Partnership for callusing

Glucosinolate O-methyltransferase mediated callus formation and affected ROS homeostasis in Arabidopsis thaliana

Auxin-induced callus formation was largely dependent on the function of Lateral Organ Boundaries Domain (LBD) family transcription factors. We previously revealed that two IGMT (Indole glucosinolate oxy-methyl transferase) genes, IGMT2 and IGMT3, may be involved in the callus formation process as potential target genes of LBD29. Overexpression of the IGMT genes induces spontaneous callus formation. However, the details of the IGMT involvement in callus formation process were not well studied. IGMT1-4, but not IGMT5, are targeted and induced by LBD29 during the early stage of callus formation. Cell membrane and nucleus localized IGMT3 was mainly expressed in the elongation and maturation zones tissues of the primary root and lateral root, which could be further accumulated after CIM treatment. The igmts quadruple mutant, which obtained by CRISPR/Cas9 technology, exhibits a phenotype of attenuated callus formation. Enhanced indole glucosinolate anabolic pathway caused by IGMT1-4 overexpression promotes callus formation. In addition, the IGMT genes were involved in the reactive oxygen species homeostasis, which could be responsible for its role on callus formation. This study provides novel insights into the role of IGMTs gene-mediated callus formation. Activation of the Indole glucosinolate anabolic pathway is an inducing factor for plant callus initiation.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12298-023-01409-2.

Transcriptional activation by WRKY23 and derepression by removal of bHLH041 coordinately establish callus pluripotency in Arabidopsis regeneration

Induction of the pluripotent cell mass termed callus from detached organs or tissues is an initial step in typical in vitro plant regeneration, during which auxin-induced ectopic activation of root stem cell factors is required for subsequent de novo shoot regeneration. While Arabidopsis (Arabidopsis thaliana) AUXIN RESPONSE FACTOR 7 (ARF7) and ARF19 and their downstream transcription factors LATERAL ORGAN BOUNDARIES DOMAIN (LBD) are known to play key roles in directing callus formation, the molecules responsible for activation of root stem cell factors and thus establishment of callus pluripotency are unclear. Here, we identified Arabidopsis WRKY23 and BASIC HELIX-LOOP-HELIX 041 (bHLH041) as a transcriptional activator and repressor, respectively, of root stem cell factors during establishment of auxin-induced callus pluripotency. We show that auxin-induced WRKY23 downstream of ARF7 and ARF19 directly activates the transcription of PLETHORA 3 (PLT3) and PLT7 and thus that of the downstream genes PLT1, PLT2, and WUSCHEL-RELATED HOMEOBOX 5 (WOX5), while LBD-induced removal of bHLH041 derepresses the transcription of PLT1, PLT2, and WOX5. We provide evidence that transcriptional activation by WRKY23 and loss of bHLH041-imposed repression act synergistically in conferring shoot-regenerating capability on callus cells. Our findings thus disclose a transcriptional mechanism underlying auxin-induced cellular reprogramming, which, together with previous studies, outlines the molecular framework of auxin-induced pluripotent callus formation for in vitro plant regeneration programs.

Plants make galls to accommodate foreigners: some are friends, most are foes

At the colonization site of a foreign entity, plant cells alter their trajectory of growth and development. The resulting structure - a plant gall - accommodates various needs of the foreigner, which are phylogenetically diverse: viruses, bacteria, protozoa, oomycetes, true fungi, parasitic plants, and many types of animals, including rotifers, nematodes, insects, and mites. The plant species that make galls also are diverse. We assume gall production costs the plant. All is well if the foreigner provides a gift that makes up for the cost. Nitrogen-fixing nodule-inducing bacteria provide nutritional services. Gall wasps pollinate fig trees. Unfortunately for plants, most galls are made for foes, some of which are deeply studied pathogens and pests: Agrobacterium tumefaciens, Rhodococcus fascians, Xanthomonas citri, Pseudomonas savastanoi, Pantoea agglomerans, 'Candidatus' phytoplasma, rust fungi, Ustilago smuts, root knot and cyst nematodes, and gall midges. Galls are an understudied phenomenon in plant developmental biology. We propose gall inception for discovering unifying features of the galls that plants make for friends and foes, talk about molecules that plants and gall-inducers use to get what they want from each other, raise the question of whether plants colonized by arbuscular mycorrhizal fungi respond in a gall-like manner, and present a research agenda.