Characterization of LRL5 as a key regulator of root hair growth in maize.

Summary: Root hair, a special type of tubular‐shaped cell, outgrows from the root epidermal cell and plays important roles in the acquisition of nutrients and water, as well as interactions with biotic and abiotic stresses. Studies in the model plant Arabidopsis have revealed that root‐hair initiation and elongation are hierarchically regulated by a group of basic helix−loop−helix (bHLH) transcription factors (TFs). However, knowledge regarding the regulatory pathways of these bHLH TFs in controlling root hair growth remains limited. In this study, RNA‐seq analysis was conducted to profile the transcriptome in the elongating maize root hair and >1000 genes with preferential expression in root hair were identified. A consensus cis‐element previously featured as the potential bHLH‐TF binding sites was present in the regulatory regions for the majority of the root hair‐preferentially expressed genes. In addition, an individual change in ZmLRL5, the highest‐expressed bHLH‐TF in maize root hair resulted in a dramatic reduction in the elongation of root hair, and rendered the growth of root hair hypersensitive to translational inhibition. Moreover, RNA‐seq, yeast‐one‐hybrid and ribosome profile analysis suggested that ZmLRL5 may function as a key player in orchestrating the translational process by directly regulating the expression of translational processes/ribosomal genes during maize root hair growth. Significance statement: This work describes the identification of genes preferentially expressed in the growing maize root hair. We demonstrate a basic helix−loop−helix transcription factor, Lj‐RHL1‐LIKE 5 (ZmLRL5), that promotes root hair elongation by transcriptionally regulating the expression of genes required for translational processes and continuous protein synthesis. These results pinpoint a prospective mechanism for ZmLRL5 in functioning as a key hub in orchestrating protein synthesis by transcriptional control of translation‐related genes during root hair growth. [ABSTRACT FROM AUTHOR]