The phosphate transporters LjPT4 and MtPT4 mediate early root responses to phosphate status in non mycorrhizal roots

Abstract

Arbuscular mycorrhizal (AM) symbiosis improves host plant phosphorous (P) status and elicits the expression of AM-inducible phosphate transporters (PTs) in arbuscule-containing cells, where they control arbuscule morphogenesis and P release. We confirmed such functions for LjPT4 in mycorrhizal Lotus japonicus. Promoter-GUS experiments showed LjPT4 transcription not only in arbusculated cells but also in root tips, in the absence of the fungus: here LjPT4 transcription profile depended on the phosphate level. In addition, quantitative RT-PCR confirmed the expression of Lotus and Medicago truncatula PT4 in the tips of non-mycorrhizal roots. Starting from these observations, we hypothesized that AM-inducible PTs may have a regulatory role in plant development, irrespective of the fungal presence. Firstly, we focused on root development responses to different phosphate treatments in both plants demonstrating that phosphate starvation induced a higher number of lateral roots. By contrast, Lotus PT4i plants and Medicago mtpt4 mutants did not show any differential response to phosphate levels, suggesting that PT4 genes affect early root branching. Phosphate starvation-induced genes and a key auxin receptor, MtTIR1, showed an impaired expression in mtpt4 plants. We suggest PT4 genes as novel components of the P-sensing machinery at the root tip level, independently of AM fungi.

NIN Is Involved in the Regulation of Arbuscular Mycorrhizal Symbiosis

“…We also checked the expression of some marker genes such as the R. irregularis tubulin and the plant VAPYRIN gene, coding for a protein involved in vesicle trafficking during mycorrhization, essential for arbuscule formation and for efficient epidermal penetration of AM fungi (Pumplin et al, 2010). To ensure the good functionality of arbuscules, we assayed the expression of a phosphate transporter MtPt4 , up-regulated during mycorrhization and necessary for the development of fully active arbuscules (Harrison et al, 2002; Volpe et al, 2016). Confirming the reduced mycorrhizal phenotype, fungal development markers were less expressed in Mtnin-1 mutant reflecting the general lower mycorrhization rate in these plants ( Figure 3 ).…”

A Review of Methods to Improve Nitrogen Use Efficiency in Agriculture

“…Leguminous crops have a high NUE because they gather and store nitrogen in their bodies rather than release it into the atmosphere [11,12]. There is still much debate, however, as to whether the net loss of nitrogen is less with legumes than with other crops, as some is lost during decomposition of both leguminous and other crops [19]. NUE measures how much nitrogen a plant uptakes as well as how much of this nitrogen uptake is lost via nitrous oxide emissions from the plants.…”

Phosphate Treatment Strongly Inhibits New Arbuscule Development But Not the Maintenance of Arbuscule in Mycorrhizal Rice Roots

“…Consistent with this, pt11-1 was more sensitive to P inhibition than that of the wild type, suggesting that P uptake through PT11 in colonized cells stabilizes arbuscules during P inhibition. Alternatively, PT11 in arbuscule-containing cells may act as a component of P-sensing machinery as proposed in the root tips of M. truncatula and Lotus japonicas (Volpe et al, 2016).…”