Disruption of Zea mays isochorismate synthase1 decreases PHENYLALANINE AMMONIA LYASE activity and suppresses hypersensitive response-induced metabolism

Benke, R. L.; McCoy, R. M.; Ibrahim, I. M.; Simpson, J. P.; Muro-Villanueva, F.; Zhan, R. R.; Chapple, C.; Widhalm, J. R.; Puthiyaveetil, S.; Johal, G. S.; Dilkes, B. P.

doi:10.1101/2022.11.04.515247

bioRxiv · 10.1101/2022.11.04.515247

Disruption of Zea mays isochorismate synthase1 decreases PHENYLALANINE AMMONIA LYASE activity and suppresses hypersensitive response-induced metabolism

Benke, R. L.·McCoy, R. M.·Ibrahim, I. M.·Simpson, J. P.·Muro-Villanueva, F.·Zhan, R. R.·Chapple, C.·Widhalm, J. R.·Puthiyaveetil, S.·Johal, G. S.·Dilkes, B. P.

View original source ↗Export metadata ↓

Abstract

ISOCHORISMATE SYNTHASE (ICS) catalyzes the isomerization of chorismate to isochorismate, an essential precursor in the biosynthesis of the Photosystem I electron carrier phylloquinone and of one of two pathways for the biosynthesis of the defense response hormone salicylic acid (SA). We characterized a Zea mays ics1 mutant for impacts on metabolism, photosynthesis, and immune signaling. Phylloquinone was reduced in the mutant resulting in low electron transfer rates and high electron backflow rates. SA accumulation induced by autoactive alleles of the nucleotide-binding leucine-rich repeat (NLR) gene Resistance to Puccinia sorgi1 (Rp1) required ics1. Induced accumulation of SA was not required for lesion formation by the autoactive Rp1-D21#4 allele. Metabolomic analyses and SA supplementation of Rp1-D21#4 mutants, ics1-1 mutants and Rp1-D21#4; ics1-1 double mutants demonstrated that most hypersensitive response-induced metabolism required ics1 but this was independent of SA accumulation. Both the PAL and ICS pathways contributed to SA biosynthesis in maize as labeled phenylalanine was incorporated into SA glucoside. Maize ics1-1 mutants had low PHENYLALANINE AMMONIA LYASE activity, accumulated phenylalanine, and decreased abundance of phenylalanine derived metabolites. This demonstrates that the ICS and PAL pathways interact by a yet unknown mechanism complicating the interpretation of SA biosynthesis in plants from genetics alone.

Explore related subjects

plant biology Preprint

Keep this discovery

Explore connections, maps & timelines

BibTeX RIS

Benke, R. L., McCoy, R. M., Ibrahim, I. M., Simpson, J. P., Muro-Villanueva, F., Zhan, R. R., Chapple, C., Widhalm, J. R., Puthiyaveetil, S., Johal, G. S., Dilkes, B. P.. 2022-11-05. Disruption of Zea mays isochorismate synthase1 decreases PHENYLALANINE AMMONIA LYASE activity and suppresses hypersensitive response-induced metabolism. https://doi.org/10.1101/2022.11.04.515247

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related preprints

bioRxiv2026

Analysis of SpCas9 on- and off-target effects in high efficiency multiplex editing in Arabidopsis

RNA-guided nucleases (RGNs), such as Cas9 from Streptococcus pyogenes (SpCas9), are widely used for plant genome editing. Previous surveys for off-targeting, the modification of unintended targets with similarity to the intended target, indicate high specificity of SpCas9 in plant cells. However, off-targeting has not been assessed for efficiency-optimized editing systems combined with extensive multiplexing, which might increase the likelihood of cleavage at unintended sites. We therefore analyzed Arabidopsis thaliana lines that had been extensively mutagenized using zCas9i and up to 29 gRNAs addressing >45 target sites over several rounds of editing. Genomes were sequenced by short- and long-read technologies, and genome-wide variants were catalogued. Our pipeline for variant calling reliably detected RGN-induced mutations at on-targets. When excluding these on-target modifications, variants were detected in edited lines at frequencies similar to those previously reported for spontaneous mutations. In further analyses, we did not find any evidence for an origin of these variants from RGN activity. Our data are thus consistent with high specificity of SpCas9. In contrast, we detected genomic reorganization events upon editing at two complex loci, RPP1 and RPP7, encompassing multiple homologous genes, and also identified an allele by WGS that had escaped detection by amplicon sequencing. We conclude that, while off-targets may efficiently be avoided by selection of specific gRNAs, on-target modifications may be more extensive than intended, especially at complex loci and/or during multiplexing.

plant biology↗

bioRxiv2026

Seeding paradise: germination ecophysiology of Xyris paradisiaca Wand. (Xyridaceae), an endangered endemic species from Central Brazil

Seed ecophysiology is essential for understanding plant regeneration and developing effective conservation and ecological restoration strategies, yet knowledge remains scarce for most threatened Cerrado species. We characterised the germination niche, desiccation tolerance and storage behaviour of Xyris paradisiaca (Xyridaceae), an Endangered species endemic to Central Brazil, to assess whether its restricted distribution is associated with narrow germination requirements and to inform seed-based conservation. Germination was tested across light regimes, constant temperatures, decreasing water potentials and short-duration heat shocks, while thermal- and hydro-time models were used to quantify thermal and hydric thresholds. Seeds exhibited an absolute light requirement but broad abiotic tolerances. Germination remained >87% between 15 and 40 {degrees}C, with estimated cardinal temperatures of Tb = 8.94 {degrees}C, To = 33.13 {degrees}C and Tc = 45.53 {degrees}C. Germination remained similar to the control down to -0.6 MPa and exceeded 40% at -1.0 MPa, with a median base water potential of {Psi}b = -1.03 MPa. Germination also remained high after 1-min heat shocks up to 200 {degrees}C. Seeds were desiccation tolerant, with 100% germination after drying and a viability loss index of -0.04, and germination remained >90% after 24 months of ambient storage. Thus, the highly restricted distribution of X. paradisiaca is not driven by a narrow physiological germination niche. Its broad environmental tolerances, desiccation tolerance and favourable storage behaviour also highlight its unexplored potential for seed-based restoration, propagation and ex situ conservation.

plant biology↗

bioRxiv2026

Planted origin of shade trees: a robust determinant of cocoa yield among smallholder farmers in Cote d'Ivoire

CONTEXT: While the agroeconomic literature on the determinants of cocoa yield among West African smallholders is abundant, it remains dominated by descriptive studies or work conducted at an aggregated regional scale, leaving open the question of the role of shade-tree management practices at the scale of the individual plantation. OBJECTIVE: This study tests whether shade-tree management practices and the farmer's socio-demographic profile explain variation in cocoa yield, using a nationwide sample of 409 plantations covering, for the first time, the three major Ivorian production zones (loops) (98, 151 and 160 plantations for loops 1, 2 and 3, respectively). METHODS: A univariate screening of 27 variables, a mixed model with a random intercept by village, a production-function specification, LASSO variable selection, and a random forest were applied, all evaluated by 5-fold cross-validation. RESULTS AND CONCLUSIONS: The five approaches converge on a robust result: the deliberately planted origin of shade trees (as opposed to a residual or spontaneous origin) is the strongest and most stable determinant of yield, with a mean gap of 332 versus 183 kg/ha/year. This effect withstands four successive robustness checks: it remains significant after simultaneous adjustment for age, plantation size, production zone, technical extension, and farmer education; it is not driven by a handful of extreme plantations; it holds within each of the three production zones taken separately rather than in only one of them; and, taken in isolation, it retains a positive out-of-sample predictive power (cross-validated R2=8776; 0.05). A second group of robust determinants of more modest magnitude emerges for agricultural technical extension (ANADER/CNRA/SATMACI) and farmer education level; shade-tree alignment shows a signal in the same direction, consistent with recent independent work in Cote d'Ivoire, but becomes statistically marginal once adjusted for these other factors. The full multivariate model reaches a cross-validated R2 of around 0.07-0.08. SIGNIFICANCE: This signal, undetectable in an analysis restricted to loop 1 alone (n=98) for lack of statistical power, confirms the value of nationwide sampling for detecting modest but real agronomic determinants, and argues for integrating shade-tree origin into agroforestry extension programmes.

plant biology↗