Biology subjects

Martinez, S. E.

Publications and source records attributed to Martinez, S. E..

8 recordsLinked to original sources

bioRxiv2026

KATANIN is required for the formation of complete preprophase bands and subsequent division positioning of subsidiary mother cells in maize

Microtubule dynamics underpin cell division, movement, and growth in eukaryotic organisms. KATANIN p60 is a microtubule-severing protein that promotes proper cell elongation and division. In plants, division positioning is initiated in late G2 via the formation of a microtubule structure called the preprophase band (PPB). Maize p60 mutants have defects in microtubule severing and form abnormal PPBs in symmetrically dividing cells, including both incompletely assembled and misoriented PPBs. Here, we show that an asymmetric division required to generate stomatal complexes in maize p60 mutants have normally positioned but often incompletely formed PPBs. Incompletely formed PPBs lead to misoriented divisions and nuclear positioning defects in p60 mutants.

plant biology↗

bioRxiv2025

KATANIN promotes cell elongation and division to generate proper cell numbers in maize organs

Microtubule severing is essential for proper eukaryotic cell elongation and division. Here we show that the microtubule severing protein, KATANIN, is encoded by two genes in Zea mays (maize) called Discordia3a (Dcd3a) and Dcd3b. Loss of function allele combinations contribute to reduced microtubule severing and decreased cell elongation. The latter results in reduced cell number by slowing entry into mitosis. KATANIN is important for preprophase band (PPB) formation and positioning, and nuclear positioning in symmetric cell divisions. A combination of these defects contributes to generating mutant plants with small size and aberrant shape.

plant biology↗

bioRxiv2025

Recessive antimorph alleles reveal novel functions of the OPAQUE1 myosin XI in maize

Ideal plant architecture optimizes canopy structure and increases grain yield in maize. However, its underlying genetic mechanisms remain poorly characterized. Two recessive, EMS-induced maize mutants were identified that have reduced stature, opaque kernels, and abnormal subsidiary cell division, and are allelic to opaque1 (o1). These two new missense alleles, o1-2995 and o1-tan62, unlike the loss-of-function alleles previously identified, generate O1 protein but paradoxically generate more severe morphological defects. These defects include reduced internode elongation and partial suppression of excessive tassel and ear branching in ramosa1 (ra1), ra2, and ra3 mutants. We show that o1-2995 and o1-tan62 are novel alleles of o1, and play a role in plant growth via internode elongation, subsidiary cell division positioning, leaf patterning, inflorescence development, and overall plant architecture.

plant biology↗

bioRxiv2024

De Novo TANGLED1 Recruitment to Aberrant Cell Plate Fusion Sites in Maize

Division plane positioning is critical for proper growth and development in many organisms. In plants, the division plane is established before mitosis, by accumulation of a cytoskeletal structure called the preprophase band (PPB). The PPB is thought to be essential for recruitment of division site localized proteins, which remain at the division site after the PPB disassembles. Here, we show that a division site localized protein, TANGLED1 (TAN1), is recruited independently of the PPB to the cell cortex at sites, by the plant cytokinetic machinery, the phragmoplast. TAN1 recruitment to de novo sites on the cortex is partially dependent on intact actin filaments and the myosin XI motor protein OPAQUE1 (O1). These data imply a yet unknown role for TAN1 and possibly other division site localized proteins during the last stages of cell division when the phragmoplast touches the cell cortex to complete cytokinesis. Summary StatementThe plant division site protein TANGLED1 is recruited to de novo cell plate insertion sites independently of the preprophase band.

plant biology↗

bioRxiv2022

Cryo-EM structures of Doravirine and Rilpivirine with HIV-1 Reverse Transcriptase/DNA Aptamer: Nonnucleoside Inhibitor Resistance by E138K and M184I Mutations

Structures trapping a verity of functional and conformational states of HIV-1 reverse transcriptase (RT) have been determined by X-ray crystallography. These structures have played important roles in understanding the mechanisms of catalysis, inhibition and drug resistance, and in driving drug design. However, structures of several desired complexes of RT could not be obtained even after many crystallization or crystal soaking experiments. The ternary complexes of doravirine and rilpivirine with RT/DNA are such examples. Structural study of HIV-1 RT by single-particle cryo-EM has been challenging due to the enzymes relatively smaller size and higher flexibility. We optimized a protocol for rapid structure determination of RT complexes by cryo-EM and determined six structures of wild-type and E138K/M184I mutant RT/DNA in complexes with the nonnucleoside inhibitors rilpivirine, doravirine, and nevirapine. RT/DNA/rilpivirine and RT/DNA/doravirine complexes have structural differences between them and from the representative conformation of RT/DNA/nevirapine (or efavirenz); the primer grip in the RT/DNA/doravirine and the YMDD motif in the RT/DNA/rilpivirine complexes have large shifts. The DNA primer 3-end in the doravirine-bound structure is positioned at the active site, but the complex is in a non-productive state. In the mutant RT/DNA/rilpivirine structure, I184 is stacked with the DNA such that their relative positioning can influence rilpivirine in the pocket. Simultaneously, E138K mutation widens the NNRTI-binding pocket entrance, potentially contributing to a faster rate of rilpivirine dissociation by E138K/M184I mutant RT, as reported by earlier kinetic studies. These structural differences have implications for drug design and for understanding molecular mechanisms of drug resistance.

biophysics↗

bioRxiv2021

A KARRIKIN INSENSITIVE2 paralog in lettuce mediates highly sensitive germination responses to karrikinolide

Karrikins (KARs) are chemicals in smoke that can enhance germination of many plants. Lactuca sativa cv. Grand Rapids (lettuce), germinates in the presence of nanomolar karrikinolide (KAR1). We found that lettuce is much less responsive to KAR2 or a mixture of synthetic strigolactone analogs, rac-GR24. We investigated the molecular basis of selective and sensitive KAR1 perception in lettuce. The lettuce genome contains two copies of KARRIKIN INSENSITIVE2 (KAI2), a receptor that is required for KAR responses in Arabidopsis thaliana. LsKAI2b is more highly expressed than LsKAI2a in dry achenes and during early stages of seed imbibition. Through cross-species complementation assays in Arabidopsis we found that LsKAI2b confers robust responses to KAR1, but LsKAI2a does not. Therefore, LsKAI2b likely mediates KAR1 responses in lettuce. We compared homology models of the ligand-binding pockets of KAI2 proteins from lettuce and a fire follower, Emmenanthe penduliflora. This identified pocket residues 96, 124, 139, and 161 as candidates that influence the ligand-specificity of KAI2. Further support for the significance of these residues was found through a broader comparison of pocket residue conservation among 324 asterid KAI2 proteins. We tested the effects of substitutions at these four positions in Arabidopsis thaliana KAI2 and found that a broad array of responses to KAR1, KAR2, and rac-GR24 could be achieved.

plant biology↗

bioRxiv2021

Sliding of HIV-1 reverse transcriptase over DNA creates a transient P pocket - Targeting P-pocket by fragment screening

HIV-1 reverse transcriptase (RT) slides over an RNA/DNA or dsDNA substrate while copying the viral RNA to a proviral DNA. We report a crystal structure of RT/dsDNA complex in which RT overstepped the primer 3-end of a dsDNA substrate and created a transient P-pocket at the priming site. We performed a high-throughput screening of 300 drug-like fragments by X-ray crystallography and identified binding of two to P-pocket, which is composed of structural elements from polymerase active site, primer grip, and template-primer that are resilient to drugresistance mutations. Analogs of a fragment were synthesized of which two showed noticeable RT inhibition. An engineered RT/DNA aptamer complex trapped the transient P-pocket in solution. Structures of the RT/DNA complex were determined with a fragment and a synthesized analog bound at P-pocket by single-particle cryo-EM. Identification of P-pocket and the devised structurebased platform provide an opportunity for designing new types of polymerase inhibitors.

biophysics↗

bioRxiv2020

Cryo-EM structures reveal transcription initiation steps by yeast mitochondrial RNA polymerase

Cryo-EM structures of transcription pre-initiation complex (PIC) and initiation complex (IC) of yeast mitochondrial RNA polymerase show fully resolved transcription bubbles and explain promoter melting, template alignment, DNA scrunching, transition into elongation, and abortive synthesis. Promoter melting initiates in PIC with MTF1 trapping the -4 to -2 non-template (NT) bases in its NT-groove. Transition to IC is marked by a large-scale movement that aligns the template with RNA at the active site. RNA synthesis scrunches the NT strand into an NT-loop, which interacts with centrally positioned MTF1 C-tail. Steric clashes of the C-tail with RNA:DNA and NT-loop, and dynamic scrunching-unscrunching of DNA explain abortive synthesis and transition into elongation. Capturing the catalytically active IC-state with UTPS poised for incorporation enables modeling toxicity of antiviral nucleosides/nucleotides.

biophysics↗