THESEUS1 positively modulates plant defense responses against Botrytis cinerea through GUANINE EXCHANGE FACTOR4 signaling

The plant cell wall is an important interface for sensing pathogen attack and activating signaling pathways that promote plant immune responses.THESEUS1(THE1) acts as a sensor of cell wall integrity that controls cell elongation during plant growth.However, no specific role for THE1 in plant defense responses has been reported. Here, we found that THE1 interacts with GUANINE EXCHANGE FACTOR4(GEF4)and that both proteins play regulatory roles in plant resistance to the necrotrophic fungus Botrytis cinerea.Genetic analysis showed that THE1 and GEF4 function in the same genetic pathway to mediate plant defense responses. In addition, using transcriptome analysis, we identified various genes(such as defense-related,secondary metabolite-related, and transcription factor genes) that are likely downstream targets in the THE1-GEF4 signaling pathway. Our results suggest that THE1 functions as an upstream regulator of GEF4 signaling to positively regulate defense responses against B. cinerea in Arabidopsis.

Nitrogen starvation induces genome-wide activation of transposable elements in Arabidopsis

Nitrogen(N)availability is a major limiting factor for plant growth and agricultural productivity.Although the gene regulation network in response to N starvation has been extensively studied,it remains unknown whether N starvation has an impact on the activity of transposable elements(TEs).Here,we report that TEs can be transcriptionally activated in Arabidopsis under N starvation conditions.Through genetic screening of idm1-14 suppressors,we cloned GLU1,which encodes a glutamate synthase that catalyzes the synthesis of glutamate in the primary N assimilation pathway.We found that glutamate synthase 1(GLU1)and its functional homologs GLU2 and glutamate transport 1(GLT1)are redundantly required for TE silencing,suggesting that N metabolism can regulate TE activity.Transcriptome and methylome analyses revealed that N starvation results in genome-wide TE activation without inducing obvious alteration of DNA methylation.Genetic analysis indicated that N starvationinduced TE activation is also independent of other well-established epigenetic mechanisms,including histone methylation and heterochromatin decondensation.Our results provide new insights into the regulation of TE activity under stressful environments in planta.