Cell layer specific roles for hormones in root development: Gibberellins suppress infection thread progression, promote nodule and lateral root development in the endodermis and interact with auxin and cytokinin

Abstract

SummaryGibberellins have a profound influence on the formation of lateral root organs. However, the precise role this hormone plays in the cell-specific events during lateral root formation, rhizobial infection and nodule organogenesis, including interactions with auxin and cytokinin, is not clear.We performed epidermal- and endodermal-specific complementation of the severely gibberellin-deficientnapea (Pisum sativum) mutant withAgrobacterium rhizogenes. Gibberellin mutants were used to examine the spatial expression pattern of cytokinin (TCSn) and auxin (DR5) responsive promoters and hormone levels.We found that gibberellins produced in the endodermis promote lateral root and nodule organogenesis and can induce a mobile signal(s) that suppresses rhizobial infection. In contrast, epidermal-derived gibberellins suppress infection but have little influence on root or nodule development. Gibberellins suppress the cytokinin-responsiveTCSnpromoter in the cortex and are required for normal auxin activation during nodule primordia formation.Our findings indicate that gibberellins regulate the checkpoints between infection thread penetration of the cortex and invasion of nodule primordial cells and promotes the subsequent progression of nodule development. It appears that gibberellins limit the progression and branching of infection threads in the cortex by restricting cytokinin response and activate auxin response to promote nodule primordia development.