Abstract
Leguminous plant roots can form a symbiosis with soil-dwelling nitrogen-fixing rhizobia, leading to the formation of a new root organ, the nodule. Successful nodulation requires co-ordination of spatially separated events in the root, including infection in the root epidermis and nodule organogenesis deep in the root cortex. We show that the hormone gibberellin plays distinct roles in these epidermal and cortical programmes. We employed a unique set of genetic material in pea that includes severely gibberellin-deficient lines and della-deficient lines that enabled us to characterize all stages of infection and nodule development. We confirmed that gibberellin suppresses infection thread formation and show that it also promotes nodule organogenesis into nitrogen-fixing organs. In both cases, this is achieved through the action of DELLA proteins. This study therefore provides a mechanism to explain how both low and high gibberellin signalling can result in reduced nodule number and reveals a clear role for gibberellin in the maturation of nodules into nitrogen-fixing organs. We also demonstrate that gibberellin acts independently of ethylene in promoting nodule development.
Highlights
Nodulation is the interaction between compatible legumes and rhizobial bacteria that involves the uptake of these soil bacteria into newly formed root organs termed nodules.The plant strictly controls the extent of nodulation, by various means such as acting through plant hormones including the gibberellins (GAs) (Ferguson and Mathesius, 2014; Foo, 2017)
It is essential that we reconcile the fact that both high and low GA signalling can result in suppression of the ultimate number of nodules formed in pea (Ferguson et al, 2005, 2011).To pinpoint the influence of GA on the different stages of nodulation, we employed the range of GA mutants available in pea and examined infection using lacZlabelled R. leguminosarum bv. viciae
We found a dramatic increase in the number of infection threads formed in na mutants compared with the wild type on a per cell basis (Fig. 1A, P
Summary
Nodulation is the interaction between compatible legumes and rhizobial bacteria that involves the uptake of these soil bacteria into newly formed root organs termed nodules.The plant strictly controls the extent of nodulation, by various means such as acting through plant hormones including the gibberellins (GAs) (Ferguson and Mathesius, 2014; Foo, 2017). Studies with a range of GA biosynthesis mutants in pea, na (nana), ls, and lh, revealed that low GA signalling can suppress nodule formation (Ferguson et al, 2005).The small number of nodules that do form on severely GA-deficient na mutants are small and white, with reduced meristem size (Ferguson et al, 2005, 2011), suggesting that GA may be required to promote nodule organogenesis. Della mutants in pea (la cry-s; Weston et al, 2008) that display constitutive GA responses have a reduced number of nodules compared with wild-type plants (Ferguson et al, 2011), suggesting a complex role for GA signalling as both a promoter
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
