SUMMARY
IQ Domain 1 (IQD1) is a novel calmodulin-binding protein in A. thaliana, which was found to be a positive regulator of glucosinolate (GS) accumulation and plant defense responses against insects. We demonstrate here that the IQD1 overexpressing line (IQD1OXP) is more resistant also to the necrotrophic fungus Botrytis cinerea, whereas an IQD1 knockout line (iqd1-1) is much more sensitive. Furthermore, we show that IQD1 is upregulated by Jasmonic acid (JA) and downregulated by Salicylic acid (SA). Comparison of whole transcriptome expression between iqd1-1 and wild type revealed a substantial downregulation of genes involved in plant defense and hormone regulation. Further examination revealed a marked reduction of SA/JA signaling and increase in ethylene signaling genes in the iqd1-1 line. Moreover, quantification of SA, JA and abscisic acids in IQD1OXP and iqd1-1lines compared to WT showed a significant reduction in endogenous JA levels in the knockout line simultaneously with increased SA levels. Epistasis relations between IQD1OXP and mutants defective in plant-hormone signaling indicated that IQD1 acts upstream or parallel to the hormonal pathways (JA/ET and SA) in defense response against B. cinerea and in regulating GS accumulation and it is dependent on JAR1 controlling indole glucosinolate accumulation. As a whole, our results suggest that IQD1 is an important defensive protein against Botrytis cinerea in A. thaliana and is integrated into several important pathways such as plant microbe perception and hormone signaling.
SIGNIFICANCE STATEMENT IQD1 is involved in glucosinolate accumulation and in general defense responses. JA activates IQD1 that acts upstream or parallel to JA/ET and SA signaling pathway while controlling glucosinolate accumulation and defense against Botrytis cinerea and it is dependent on JAR1 controlling indole glucosinolate accumulation.
Competing Interest Statement
The authors have declared no competing interest.