Receptor kinase LecRK-I.9 regulates cell wall remodelling and signalling during lateral root formation in Arabidopsis

Assembling and remodelling the cell wall is essential for plant development. Cell wall dynamic is controlled by cell wall proteins and a variety of sensor and receptor systems. LecRK-I.9, an Arabidopsis thaliana plasma membrane-localised lectin receptor kinase, was previously shown to be involved in cell wall-plasma membrane contacts and to play roles in plant-pathogen interactions, but so far, its role in development was unknown. LecRK-I.9 is transcribed at a high level in root tissues including the pericycle. Comparative transcript profiling of a loss-of-function mutant vs wild type identifies LecRK-I.9 as a regulator of cell wall metabolism. Consistently, lecrk-I.9 mutants display an increased pectin methylesterification level correlated with decreased pectin methylesterase and increased polygalacturonase activities. Also, LecRK-I.9 impacts lateral root development through the regulation of genes encoding (i) cell wall remodelling proteins during early events of lateral root initiation, and (ii) cell wall signalling peptides (CLE2, CLE4) repressing lateral root emergence and growth. Besides, low nitrate reduces LecRK-I.9 expression in pericycle and interferes with its regulatory network: however, the control of CLE2 and CLE4 expression is maintained. Altogether, the results show that LecRK-I.9 is a key player in a signalling network regulating both pre-branch site formation and lateral root emergence. HighlightThe lectin receptor kinase LecRK-I.9 regulates the molecular events leading to lateral root formation in both the initiation and emergence processes in Arabidopsis through cell wall remodelling enzymes and signalling peptides.