GATA23-Dependent Specification of Founder Cell in Lateral Root Initiation is not Unique for Brassicaceae

The gene regulatory network involved in lateral root (LR) initiation is well known for Arabidopsis. Transcription factor GATA23 is one of the earliest known markers up-regulated by auxin during LR development. Previous studies have shown that GATA23 is specific for Brassicaceae. Nevertheless, a search for functional orthologues of Arabidopsis GATA23 was performed in cucumber (Cucumis sativus) and squash (Cucurbita pepo) where LR initiation and development take place within the parental root meristem.

Comparative phylogenetic analysis allowed the identification of 26 genes from the GATA family of transcription factors in cucumber and squash. Based on the results of a comparative phylogenetic analyses of the DNA-binding domain of GATA proteins, cucurbit GATA genes were divided into four classes. In order to identify cucurbit GATA genes up-regulated by auxin, four-day old cucumber and squash seedlings were treated with 10 μM of naphthalene acetic acid (NAA) for 6 h, followed by qRT-PCR analysis of GATA gene transcription. Expression levels of the majority cucurbits GATA genes were not affected by auxin treatment. Both in cucumber and squash, expression levels of three GATA genes were very low based on qRT-PCR analysis. Only two GATA genes were found to be up-regulated in response to NAA in cucumber and one in squash. Thus, putative cucurbit orthologues of Arabidopsis GATA23 were identified based on bioinformatics and molecular methods. Tissue-specific promoter activity was analyzed using NeonGreen-H2B or tdTomato-H2B reporter fusion constructs in transgenic hairy roots and laser scanning confocal microscopy. Analyses of the role of these putative orthologues in LR initiation are in progress using chimeric repressor gene-silencing technology.

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