Lateral Root Initiation in the Primary Root Meristem of Cucurbits: Old Players in a New Position - ISRR 2018 10th Symposium for the International Society of Root Research

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¹Laboratory of Cellular and Molecular Mechanisms of Plant Development, Komarov Botanical Institute of the Russian Academy of Sciences, Russia
²Laboratory of Molecular and Cellular Biology, All-Russia Research Institute for Agricultural Microbiology, Russia
³Department of Ecology, Environment and Plant Sciences, Stockholm University, Sweden

In some flowering plant families including Cucurbitaceae initiation and development of lateral roots (LR) take place not in the differentiation zone, but directly in the apical meristem of the parental root. Our study aims to identify the general molecular genetic mechanisms leading to LR initiation (LRI) in flowering plants. We know the key players involved in the specification of the LR founder cells and the transition to formative divisions during Arabidopsis LRI. Rapid alkalinization factor (RALF34) has been suggested to be the earliest marker for specification of LR founder cell identity. The auxin-regulatory transcription factor GATA23 can be seen as the next player in the maintenance of lateral root founder cells. Expression of membrane-associated kinase regulator 4 (MAKR4) is required for the first anticlinal divisions in the pericycle which leads to the conversion of prebranch sites into lateral root primordia. Recently we have shown that the auxin signaling plays a central role in the specification of the LR founder cells not only in Arabidopsis but also in Cucurbitaceae. Local auxin response maxima in individual pericycle cells, and in case of Cucurbitaceae, also in the endodermis, are associated with the identification of founder cells and precede the first formative anticlinal divisions.

In order to analyse the gene network involved in LRI in cucumber (Cucumis sativus) and squash (Cucurbita pepo), putative orthologues of Arabidopsis RALF34, GATA23 and MAKR4 were identified. The pattern of cell- and tissue-specific promoter activity was analysed using NeonGreen-H2B or tdTomato-H2B reporter gene fusion constructs in transgenic hairy roots by laser scanning confocal microscopy and 3D imaging. Literature data, as well as results obtained in this study, suggest that flowering plants, independent of their position of LRI, use a common gene network for this purpose which is regulated by auxin.

This work was supported by Russian Science Foundation (16-16-00089).