Jasmonate and aluminum crosstalk in tomato: Identification and expression analysis of WRKYs and ALMTs during JA/Al-regulated root growth

The WRKY transcription factors (TFs) are involved in aluminum (Al) stress and jasmonic acid (JA)-regulated resistance responses. WRKYs act as regulators of Al-activated malate transporter (ALMT) proteins (anion channels) by directly binding to their promoters and altering malate efflux, thereby regulating Al ion toxicity in plant roots. JA enhances Al-induced root growth inhibition in Arabidopsis. However, the relationship between WRKY and ALMT genes and their involvement in JA-mediated root growth inhibition during Al stress in tomato remain unknown. Here, we demonstrate a similar phenomenon that JA enhances Al-induced root growth inhibition in tomato (Solanum lycopersicum). By analyzing RNA-seq data and tissue-specific expression data from public databases, we selected 17 WRKY and 6 ALMT family genes to identify the genes participated in this process. The promoters of many of the selected genes contained MeJA responsive element, G-box (target site of MYC2, a core TF of JA signaling), and W-box (target site for WRKY). Quantitative real-time PCR was performed to evaluate the expression levels of selected WRKY and ALMT genes under AlCl3 and Methyl jasmonate (MeJA) treatment. SlMYC2-VIGS seedlings and jasmonic acid-insensitive1 (jai1) mutant were also employed to analyze the expression patterns of selected genes. We find that SlALMT3 is responsible for the crosstalk regulatory mechanism between Al and JA in root growth inhibition, and 6 SlWRKYs may act as the upstream regulators of SlALMT3 in this crosstalk response. This study is initial and informative in exploring the crosstalk regulatory mechanism between JA and Al in tomato.