Arabidopsis lines with modified ascorbate concentrations reveal a link between ascorbate and auxin biosynthesis
Authors: Fenech, M., Zulian, V., Moya-Cuevas, J., Arnaud, D., Morilla, I., Smirnoff, N., Botella, M. A., Stepanova, A. N., Alonso, J. M., Martin-Pizarro, C., Amorim-Silva, V.
The study used Arabidopsis thaliana mutants with low (vtc2, vtc4) and high (vtc2/OE-VTC2) ascorbate levels to examine how ascorbate concentration affects gene expression and cellular homeostasis. Transcriptomic analysis revealed that altered ascorbate levels modulate defense and stress pathways, and that TAA1/TAR2‑mediated auxin biosynthesis is required for coping with elevated ascorbate in a light‑dependent manner.
The study characterizes the tomato class B heat shock factor SlHSFB3a, revealing its age‑dependent expression in roots and its role in enhancing lateral root density by modulating auxin homeostasis. Overexpression of SlHSFB3a increases lateral root emergence, while CRISPR‑mediated knockouts produce the opposite phenotype, indicating that SlHSFB3a regulates auxin signaling through repression of auxin repressors and activation of the ARF7/LOB20 pathway.
A biparental Vicia faba mapping population was screened under glasshouse conditions for resistance to a mixture of Fusarium avenaceum and Fusarium oxysporum, revealing several families with moderate to high resistance. Using the Vfaba_v2 Axiom SNP array, a high-density linkage map of 6,755 SNPs was constructed, enabling the identification of a major QTL on linkage group 4 associated with partial resistance to foot and root rot.
The study shows that silencing of NOR2 rRNA genes in Arabidopsis thaliana depends primarily on CHH-context cytosine methylation, particularly mediated by CMT2 and the chromatin remodeler DDM1, rather than CG or CHG methylation. Comparative promoter analysis revealed a prevalence of CHH sites in plant rDNA promoters, explaining why CHH methylation mutants disrupt NOR2 silencing more strongly, while NOR2 loci are hyper‑methylated and more condensed than NOR4.