The White Lupin Trehalase Gene LaTRE1 Regulates Cluster Root Formation and Function Under Phosphorus Deficiency

Under phosphorus (P) deficiency, white lupin (Lupinus albus L.) forms a specialized root structure, called cluster root (CR), to improve soil exploration and nutrient acquisition. Sugar signaling is thought to play a vital role in the development of CR. Trehalose and its associated metabolites are the essential sugar signal molecules that link growth and development to carbon metabolism in plants; however, their roles in the control of CR are still unclear. Here, we investigated the function of the trehalose metabolism pathway by pharmacological and genetic manipulation of the activity of trehalase in white lupin, the only enzyme that degrades trehalose into glucose. Under P deficiency, validamycin A treatment, which inhibits trehalase, led to the accumulation of trehalose and promoted the formation of CR with enhanced organic acid production, whereas overexpression of the white lupin TREHALASE1 (LaTRE1) led to decreased trehalose levels, lateral rootlet density, and organic acid production. Transcriptomic and virus-induced gene silencing results revealed that LaTRE1 negatively regulates the formation of CRs, at least partially, by the suppression of LaLBD16, whose putative ortholog in Arabidopsis (Arabidopsis thaliana) acts downstream of ARF7- and ARF19-dependent auxin signaling in lateral root formation. Overall, our findings provide an association between the trehalose metabolism gene LaTRE1 and CR formation and function with respect to organic acid production in white lupin under P deficiency.