From genetics to fruit growth: The crucial role of SlHAM4 in tomatoes
image: Tissue-specific expression of SlHAM4. (A–O) Histochemical staining for GUS activity in M82 (wild type) and transgenic tomato plants expressing GUS driven by SlHAM4 native promoter (SlHAM4pro::GUS). GUS activity was visualized using the chromogenic substrate X-Gluc after ethanol clearing. (A) Mature embryos extracted from seeds 1 DAI. (B–E) Representative whole seedlings at indicated DAG. Insets in B–D show isolated cotyledons (adaxial side). (F) Adaxial side of the first leaf distal half. (G) Seedling stem. Scale bars = 200 μm (A and F), 500 μm (B), 1 mm (C), 2 mm (D, E, and G). Inset scale bars = 500 μm (B and C), 1 mm (D). cot, cotyledon; hyp, hypocotyl. (J–O) Manual longitudinal (top panel) and cross (bottom panel) sections of anthesis ovary (J) and fruits at indicated developmental stage (K–N). DPA, days post-anthesis. Arrows indicate GUS staining in representative vasculature. Scale bars 1 mm (J–L), 1 cm (M–O). (H, I, O, and P) Histological cross-sections of the SlHAM4pro::GUS-8 tissues stained with Ruthenium red. (H) Seedling stem shown in (G). (O) Pericarp vasculature of mature green fruit shown in (M). Scale bar = 100 μm. (I and P) Higher magnification of the histological sections outlined in (H) and (O) by a black box. Scale bar = 20 μm. p, parenchyma; ph, phloem; pi, internal phloem; pe, external phloem; xy, xylem; se, sieve element cell; cc, companion cell.
Credit: Horticulture Research
Tomato development relies on intricate gene regulation, with one of the key genes, SlHAM4, emerging as a critical factor in shoot and fruit growth. In groundbreaking research, mutations in SlHAM4 led to significant abnormalities, including smaller fruits and catface-like scars. However, restoring the gene to its native state completely reversed these defects, underscoring its pivotal role in fruit development. The study reveals that SlHAM4 operates primarily within the phloem, vital for nutrient transport. By pinpointing how SlHAM4 regulates these processes, this research opens doors to enhancing crop growth and overcoming developmental disorders in tomatoes.
The HAIRY MERISTEM (HAM) gene family plays a crucial role in plant development, maintaining meristem activity and contributing to the formation of various plant structures. While the Type II members of this family have been extensively studied, the Type I genes like SlHAM4 in tomatoes were less understood. SlHAM4 is notably expressed in the phloem, a tissue essential for transporting nutrients. This research delves into how disruptions in SlHAM4 expression lead to developmental abnormalities, including smaller, scarred fruits. These findings suggest that SlHAM4’s role extends beyond simple structural maintenance, influencing complex processes vital to fruit formation.
In a study (DOI: 10.1093/hr/uhae325) published in Horticulture Research (March 2025), researchers investigated the SlHAM4 gene in tomatoes, revealing its significant role in both shoot and fruit development. By using CRISPR/Cas9 to induce mutations in SlHAM4, the team observed that the loss of function led to smaller, irregular fruits with catface-like scars. Reintroducing SlHAM4 reversed these phenotypes, proving the gene’s essential role. This research highlights SlHAM4’s involvement in phloem function, making it an important target for improving tomato fruit size and health.
The research provides new insights into the complex genetic mechanisms behind tomato growth. Mutations in the SlHAM4 gene resulted in distinct phenotypic changes: the mutants produced smaller fruits and exhibited catface-like scars, a developmental anomaly. Interestingly, these defects were reversed by reintroducing SlHAM4 under its native promoter, confirming that the observed abnormalities were directly linked to the loss of SlHAM4 function. Through transcriptomic analysis, the team discovered that the gene is primarily expressed in the phloem, crucial for the transportation of nutrients. This finding connects SlHAM4’s role to the regulation of key genes involved in phloem function.Furthermore, the study also identified a reduction in the expression of several genes essential for phloem function in the ovaries of mutant plants, pointing to SlHAM4’s regulatory influence on nutrient transport. Despite no structural abnormalities in the phloem itself, the reduced functionality of these cells in SlHAM4-deficient plants explains the observed fruit size reduction and scarring. This research provides a better understanding of how genetic factors influence the complex process of fruit development in tomatoes, with potential applications in crop improvement.
"SlHAM4 is more than just a gene for plant structure—it's a central player in regulating fruit development," said Dr. Tzahi Arazi, the senior author of the study. "Our findings show that SlHAM4’s expression in the phloem is crucial for proper nutrient transport, which directly affects fruit growth and quality. Understanding how SlHAM4 interacts with phloem-related genes opens up exciting possibilities for enhancing crop yields and preventing common fruit disorders like catfacing."
The discovery of SlHAM4’s role in tomato development has significant agricultural implications. By targeting this gene, researchers could potentially enhance fruit size, improve quality, and reduce defects such as catfacing. Additionally, the insights gained from this study could be applied to other crops, helping to optimize growth by enhancing phloem function. As phloem is essential for nutrient transport, understanding how SlHAM4 regulates this process could also improve stress resistance in plants. Future research could focus on utilizing this knowledge to develop genetically modified crops with better yield and fewer developmental disorders, benefiting both agriculture and food security.
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References
DOI
Original Source URL
https://doi.org/10.1093/hr/uhae325
Funding information
This work was supported by the ISF research grant 939/12 to T.A.
About Horticulture Research
Horticulture Research is an open access journal of Nanjing Agricultural University and ranked number one in the Horticulture category of the Journal Citation Reports ™ from Clarivate, 2023. The journal is committed to publishing original research articles, reviews, perspectives, comments, correspondence articles and letters to the editor related to all major horticultural plants and disciplines, including biotechnology, breeding, cellular and molecular biology, evolution, genetics, inter-species interactions, physiology, and the origination and domestication of crops.