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Background

Phosphorus is an important macronutrient required for plant growth and development. It is absorbed through the roots in the form of inorganic phosphate (Pi). To cope with Pi limitation, plants have evolved an array of adaptive mechanisms to facilitate Pi acquisition and protect them from stress caused by Pi starvation. The NITROGEN LIMITATION ADAPTION (NLA) gene plays a key role in the regulation of phosphate starvation responses (PSR), its expression being regulated by the microRNA miR827. Stress caused by Pi limiting conditions might also affect the plant’s response to pathogen infection. However, cross-talk between phosphate signaling pathways and immune responses remains unclear.

Results

In this study, we investigated whetherNLAplays a role in Arabidopsis immunity. We show that loss-of-function ofNLAandMIR827overexpression causes an increase in phosphate (Pi) content which results in resistance to infection by the fungal pathogenPlectosphaerella cucumerina. Thenlamutant plants accumulated callose in their leaves, a response that is also observed in wild-type plants that have been treated with high Pi. We also show that pathogen infection and treatment with fungal elicitors is accompanied by transcriptional activation ofMIR827and down-regulation ofNLA. Upon pathogen challenge,nlaplants exhibited higher levels of the phytoalexin camalexin compared to wild type plants. Camalexin level also increases in wild type plants treated with high Pi. Furthermore, thenlamutant plants accumulated salicylic acid (SA) and jasmonic acid (JA) in the absence of pathogen infection whose levels further increased upon pathogen.

Conclusions

This study shows thatNLAacts as a negative regulator of Arabidopsis immunity. Overaccumulation of Pi innlaplants positively affects resistance to infection by fungal pathogens. This piece of information reinforces the idea of signaling convergence between Pi and immune responses for the regulation of disease resistance in Arabidopsis.