in rice.

OsCAND1 Is Required for Crown Root Emergence in Rice

Crown roots are main components of the fibrous root system and important for crops to anchor and absorb water and nutrition. To understand the molecular mechanisms of crown root formation, we isolated a rice mutant defective in crown root emergence designated as Oscand1 (named after the Arabidopsis homologous gene AtCAND1). The defect of visible crown root in the Oscand1 mutant is the result of cessation of the G2/M cell cycle transition in the crown root meristem. Map-based cloning revealed that OsCAND1 is a homolog of Arabidopsis CAND1. During crown root primordium development, the expression of OsCAND1 is confined to the root cap after the establishment of fundamental organization. The transgenic plants harboring DR5::GUS showed that auxin signaling in crown root tip is abnormal in the mutant. Exogenous auxin application can partially rescue the defect of crown root development in Oscand1. Taken together, these data show that OsCAND1 is involved in auxin signaling to maintain the G2/M cell cycle transition in crown root meristem and, consequently, the emergence of crown root. Our findings provide new information about the molecular regulation of the emergence of crown root in rice.

Does nitric oxide play a pivotal role downstream of auxin in promoting crown root primordia initiation in monocots?

Increasing instances prove that nitric oxide (NO) plays a significant role in mediating root growth and development, and it is reported that NO acts as a messenger and mediates the auxin-induced adventitious roots (AR) developing process in cucumber explants. Compared with the current understanding of AR development in dicots, knowledge of the molecular and physiological mechanisms of crown root (CR) development in monocots is limited, and the roles of NO in CR initiation and development are still far from clear. Our recent studies demonstrate that a critical concentration of endogenous NO is indispensable for CR primordia initiation, the reduction of endogenous NO content blocks CR primordia initiation and decreases CR number in rice seedlings. In this addendum, Base on the results of our studies and previous reports, we supposed that CR formtion in monocots and AR formtion in dicots possible take part in the same NO signaling pathway, althoug in dicots, AR are formed under unusual circumstances and belong to the abnormal developmental program, and in monocot cereals, CR are genetically determined roots and belong to the normal developmental program of cereals. At last, we advanced a proposed schematic model showing the NO signaling pathway of CR emergence in monocots.

The WUSCHEL-Related Homeobox GeneWOX11Is Required to Activate Shoot-Borne Crown Root Development in Rice

In rice (Oryza sativa), the shoot-borne crown roots are the major root type and are initiated at lower stem nodes as part of normal plant development. However, the regulatory mechanism of crown root development is poorly understood. In this work, we show that a WUSCHEL-related Homeobox (WOX) gene, WOX11, is involved in the activation of crown root emergence and growth. WOX11 was found to be expressed in emerging crown roots and later in cell division regions of the root meristem. The expression could be induced by exogenous auxin or cytokinin. Loss-of-function mutation or downregulation of the gene reduced the number and the growth rate of crown roots, whereas overexpression of the gene induced precocious crown root growth and dramatically increased the root biomass by producing crown roots at the upper stem nodes and the base of florets. The expressions of auxin- and cytokinin-responsive genes were affected in WOX11 overexpression and RNA interference transgenic plants. Further analysis showed that WOX11 directly repressed RR2, a type-A cytokinin-responsive regulator gene that was found to be expressed in crown root primordia. The results suggest that WOX11 may be an integrator of auxin and cytokinin signaling that feeds into RR2 to regulate cell proliferation during crown root development.

Release of the benzoxazinoids defense molecules during lateral- and crown root emergence in Zea mays

We observed the release of the benzoxazinoids defense molecules on the surface of the primary root and the coleoptilar node in Zea mays during the emergence of lateral- and crown-roots, respectively. At later stages of crown root and lateral root development, benzoxazinoids around the emerged roots were no longer observed. Specific mutants revealed that the developmental status of the emerged roots was not important for the release of benzoxazinoids, but the breakage of the epidermis by emerging roots was. This is the first report of benzoxazinoid-release during normal development controlled by endogenous developmental programs. Release of benzoxazinoids around the emerging roots supports the idea that defense molecules accumulate at the site of root emergence in order to reduce pathogenic infections. We discuss possible explanations for the evolution of two different developmental mechanisms of root emergence.

Histological reconstruction of dental development and age at death of a juvenile Paranthropus robustus specimen, SK 63, from Swartkrans, South Africa

There has been disagreement about whether the earliest hominids grew in a similar manner to great apes or modern humans. This has important biological implications, since it may have been inappropriate to apply modern human developmental standards to early hominids. The aim of the present study was to combine data from replicas of tooth surfaces, computed tomographic (CT) scans, and radiographs with data from a histological section of the canine crown, in order to provide a complete description of tooth crown and tooth root development in a single early hominid specimen (SK 63). Although partially destructive in nature, we have been able to determine the most reliable data yet for aspects of dental development in an important juvenile early hominid specimen. Appositional enamel formation time in the permanent right canine was estimated at between 305 and 418 days, imbricational enamel formation time at 819 days, and total crown formation time at between 3.18 and 3.48 years. The most likely age at death was estimated at around 4 years with a range of ages calculated between 3.18 and 4.23 years based on differences in timing of initial mineralization of the canine and differences in appositional enamel formation times. Crown formation times of the lower central and lateral incisors were estimated between 2.35-2.68 years and 2.57-2.91 years, respectively. Crown formation time of the first permanent molar was estimated at 2.4 years. Wear facets on the first permanent molars indicate that gingival emergence had occurred sometime prior to death, between 3 and 4 years of age. Estimates of root extension rates in the first permanent molars and in the permanent incisors are fast, and either within or above ranges of rates estimated for modern great apes. While we recognize that data for one individual may not be representative of data for a whole population of early hominids, the data for age at death, for age of M1 emergence, and for root extension rates presented here accord with those known for modern great apes and fall beyond the known ranges for modern humans.

1987 Kreshover lecture. Gene regulation in the development of oral tissues.

The regulatory processes associated with tooth formation are being investigated by the identification of when, where, and how cell adhesion molecules (CAMs), substrate adhesion molecules (SAMs), dentin phosphoprotein, enamel gene products, and intermediate cementum products are expressed during sequential developmental stages of morphogenesis, cytodifferentiation, dentin, enamel and cementum extracellular matrix (ECM) formation, and biomineralization. Instructive and permissive signaling is required for both morphogenesis and cytodifferentiation based upon in vitro organotypic culture studies in serumless, chemically-defined medium. Intrinsic developmental instructions, independent of exogenous growth factors, mediate tooth morphogenesis from the initiation of the dental lamina through crown and initial root development. Recent progress using recombinant DNA methods has advanced descriptions of several dental structural genes. The complete nucleic acid sequence for mouse amelogenin has been defined. This sequence is located on the mouse X chromosome and on the human X and Y chromosomes. This discussion summarizes recent results using experimental embryology, recombinant DNA technology, and immunocytology in the context of instructive epithelial-mesenchymal interactions associated with epithelial differentiation into ameloblasts, ectomesenchyme differentiation into odontoblasts, and dentin and enamel ECM biomineralization. The tooth organ provides opportunities at several levels of biological organization to investigate cellular, molecular, and developmental processes.

On the "leaf-cutting" method for the observation of crown root development in rice plants

On the "leaf-cutting" method for the observation of crown root development in rice plants

Some Observations on the Root Development in Rice Plant with Respect to Its Concurrency with Leaf Emergence and Internode Elongation

Growth of the above-and under-ground parts of rice plant was observed to clarify their developmental phase coincidence. 1. The concurrence among the leaf emergence, the internode elongation, and the ascent of node-locus where the emergence of new roots were prevailing in the main stem is presumed as follows: At the time of emergence of the N-th leaf (denote the node number from which the N-th leaf emerged as n), the (n-2)∼(n-3)-th internodes attained their full lengths, and crown root emergence was prevailing on the (n-3)-th node. 2. But, at the conversion stage of leaf emergence, the ascending pace of root emarging locus and the rate of root number increase were checked, and at the stage of uppermost leaf emergence, crown root development was observed on the (n-4)-th node. 3. The total area of the cross section of secondary xylems per single root measured larger as the root emerging node-locus ascended higher, up to the conversion stage of leaf emergence, and it diminished, thereafter. 4. The secondary thickening of the metaxylem was not observed in the root of any locus.