Francesco Camerlengo

Background: Elevated soil temperatures, soil compaction and altered light conditions in connection with latitudinal changes are emerging environmental constraints in crop productivity. Because roots play a central role in water and nutrient acquisition, understanding the mechanisms underlying root developmental plasticity under these stresses is becoming essential for improving crop resilience. Scope: This review summarizes recent advances in the genetic, molecular and physiological mechanisms regulating root responses to increasing soil temperature, compaction and light. Roots respond to increasing temperature through thermomorphogenesis, which promotes adaptive growth under moderate warming, and heat-stress responses, which prioritize cellular protection under supra-optimal temperatures. The effects of soil compaction on roots result in morphological, anatomical, and growth dynamics changes including circumnutation. Climate change is expected to shift the optimal cultivation latitude of many crops, exposing them to changes in light intensity, spectral quality, and photoperiod that may result in yield penalties. Accordingly, responses to light are reviewed, both through direct root photoperception and systemic shoot-to-root signaling. Root adaptive responses to heat stress, soil compaction and altered light environments converge on interconnected regulatory networks involving auxin, HY5, PIFs, ethylene, YUCCA genes and PIN/AUX1 transporters, which integrate environmental signals to coordinate root developmental plasticity. Conclusion: Much of the current knowledge still derives from model species, while targeted studies in crops remain limited. Integrating high-throughput phenotyping, quantitative genetics, omics approaches, crop modelling and genome editing technologies will accelerate the identification and deployment of adaptive root traits to soil temperatures, soil compaction and altered light conditions for breeding climate-resilient crops.

Key message: Using genome-wide association analysis in a barley germplasm panel, we identified root trait QTLs, domestication-driven morphological shifts, and candidate genes to guide breeding for improved root ideotypes in modern cultivars. Root system architecture (RSA) determines the plant’s ability to anchor to soil and absorb water and nutrients, thereby affecting productivity and stress tolerance. In this study, we investigated phenotypic variation for seven root traits at the seedling stage, performed a genome-wide association study (GWAS), and identified novel quantitative trait loci (QTLs) and candidate genes using a germplasm collection representing global barley diversity. Traits heritability ranged from 0.70 to 0.88. Domestication and breeding syndromes were detected for seminal root number (SRN), which increased from 4.2 roots in wild accessions to 5.9 in landraces to 6.3 in modern cultivars. Similarly, root growth angle (RGA) widened from 42.9° in wild accessions to 60.3° in modern cultivars. Lateral root density and length increased from wild barley to cultivars, while average seminal root length (ARL) shortened. GWAS identified 106 QTLs explaining 25–61% of the phenotypic variation per trait. Candidate genes at GWAS peaks for SRN encoded ARABIDILLO - and WD-40 -related proteins, an exocyst complex component, and a serine protease; UDP-glycosyltransferase for RGA; and jasmonate receptor and F-box encoding genes for ARL. Our findings provide valuable insights for molecular biologists and breeders to design and implement root architecture ideotypes in new cultivars, enhancing their adaptability to challenging environments.

Parasitic weed infestations represent an increasing threat to agriculture worldwide, especially in the Mediterranean region. Phelipanche ramosa (L.) and P. aegyptiaca (Pers.) (broomrapes) cause severe yield losses in field-grown tomato (Solanum lycopersicum L.). Strigolactones (SLs) are apocarotenoid phytohormones that play a critical role in plant physiology and development but also act as the primary germination signals for parasitic weed seeds. In this study, we generated CRISPR/Cas9 tomato knock-out (KO) lines targeting the SlD27 gene and three other key genes involved in SL biosynthesis (SlCCD7, SlCCD8, SlMAX1), all in the same genetic background. All edited lines exhibited undetectable SL levels in root exudates, leading to a strong reduction in the in vitro germination of Phelipanche spp. seeds. Consistently, reduced parasitism was also observed in vivo when Sld27 lines were tested. A comprehensive evaluation of morphological, reproductive, and fruit-related traits revealed gene-specific phenotypic effects, including changes in vegetative growth, fruit set, fruit development, and volatilome. Specifically, knock-out of two CCDs and the SlMAX1 affected shoot architecture, fruit development, and the production of volatile organic compounds during fruit ripening. In contrast, the Sld27 lines, newly developed in this study, displayed a mild phenotype generally comparable to non-edited control plants and likely due to the expression of SlD27 paralogues. Overall, our results indicate that SlD27 represents a promising breeding target for enhancing resistance to parasitic weeds in tomato while minimizing negative impacts on plant development and fruit quality.

The plant cell wall is a crucial structure that ensures plant cell integrity and facilitates environmental adaptation. Cellulose is the primary component of the plant cell wall. Its biosynthesis is orchestrated through the plasma membrane-localized multiprotein cellulose synthase complex, which includes a membrane-anchored endo-1,4-ß-glucanase. Here, we identified a barley (Hordeum vulgare) mutant with short roots resulting from repressed cell division and elongation, which we designated H. vulgare endo-β-1,4-D-glucanase 3-1 (hvglu3-1). HvGLU3 encodes a putative membrane-anchored endo-1,4-ß-glucanase that is highly conserved across plant species. The hvglu3-1 mutant exhibited a 60% reduction in cellulose content, accompanied by changes in hemicellulose and suberin levels and an altered lignin structure in the roots. Subcellular localization analyses and bimolecular fluorescence complementation assays suggested a direct interaction between HvGLU3 and primary cellulose synthases. We investigated the reprogramming of the tissue-specific transcriptome in hvglu3-1 root tips using a combination of laser capture microdissection and RNA sequencing. This approach revealed that 74% of all genes that are actively expressed in the elongation zone are influenced by root cellulose biosynthesis. Gene coexpression analyses highlighted the essential role of cellulose biosynthesis in diverse biological processes, including cell wall organization, phytohormone signaling, and stress responses, to regulate root tissue development. Overall, our study demonstrates the partially conserved role of HvGLU3 in controlling cellulose biosynthesis in roots and provides valuable transcriptomic resources for future studies.

Root system architecture (RSA) determines the plant’s ability to anchor to soil and absorb water and nutrients, thereby affecting productivity and stress tolerance. In this study, we investigated phenotypic variation for seven root traits at the seedling stage, performed a genome wide association study (GWAS), and identified novel quantitative trait loci (QTLs) and candidate genes using a germplasm collection representing global barley diversity. Traits heritability ranged from 0.70 to 0.88. Domestication and breeding syndromes were detected for seminal root number (SRN), which increased from 4.2 roots in wild accessions to 5.9 in landraces to 6.3 in modern cultivars. Similarly, root growth angle (RGA) widened from 42.9° in wild accessions to 60.3° in modern cultivars. Lateral root density and length increased from wild barley to cultivars, while average seminal root length (ARL) shortened. GWAS identified 106 QTLs explaining 25% to 61% of the phenotypic variation per trait. Candidate genes at GWAS peaks included ARABIDILLO-related, WD-40-related, exocyst complex component, and serine-protease encoding genes for SRN; UDP-glycosyltransferase and pectate lyase for RGA; and jasmonate receptor and F-box encoding genes for ARL. Our findings provide valuable insights for molecular biologists and breeders to design and implement root architecture ideotypes in new cultivars, enhancing their adaptability to challenging environments.

Novel sources of genetic variability for water‐use efficiency (WUE) are needed in order to breed varieties more suitable to sustainable cropping systems. Here, a maize ( Zea mays L.) introgression library of the landrace Gaspé Flint into the reference line B73 was characterized in high‐throughput phenotyping platforms, both in well‐watered and moderate water‐deficit conditions, for water use, WUE, and root and shoot growth. Traits heritability ranged from 0.77 to 0.93. The introgression of Gaspé Flint chromosome segments into the B73 genome significantly altered several traits. Some introgression lines exhibited a faster shoot biomass accumulation than B73, resulting in higher WUE at the expense of root growth. Quantitative trait loci (QTL) mapping identified seven major QTL clusters affecting shoot growth and WUE, two of which overlapped, with opposite effects, with QTLs for root biomass known to include root developmental genes. These results support the non‐intuitive hypothesis that reduced root‐to‐shoot ratio positively affects maize WUE.

Parasitic weed infestations pose an increasing threat to agriculture worldwide, especially in the Mediterranean region. Phelipanche ramosa and P. aegyptiaca (broomrapes) cause severe damage to field-grown tomato ( Solanum lycopersicum L. ). Strigolactones (SLs), apocarotenoid phytohormones, play a critical role in plant physiology and development, and are also the primary signals that trigger the germination of parasitic weed seeds. We generated CRISPR/Cas9 tomato knock-out lines for the SlD27 gene, as well as three other key genes involved in SL biosynthesis ( SlCCD7 , SlCCD8 , SlMAX1 ), all within the same genetic background. The edited lines exhibited a marked reduction in SL content in root exudates, along with impaired broomrape seed germination. A comprehensive analysis of morphological, reproductive, and fruit-related traits revealed gene-specific effects on plant phenotype, including vegetative traits, fruit set, fruit development, and volatilome. Specifically, the knock-out of two CCDs and the MAX1 had a specific impact not only on plant development but also on the production of volatile organic compounds during fruit ripening. In contrast, the Sld27 lines, produced for the first time in this study, displayed a phenotype similar to the control non-edited plants, suggesting that the D27 gene holds promise as a breeding target for enhancing resistance to parasitic weeds in tomato. Highlight: The characterization of tomato CRISPR/Cas9-edited lines for the four core genes involved in strigolactone biosynthesis revealed gene-specific effects on plant phenotype, with D27 emerging as a potential target for resistance to parasitic weeds.