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The number of root cortex cell layers varies among plants, and many species have several cortical cell layers. We recently demonstrated that the two rice orthologs of the Arabidopsis SHR gene, OsSHR1 and OsSHR2, could complement the A. thaliana shr mutant. Moreover, OsSHR1 and OsSHR2 expression in A. thaliana roots induced the formation of extra root cortical cell layers. In this article, we demonstrate that the overexpression of AtSHR and OsSHR2 in rice roots leads to plants with wide and short roots that contain a high number of extra cortical cell layers. We hypothesize that SHR genes share a conserved function in the control of cortical cell layer division and the number of ground tissue cell layers in land plants., (Copyright © 2017 Elsevier Inc. All rights reserved.)

In plants, MADS-box transcription factors are key regulators of floral and fruit development, organ dehiscence and stress responses. Nevertheless, the functions of most of them are still unknown. In Arabidopsis thaliana, the AGL17-like clade of MADS-box transcription factors comprises four members. AGL17 is involved in floral induction, whereas AGL44/ANR1 is involved in the adaptive development of roots in response to nitrate. AGL21 is primarily expressed in the roots and AGL16 in the leaves, suggesting that these transcription factors may be involved in the control of vegetative development. In Oryza sativa, the AGL17-like clade comprises five members, OsMADS23, OsMADS25, OsMADS27, OsMADS57 and OsMADS61. In a first attempt to characterize their functions, we used promoter::Gus reporter gene fusions and RT-qPCR to study the expression patterns of these genes and their regulation by different external stimuli. The OsMADS23, OsMADS25, OsMADS27 and OsMADS57 promoters were active in the root's central cylinder. In addition, the OsMADS57 promoter was active in leaves, whereas the OsMADS61 promoter was only active in the leaf tips and the stem base. OsMADS25 and OsMADS27 transcripts accumulated in response to osmotic stress, whereas the expression levels of OsMADS25, OsMADS27 and OsMADS57 were slightly induced by nitrate. Each of these five genes was responsive to various hormonal treatments. These distinct expression patterns indicate that these five genes have specific and non-redundant functions that likely differs from those of their A. thaliana homologs., (Copyright © 2013 Elsevier B.V. All rights reserved.)

Organization of tissues in Arabidopsis thaliana root is made of, from outside in, epidermis, cortex, middle cortex, endodermis, pericycle and vascular tissues. Cortex, middle cortex and endodermis form the ground tissue (GT) system. Functional and molecular characterization of GT patterning mutants' properties has greatly increased our understanding of fundamental processes of plant root development. These studies have demonstrated GT is an elegant model that can be used to study how different cell types and cell fates are specified. This review analyzes GT mutants to provide a detailed account of the molecular network that regulates GT formation in A. thaliana. The most recent results indicate an unexpectedly complex network of transcription factors, epigenetic and hormonal controls that play crucial roles in GT development. Major differences exist between GT formation in dicots and monocots, particularly in the model plant rice, opening the way for evo-devo of GT formation in angiosperm. In rice, adaptation to submergence relies on a multilayered cortex. Moreover, variation in the number of cortex cell layers is also observed between the five root types. A mechanism of control for cortical cell number should then exist in rice and it remains to be determined if any of the Arabidopsis thaliana identified GT network members are also involved in this process in rice. Alternatively, a totally different network may have been invented. However, first available results suggest functional conservation in rice of at least two transcription factors, SHORT ROOT (SHR) and SCARECROW (SCR), involved in ground tissue formation in Arabidopsis., (Copyright © 2012 Elsevier Inc. All rights reserved.)