A Novel ABA Insensitive Mutant of Lotus japonicus with a Wilty Phenotype Displays Unaltered Nodulation Regulation

Abstract

An ABA insensitive mutant, Beyma, was isolated in Lotus japonicus MG-20 from an EMS mutagenesis population using root growth inhibition to applied ABA as the screening criterion. (The name 'Beyma' was taken from the Australian Aboriginal language, Wagiman, beyma, meaning 'drying up'.) The stable mutant that segregates as a dominant Mendelian mutation is insensitive to ABA induced inhibition of germination, vegetative growth, stomatal opening, as well as nodulation. Tissue ABA levels were normal, suggesting a sensitivity rather than biosynthesis mutation. It is slow-growing (50-70% of wild-type MG-20) and has a near-constitutive wilty phenotype associated with its inability to regulate stomatal opening. Whilst showing a wide range of ABA insensitive phenotypes, Beyma did not show alteration of nodule number control, as, in the absence of added ABA, the number and patterning (but not size) of nodules formed in the mutant were similar to that of MG-20. Split root experiments on MG-20 showed that application of ABA on one side of the root inhibited nodulation locally but not systemically. We propose that ABA is not involved directly in systemic autoregulation of nodulation (AON).

Control of root architecture and nodulation by theLATD/NIPtransporter

“…35 Evidence for a separate branch of the ABA signaling pathway that does not regulate nodulation comes from the L. japonicus beyma mutant, which is ABA-insensitive for several classic ABAresponsive phenotypes, but has no effect on nodule number. 38 Together, analysis of these mutants suggests a complex role for ABA in coordinating multiple aspects of nodule development. Characterization of additional legume mutants will extend our understanding of the ABA signaling pathway and the way in which it intersects with nodulation.…”

“…Also, there is no evidence that either LATD/NIP specifically or ABA signaling in general is involved in AON. 2,38 If LATD/NIP is a transporter, more likely candidates for transport are nitrate and ABA (Fig. 2).…”

Specific Subunits of Heterotrimeric G Proteins Play Important Roles during Nodulation in Soybean

“…Abscisic acid (ABA) was chosen as an additional signal for these experiments because it is an established regulator of Gprotein signaling in plants (Pandey et al, 2006. Furthermore, ABA also affects nodule formation, although some conflicting information exists on its role in different species Biswas et al, 2009). Treatment of EV control and different RNAi lines with 5 mM ABA following B. japonicum infection led to a significant decrease in the number of nodules formed in soybean roots.…”

Plant Hormonal Regulation of Nitrogen-Fixing Nodule Organogenesis

“…Ethylene, a major local inhibitory signal in symbiosis Legumes have evolved local inhibitory regulation systems of nodulation via hormones such as Abscisic acid (ABA), Jasmonic acid (JA), ethylene, and SA (Salicylic acid), in addition to systemic AON signaling (Biswas et al, 2009;Ding et al, 2008;Oldroyd et al, 2001;Penmetsa and Cook, 1997;Sun et al, 2006;Suzuki et al, 2004) (Fig. 2B).…”