Phosphorus uptake is associated with the rhizosheath formation of mature cluster roots in white lupin under soil drying and phosphorus deficiency

Abstract

Phosphorus (P) deficiency largely restricts plant growth and lead to severe yield losses. Therefore, identification of novel root traits to improve P uptake is needed to circumvent yield losses. White lupin (Lupinus albus) is a legume crop that develops cluster roots and has the high phosphorus use efficiency in low P soils. We aimed to investigate the association between cluster roots (CR) rhizosheath formation and P uptake in white lupin. Rhizosheath formation and P concentration were evaluated under four soil treatments. CR increased up to 2.5-fold of overall plant dry weight under SD-P compared to WW + P (control), partly attributable to variations in CR development. Our data showed that SD-P significantly increase rhizosheath weight in white lupin. Among the root segments, MCR showed improved P accumulation in the root which is associated with increased MCR rhizosheath weight. Additionally, a positive correlation was observed between MCR rhizosheath weight and P uptake. Moreover, high sucrose content was recorded in MCR, which may contribute in CR growth under SD-P. Expression analysis of genes related to sucrose accumulation (LaSUC1, LaSUC5, and LaSUC9) and phosphorus uptake (LaSPX3, LaPHO1, and LaPHT1) exhibited peaked expression in MCR under SD-P. This indicate that root sucrose status may facilitate P uptake under P starvation. Together, the ability to enhance P uptake of white lupin is largely associated with MCR rhizosheath under SD-P. Our results showed that gene expression modulation of CR forming plant species, demonstrating that these novel root structures may play crucial role in P acquisition from the soil. Our findings could be implicated for developing P and water efficient crop via CR development in sustainable agriculture.

Keywords: Cluster roots; P deficient; P uptake; Rhizosheath; Soil drying; White lupin.