Diverse functions of GmNLA1 members in controlling phosphorus homeostasis highlight coordinate response of soybean to nitrogen and phosphorus availability

Nitrogen (N) and phosphorus (P) are two essential mineral nutrients for plant growth, which are required in relative high amount in plants. Plants have evolved a series of strategies for coordinately acquiring and utilizing N and P. However, physiological and molecular mechanisms underlying of N and P interactions remain largely unclear in soybean (Glycine max). In this study, interactions of N and P were demonstrated in soybean as reflected by significant increases of phosphate (Pi) concentration in both leaves and roots by N deficiency under Pi sufficient conditions. A total of four nitrogen limitation adaptation (NLA), encoding RING-type E3 ubiquitin ligase were subsequently identified in soybean genome. Among them, transcription of GmNLA1-1 and GmNLA1-3 was decreased in soybean by N starvation under Pi sufficient conditions, not for GmNLA1-2. Suppression of all three GmNLA1 members was able to increase Pi concentration regardless of the P and N availability in the growth medium, but decrease fresh weight under normal conditions in soybean hairy roots. However, comparted to changes in control lines at two N levels, N deficiency only resulted in a relatively higher increase of Pi concentration in GmNLA1-1 or GmNLA1-3 suppression lines, strongly indicating that GmNLA1-1 and GmNLA1-3 might regulate P homeostasis in soybean response to N starvation. Taken together, our result suggest that redundant and diverse functions present in GmNLA1 members for soybean coordinate responses to P and N availability, which mediate P homeostasis.