Identification of novel genes involved in phosphate accumulation in Lotus japonicusthrough Genome Wide Association mapping of root system architecture and anion content.

Marco Giovannetti,Stanislav Kopriva,Wolfgang Busch,Stig U Andersen,Christof Dietzen,Christian Göschl,Caroline Gutjahr

doi:10.1371/journal.pgen.1008126

Abstract

Phosphate represents a major limiting factor for plant productivity. Plants have evolved different solutions to adapt to phosphate limitation ranging from a profound tuning of their root system architecture and metabolic profile to the evolution of widespread mutualistic interactions. Here we elucidated plant responses and their genetic basis to different phosphate levels in a plant species that is widely used as a model for AM symbiosis: Lotus japonicus. Rather than focussing on a single model strain, we measured root growth and anion content in response to different levels of phosphate in 130 Lotus natural accessions. This allowed us not only to uncover common as well as divergent responses within this species, but also enabled Genome Wide Association Studies by which we identified new genes regulating phosphate homeostasis in Lotus. Among them, we showed that insertional mutants of a cytochrome B5 reductase and a Leucine-Rich-Repeat receptor showed different phosphate concentration in plants grown under phosphate sufficient condition. Under low phosphate conditions, we found a correlation between plant biomass and the decrease of plant phosphate concentration in plant tissues, representing a dilution effect. Altogether our data of the genetic and phenotypic variation within a species capable of AM complements studies that have been conducted in Arabidopsis, and advances our understanding of the continuum of genotype by phosphate level interaction existing throughout dicot plants.

Highlights

Phosphate is an essential element for plant growth and its bioavailability represents a major limiting factor for plant productivity
To study the genetic bases of root responses to low phosphate and phosphate accumulation in Lotus japonicus (Lotus) tissues, we performed a detailed root phenotyping of a panel of 130 diverse Lotus natural accessions [23] over a 9-day time course and subsequently quantified anions of the main macronutrients from the same material (Fig 1A)
With the exception of phosphate concentration of plants grown under phosphate starvation, the concentration of these anions did neither depend on plant size nor on plant developmental stage (S1 Fig)

Summary

Introduction

Phosphate is an essential element for plant growth and its bioavailability represents a major limiting factor for plant productivity. It has been shown that a main driver of primary root growth arrest is toxicity of iron that, upon phosphate starvation, accumulates in the meristematic zone and induces a progressive loss in the proliferative capacity of the cells, causing reduction in meristem length [4]. Beside this strong local effect at the root tip, phosphate deficiency has a dramatic systemic effect causing a general remodeling of main cellular processes, mainly orchestrated by a transcriptomic cascade orchestrated by the interaction between PHR1 [5,6] and its SPX interactors [7,8,9]. Responses to phosphate and phosphate homeostasis in plants are regulated in a complex manner and are substantially dependent on plant genetic diversity and environmental abiotic and biotic factors

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Discussion

Conclusion