NITROGEN LIMITATION ADAPTATION functions as a negative regulator of Arabidopsis immunity

Abstract

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 response to pathogen infection. However, cross-talk between phosphate signaling pathways and immune responses remains unclear. Results: In this study, we investigated whether NLA plays a role in Arabidopsis immunity. We show that loss-of-function of NLA and MIR827 overexpression causes an increase in phosphate (Pi) content which results in resistance to infection by the fungal pathogen Plectosphaerella cucumerina. The nla mutant 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 of MIR827 and down-regulation of NLA. Upon pathogen challenge, nla plants 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, the nla mutant 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 that NLA acts as a negative regulator of Arabidopsis immunity. Overaccumulation of Pi in nla plants 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.

To have or not to have: expression of amino acid transporters during pathogen infection

“…Overexpression of AtCPK1 leads to increased resistance of plants upon necrotrophic attack, the molecular regulation for this is, however, so far unknown (Coca and San Segundo 2010 ). The suggested downregulation of AtNLA upon necrotrophic interaction (Val-Torregrosa et al 2021 -preprint) would lead to a potential reduction in AtORE1 degradation. Overall, this would increase AtORE1 activity and PCD as well as senescence (Oh et al 1997 ; Kim et al 2009 ; Balazadeh et al 2010 ; Farage-Barhom et al 2011 ; Al-Daoud and Cameron 2011 ; Matallana-Ramirez et al 2013 ; Qiu et al 2015 ; Durian et al 2020 ).…”

“…Interestingly, also plants infected with necrotrophs displayed increased resistance, although no ET derived defense responses were found (Coca and San Segundo 2010 ). In a preprinted study, it was suggested that AtNLA displays a negative regulator in plant defense against necrotrophs (Val-Torregrosa et al 2021 -preprint). nla mutants displayed increased callose deposition as well as increased resistance.…”

“…nla mutants displayed increased callose deposition as well as increased resistance. Upon pathogen attack, transcript levels of AtNLA were reduced (Val-Torregrosa et al 2021 -preprint).…”