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In the summer of 2021, we held a community workshop at the International Congress of Arabidopsis Research (ICAR) aimed at early career researchers and focused on values-based lab leadership. Here, we elaborate on ideas emerging from the workshop that we hope will allow current and future group leaders to reflect on and adjust to the rapidly evolving nature of the academic scientific enterprise. [ABSTRACT FROM AUTHOR]

Nutrient uptake is critical for crop growth and is determined by root foraging in soil. Growth and branching of roots lead to effective root placement to acquire nutrients, but relatively little is known about absorption of nutrients at the root surface from the soil solution. This knowledge gap could be alleviated by understanding sources of genetic variation for short-term nutrient uptake on a root length basis. A modular platform called RhizoFlux was developed for high-throughput phenotyping of multiple ion-uptake rates in maize (Zea mays L.). Using this system, uptake rates were characterized for the crop macronutrients nitrate, ammonium, potassium, phosphate, and sulfate among the Nested Association Mapping (NAM) population founder lines. The data revealed substantial genetic variation for multiple ion-uptake rates in maize. Interestingly, specific nutrient uptake rates (nutrient uptake rate per length of root) were found to be both heritable and distinct from total uptake and plant size. The specific uptake rates of each nutrient were positively correlated with one another and with specific root respiration (root respiration rate per length of root), indicating that uptake is governed by shared mechanisms. We selected maize lines with high and low specific uptake rates and performed an RNA-seq analysis, which identified key regulatory components involved in nutrient uptake. The high-throughput multiple ion-uptake kinetics pipeline will help further our understanding of nutrient uptake, parameterize holistic plant models, and identify breeding targets for crops with more efficient nutrient acquisition. [ABSTRACT FROM AUTHOR]

Since 1999, various forward- and reverse-genetic approaches have uncovered nearly 200 genes required for symbiotic nitrogen fixation (SNF) in legumes. These discoveries advanced our understanding of the evolution of SNF in plants and its relationship to other beneficial endosymbioses, signaling between plants and microbes, the control of microbial infection of plant cells, the control of plant cell division leading to nodule development, autoregulation of nodulation, intracellular accommodation of bacteria, nodule oxygen homeostasis, the control of bacteroid differentiation, metabolism and transport supporting symbiosis, and the control of nodule senescence. This review catalogs and contextualizes all of the plant genes currently known to be required for SNF in two model legume species, Medicago truncatula and Lotus japonicus , and two crop species, Glycine max (soybean) and Phaseolus vulgaris (common bean). We also briefly consider the future of SNF genetics in the era of pan-genomics and genome editing. [ABSTRACT FROM AUTHOR]

Most legume plants can form nodules, specialized lateral organs that form on roots, and house nitrogen-fixing bacteria collectively called rhizobia. The uptake of the phytohormone auxin into cells is known to be crucial for development of lateral roots. To test the role of auxin influx in nodulation we used the auxin influx inhibitors 1-naphthoxyacetic acid (1-NOA) and 2-NOA, which we found reduced nodulation of Medicago truncatula. This suggested the possible involvement of the AUX/LAX family of auxin influx transporters in nodulation. Gene expression studies identified MtLAX2, a paralogue of Arabidopsis (Arabidopsis thaliana) AUX1, as being induced at early stages of nodule development. MtLAX2 is expressed in nodule primordia, the vasculature of developing nodules, and at the apex of mature nodules. The MtLAX2 promoter contains several auxin response elements, and treatment with indole-acetic acid strongly induces MtLAX2 expression in roots. mtlax2 mutants displayed root phenotypes similar to Arabidopsis aux1 mutants, including altered root gravitropism, fewer lateral roots, shorter root hairs, and auxin resistance. In addition, the activity of the synthetic DR5-GUS auxin reporter was strongly reduced in mtlax2 roots. Following inoculation with rhizobia, mtlax2 roots developed fewer nodules, had decreased DR5-GUS activity associated with infection sites, and had decreased expression of the early auxin responsive gene ARF16a. Our data indicate that MtLAX2 is a functional analog of Arabidopsis AUX1 and is required for the accumulation of auxin during nodule formation in tissues underlying sites of rhizobial infection. [ABSTRACT FROM AUTHOR]

CYTOKININ AND THE ESTABLISHMENT OF A RESEARCH PROGRAM Wanting to challenge himself further, Kieber gradually turned towards another classic hormone, cytokinin, for which the underlying molecular signals were relatively unstudied even though the physiological responses were very well known. Graph At the crux of understanding plant biology lies the intricate hormone circuitry coordinating morphological and physiological changes as plants grow and adapt to their environment. While performing a BLAST search, Kieber found that the locus to which I CTR1 i mapped had a gene encoding a protein with high homology to members of the Raf-1 kinase family, suggesting that it was a protein kinase. Kieber and his student, Ingrid Brandstatter, suggested that these proteins were involved in early cytokinin signal transduction ([1]); Kieber spent the next two decades investigating and proving this hypothesis correct. [Extracted from the article]

Nitrogen-fixing rhizobia colonize legume roots via plant-made intracellular infection threads. Genetics has identified some genes involved but has not provided sufficient detail to understand requirements for infection thread development. Therefore, we transcriptionally profiled Medicago truncatula root hairs prior to and during the initial stages of infection. This revealed changes in the responses to plant hormones, most notably auxin, strigolactone, gibberellic acid, and brassinosteroids. Several auxin responsive genes, including the ortholog of Arabidopsis thaliana Auxin Response Factor 16 , were induced at infection sites and in nodule primordia, and mutation of ARF16a reduced rhizobial infection. Associated with the induction of auxin signaling genes, there was increased expression of cell cycle genes including an A-type cyclin and a subunit of the anaphase promoting complex. There was also induction of several chalcone O -methyltransferases involved in the synthesis of an inducer of Sinorhizobium meliloti nod genes, as well as a gene associated with Nod factor degradation, suggesting both positive and negative feedback loops that control Nod factor levels during rhizobial infection. We conclude that the onset of infection is associated with reactivation of the cell cycle as well as increased expression of genes required for hormone and flavonoid biosynthesis and that the regulation of auxin signaling is necessary for initiation of rhizobial infection threads. [ABSTRACT FROM AUTHOR]

The cephalochordate, amphioxus, is phylogenetically placed at the most primitive position in the chordate clade. Despite many studies on the endocrine system of amphioxus, definitive evidence has not been reported for the presence an endocrine system comparable to the pituitary–gonadal axis, which is important in the regulation of reproduction in vertebrates. Recent genome analyses in the amphioxus, Branchiostoma floridae, showed that it does not have any pituitary hormone genes except the thyrostimulin gene. Thyrostimulin is a heterodimeric glycoprotein hormone consisting of α and β subunits, and is present in various organs of vertebrates. Analyses of a phylogenetic tree and a synteny suggest that amphioxus’ thyrostimulin is an ancestral type of the glycoprotein hormones in chordates. In addition, genes for sex steroidogenic enzymes belonging to the CYP family were found in the genome sequences. The conversion pathway of sex steroids from cholesterol to estrogen, androgen, and major sex steroids was also identified in the gonads of amphioxus in vitro. Furthermore, we demonstrated the expression of genes encoding thyrostimulin and sex steroidogenic enzymes by an in situ hybridization technique. Here, we discuss the evolution of hormones and reproductive functions in the neuroendocrine control system of chordates. [ABSTRACT FROM PUBLISHER]

The authors further dissect the I NIN i promoter and reveal that it is roughly modular; I NIN i expression driven by up to 2.2 kb of the promoter can rescue excessive rhizobia-responsive root hair curling and infection-pocket formation, while 5 kb can restore defects in infection thread development. However, if the I NIN i promoter region is disrupted, as in the I L. japonicus daphne i mutant, only nodule organogenesis is abolished and instead the mutants are hyperinfected ([5]). [Extracted from the article]

Therefore, in heterogonous nitrate environments, nitrate-inducible I IPT3 i and I IPT5 i genes can affect overall plant development by controlling biosynthesis of different active forms of CK including I trans i -zeatin ([3]). Shoot Cytokinin Signals Integrate Growth Responses with Nitrogen Availability Under these conditions, the authors compared the patterns of CK accumulation and associated transcriptional responses of the roots and shoots of wild-type plants to the CK biosynthetic and transport mutants I ipt3,5,7 i and I abcg14 i , respectively. [Extracted from the article]

Consistent with its localization in infection chambers of curled root hairs, mutants in this chitinase-like hydrolase gene had fewer infection events and the root hairs showed aberrant branching. The authors hypothesized that, since accumulation of uncleaved NFs resulting from a lack of NF hydrolase activity caused aberrant organogenesis, overproduction of NFs must similarly affect nodule morphology. [Extracted from the article]

The lipid-derived hormone jasmonic acid (JA) is one such component of a robust plant immune system that regulates gene expression in response to pathogens and insects. Understanding hormone action requires a detailed insight into the underlying gene network that effects rapid signaling to bring about changes in plant metabolism, including but not limited to, biosynthesis of defense-related proteins and secondary metabolites. Subsequent RNA-seq on I myb48 myb59 i revealed 399 DEGs, with key JA-responsive biosynthesis and marker genes, such as I VSP2 i , showing significantly higher expression in the mutant. [Extracted from the article]