Biology subjects

DeLeon, A.

Publications and source records attributed to DeLeon, A..

3 recordsLinked to original sources

bioRxiv2020

Host auxin machinery is important in mediating root architecture changes induced by Pseudomonas fluorescens GM30 and Serendipita indica

Auxin is a key phytohormone that is integral to plant developmental processes including those underlying root initiation, elongation, and branching. Beneficial microbes have been shown to have an impact on root development, potentially mediated through auxin. In this study, we explore the role of host auxin signaling and transport components in mediating the root growth promoting effects of beneficial microbes. Towards this end, we undertook co-culture studies of Arabidopsis thaliana plants with microbes previously reported to promote lateral root proliferation and produce auxin. Two types of beneficial microbes were included in the present study; a plant growth promoting bacterial species of interest, Pseudomonas fluorescens GM30, and a well-studied plant growth promoting fungal species, Serendipita indica (Piriformospora indica). Following co-culture, lateral root production was found restored in auxin transport inhibitor-treated plants, suggesting involvement of microbe and/or microbially-produced auxin in altering plant auxin levels. In order to clarify the role of host auxin signaling and transport pathways in mediating interactions with bacterial and fungal species, we employed a suite of auxin genetic mutants as hosts in co-culture screens. Our result show that the transport proteins PIN2, PIN3, and PIN7 and the signaling protein ARF19, are required for mediating root architecture effects by the bacterial and/or fungal species. Mutants corresponding to these proteins did not significantly respond to co-culture treatment and did not show increases in lateral root production and lateral root density. These results implicate the importance of host auxin signaling in both bacterial and fungal induced changes in root architecture and serve as a driver for future research on understanding the role of auxin-dependent and auxin-independent pathways in mediating plant-microbe interactions in economically important crop species.

plant biology↗

bioRxiv2018

Thyroid hormone modulation during zebrafish development recapitulates evolved diversity in danionin jaw protrusion mechanics

One of three vertebrates belongs to a fish lineage for which protrusile jaws are a synapomorphy. Identifying the developmental determinants of protrusion ability will improve our understanding of an important area of evolutionary diversification. The high water viscosities experienced by tiny fish larvae inhibit the viability of protrusile jaws. In the zebrafish protrusion does not arise until after metamorphosis. Fish metamorphosis typically includes significant changes in trophic morphology, accompanies a shift in feeding niche and coincides with increased thyroid hormone production. We tested whether thyroid hormone affects the development of zebrafish feeding mechanics. We found that it affected all developmental stages examined, but that these effects were most pronounced after metamorphosis. Thyroid hormone levels affected the development of jaw morphology, feeding mechanics, shape variation and cranial ossification. Adult zebrafish utilize protrusile jaws, but an absence of thyroid hormone eliminated postmetamorphic remodeling of the premaxilla and the premaxillary structure that permits protrusion never formed. The premaxillae of late juvenile and adult zebrafish are similar to those found in the adults of other Danio species. Premaxillae from early juvenile zebrafish and hypothyroid adult zebrafish resemble those from adults in the genera Danionella, Devario and Microdevario that show little to no jaw protrusion.

developmental biology↗

bioRxiv2018

Adult Plant Resistance in Maize to Northern Leaf Spot Is a Feature of Partial Loss-of-function Alleles of Hm1

Adult plant resistance (APR) is an enigmatic phenomenon in which resistance genes are ineffective in protecting seedlings from disease but confer robust resistance at maturity. Maize has multiple cases in which genes confer APR to northern leaf spot, a lethal disease caused by Cochliobolus carbonum race 1 (CCR1). The first identified case of APR in maize is encoded by a hypomorphic allele, Hm1A, at the hm1 locus. In contrast, wild type alleles of hm1 provide complete protection at all developmental stages and in every part of the maize plant. Hm1 encodes an NADPH-dependent reductase, which inactivates HC-toxin, a key virulence effector of CCR1. Cloning and characterization of Hm1A ruled out differential transcription or translation for its APR phenotype and identified an amino acid substitution that reduced HC-toxin reductase (HCTR) activity. The possibility of a causal relationship between the weak nature of Hm1A and its APR phenotype was confirmed by the generation of two new APR alleles of Hm1 by mutagenesis. The HCTRs encoded by these new APR alleles had undergone relatively conservative missense changes that partially reduced their enzymatic activity similar to HM1A. No difference in accumulation of HCTR was observed between adult and juvenile plants, suggesting that the susceptibility of seedlings derives from a greater need for HCTR activity, not reduced accumulation of the gene product. Conditions and treatments that altered the photosynthetic output of the host had a dramatic effect on resistance imparted by the APR alleles, demonstrating a link between the energetic or metabolic status of the host and disease resistance affected by HC-toxin catabolism by the APR alleles of HCTR.\n\nAUTHOR SUMMARYAdult plant resistance (APR) is a phenomenon in which disease resistance genes are able to confer resistance at the adult stages of the plant but somehow fail to do so at the seedling stages. Despite the widespread occurrence of APR in various plant diseases, the mechanism underlying this trait remains obscure. It is not due to the differential transcription of these genes, and here we show that it is also not due to the differential translation or activity of the APR alleles of the maize hm1 gene at different stages of development. Using a combination of molecular genetics, biochemistry and physiology, we present multiple lines of evidence that demonstrate that APR is a feature or symptom of weak forms of resistance. While the mature parts of the plant are metabolically robust enough to manifest resistance, seedling tissues are not, leaving them vulnerable to disease. Growth conditions that compromise the photosynthetic output of the plant further deteriorate the ability of the seedlings to protect themselves from pathogens.\n\nOne sentence summaryCharacterization of adult plant resistance in the maize-CCR1 pathosystem reveals a causal link between weak resistance and APR.

pathology↗