RSL class I genes positively regulate root hair development in Oryza sativa

Abstract

SummaryRoot hairs are filamentous protuberances from superficial cells of plant roots that are critical for nutrient uptake. Genes encoding ROOT HAIR DEFECTIVE-SIX LIKE (RSL) class I basic helix-loop-helix proteins are expressed in future root hair cells (trichoblasts) of the Arabidopsis thaliana root where they positively regulate root hair cell development.We characterized the function of class I genes in Oryza sativa root development. We show that there are three RSL class I genes in O. sativa and that each is expressed in developing root hair cells. Reduction of RSL class I function results in the development of shorter root hairs than in wild-type. Ectopic overexpression results in the development of ectopic root hair cells.These data suggest that expression of individual RSL class I proteins is sufficient for root hair development in the cereal O. sativa (rice). Therefore RSL class I genes have been conserved since O. sativa and A. thaliana last shared a common ancestor. However, given that RSL class I genes are not sufficient for root hair development in A. thaliana, it suggests that there are differences in the mechanisms repressing RSL class I gene activity between members of the Poaceae and Brassicaceae.

Complexity and specificity of the maize (Zea mays L.) root hair transcriptome

“…Moreover, the maize genes rsl1 (AC216731.3_FG001) and rsl2 (GRMZM2G066057) which are homologous to the Arabidopsis RHD6 and RSL1 genes have been included in the heatmap. These Arabidopsis genes and their homologs in the monocot species rice (Kim et al , 2017) and Brachypodium (Kim and Dolan, 2016) function in root hair initiation. While maize rsl1 (AC216731.3_FG001) shows the strongest expression in the meristematic zone, the elongation zone, and in root hairs, the expression of rsl2 (GRMZM2G066057) peaks in the elongation zone and shows only very low expression in other tissues (Fig.…”

“…Thus RHD6 was preferentially expressed in root hair cells (Lan et al , 2013). Double knockdown mutants of two of the three homologs of Arabidopsis, RHD6 and RSL1 , results in reduced root hair length in Brachypodium (Kim and Dolan, 2016) and rice (Kim et al , 2017), suggesting partial functional redundancy. In fact, the expression of maize homologs of Arabidopsis RHD6 and RSL1 designated rsl1 and rsl2 peaks in the elongation zone (Fig.…”

“…Homologs of those genes have been shown to control root hair development in several other species including Physcomitrella patens (Jang et al , 2011), Brachypodium distachyon (Kim and Dolan, 2016), rice (Kim et al , 2017), and Marchantia polymorpha (Proust et al , 2016). Further genes encoding bHLH transcription factors including rsl2 , rsl3 , rsl4 , and ljrhl1-like 3 ( lrl3 ) are direct targets of RHD6 and RSL1 driving the development of root hairs (Yi et al , 2010; Bruex et al , 2012).…”

Do longer root hairs improve phosphorus uptake? Testing the hypothesis with transgenic Brachypodium distachyon lines overexpressing endogenous RSL genes

“…There are three class I genes in Brachypodium , BdRSL1 , BdRSL2 or BdRSL3 , and ectopic expression of any of these genes in Brachypodium increases root hair length and density (Kim & Dolan, ). Increasing the expression of related RSL genes in rice, Arabidopsis and wheat also increased root hair length (Han et al ., ; Kim & Dolan, ; Kim et al ., ). The present study used transgenic Brachypodium differing in root hair length to test the hypothesis that longer root hairs improve P nutrition in P‐deficient soil.…”

Neofunctionalisation of basic helix−loop−helix proteins occurred when embryophytes colonised the land

“…Orthologues positively regulate the development of rhizoids and mucilage papillae in the moss Physcomitrella patens (Menand et al ., ; Jang et al ., ; Proust et al ., ). Class 1 RSL genes positively regulate the development of root hairs in diverse groups of angiosperms including Arabidopsis thaliana (Masucci & Schiefelbein, ; Menand et al ., ) and the grasses Oryza sativa and Brachypodium distachyon (Kim & Dolan, ; Kim et al ., ). Expression of RSL class 1 genes from one taxon of land plant can compensate for the loss of function in another taxon (Menand et al ., ; Kim & Dolan, ; Proust et al ., ; Kim et al ., ); expression of the M. polymorpha Mp RSL1 gene using the cauliflower mosaic virus 35S promoter (35S) in the root hairless At root hair defective 6 At root hair defective six‐like 1 (At rhd6 At rsl1 ) double mutants of A. thaliana restored root hair development (Proust et al ., ).…”