Garcia, R. R. | bioRxiv Science

bioRxiv2023

TML1 AND TML2 SYNERGISTICALLY REGULATE NODULATION BUT NOT ARBUSCULAR MYCORRHIZA IN MEDICAGO TRUNCATULA

Two symbiotic processes, nodulation and arbuscular mycorrhiza, are primarily controlled by the plants need for nitrogen (N) and phosphorus (P), respectively. Autoregulation of Nodulation (AON) and Autoregulation of Mycorrhization (AOM) both negatively regulate their respective processes and share multiple components - plants that make too many nodules usually have higher AM fungal root colonization. The protein TML (TOO MUCH LOVE) was shown to function in roots to maintain susceptibly to rhizobial infection under low N conditions and control nodule number through AON in Lotus japonicus. M. truncatula has two sequence homologs: MtTML1 and MtTML2. We report the generation of stable single and double mutants harboring multiple allelic variations in MtTML1 and MtTML2 using CRISPR-Cas9 targeted mutagenesis and screening of a transposon mutagenesis library. Plants containing single mutations in MtTML1 or MtTML2 produced 2-3 times the nodules of wild-type plants whereas plants containing mutations in both genes displayed a synergistic effect, forming 20x more nodules compared to wild type plants. Examination of expression and heterozygote effects suggest genetic compensation may play a role in the observed synergy. Plants with mutations in both TMLs only showed mild increases in AM fungal root colonization at later timepoints in our experiments, suggesting these genes may also play a minor role in AM symbiosis regulation. The mutants created will be useful tools to dissect the mechanism of synergistic action of MtTML1 and MtTML2 in M. truncatula symbiosis with beneficial microbes.

molecular biology↗

bioRxiv2023

Human adolescent brain network development is different for paralimbic versus neocortical systems

Adolescent development of human brain structural and functional networks is increasingly recognised as fundamental to emergence of typical and atypical adult cognitive and emotional processes. We analysed multimodal magnetic resonance imaging (MRI) data collected from N [~] 300 healthy adolescents (51%; female; 14-26 years) each scanned repeatedly in an accelerated longitudinal design, to provide an analyzable dataset of 469 structural scans and 448 functional MRI scans. We estimated the morphometric similarity between each possible pair of 358 cortical areas on a feature vector comprising six macro- and micro-structural MRI metrics, resulting in a morphometric similarity network (MSN) for each scan. Over the course of adolescence, we found that morphometric similarity increased in paralimbic cortical areas, e.g., insula and cingulate cortex, but generally decreased in neocortical areas; and these results were replicated in an independent developmental MRI cohort (N [~] 304). Increasing hubness of paralimbic nodes in MSNs was associated with increased strength of coupling between their morphometric similarity and functional connectivity. Decreasing hubness of neocortical nodes in MSNs was associated with reduced strength of structure-function coupling and increasingly diverse functional connections in the corresponding fMRI networks. Neocortical areas became more structurally differentiated and more functionally integrative in a metabolically expensive process linked to cortical thinning and myelination; whereas paralimbic areas specialised for affective and interoceptive functions became less differentiated, as hypothetically predicted by a developmental transition from peri-allocortical to pro-isocortical organization of cortex. Cytoarchitectonically distinct zones of human cortex undergo distinct neurodevelopmental programmes during typical adolescence.

neuroscience↗