Peanut is a significant economic and oilseed crop worldwide, playing a crucial role in meeting the demand for high-quality edible oil and protein. Increasing peanut yield and mechanized production are key objectives in peanut breeding. Peanuts are nutritionally rich, with a kernel fat content of approximately 50%, protein content of around 25%, and sugar content of about 10% (Pandey et al., 2012; Arya et al., 2016). Additionally, they contain various beneficial ingredients such as vitamins, minerals, essential amino acids, and unsaturated fatty acids (Kayam et al., 2017). Widely cultivated across continents like Asia, Africa, and the Americas, peanuts have an annual production of roughly 35.5 million tons. China holds a dominant position in the global peanut industry, serving as a significant production and consumption center and ranking among the world’s leaders in planting scale and yield (Gallavotti, 2013).

For crop yield, plant type plays a crucial role. Plant type encompasses the spatial morphology and distribution characteristics of roots, stems, leaves, branches, and flowers. In 1968, Donald introduced the concept of ‘idotype’ to describe the ‘ideal plant type’ for crops, emphasizing low competition among individuals and maximum biomass accumulation in grains (Donald, 1968). He suggested that the ideal wheat plant type should have an upright and short stem, a large spike, awns, and short leaves. This ideal plant type can significantly boost crop yield, with lateral branches being a key component that influences yield. Peanuts’ lateral branches originate from axillary buds on the main stem, drawing nutrients from it (Wang et al., 2018; Ward and Leyser, 2004). Effective branches, capable of bearing pods, are distinguished from ineffective branches. Peanut plant types are categorized into upright, semi spreading type and spreading type based on the angles of lateral branches and the ratio of the first pair’s length to the main stem’s height (plant type index) (Hammons et al., 2016). Creeping lateral branches, which grow close to the ground with slightly raised tops and a plant type index of about 2 or more, fall into the creeping type. The lateral branches of half-erection plants bend upwards from the base, while the upper part grows upright, with the upright part being greater in length than the curved part, resulting in a plant type index of approximately 1.5. On the other hand, the lateral branches of upright plants also bend upwards from the base, with the angle between the first pair of lateral branches and the main stem being less than 45°, leading to a plant type index of about 1.1-1.2. The main peanut varieties currently promoted in China are upright, featuring compact plants with pods primarily concentrated at the bottom, making them suitable for high-density cultivation and economically viable for small-scale farmers (Chen et al., 2016). The completion of genome sequencing in cultivated peanuts has ushered in a new era of functional genomics research, particularly in the realm of peanut plant types (Chen et al., 2019; Zhuang et al., 2019; Bertioli et al., 2019). Research utilizing SSR and transposon markers has led to the construction of a genetic map, identifying two major QTLs controlling branching angle on 2 linkage groups (Shirasawa et al., 2012). Another study pinpointed the collateral angle in a 4.08 Mb interval at the end of chromosome B05 using the RIL population (Li et al., 2019a). Furthermore, through the use of synthetic tetraploid and fleur11 to create chromosome fragment replacement lines and BSA analysis, researchers successfully mapped the genes governing the relative traits of lateral spreading and erect growth to the end of A08 linkage group and B05 chromosome, with the candidate gene being bunch1 (Fonceka et al., 2012).

Erect type peanuts have some drawbacks as the early flowers on the base of lateral branches are close to the ground, allowing pegs to form pods, while the later flowers higher up cannot. In comparison, semi spreading type and spreading type peanuts can conserve seed usage due to wider lateral branch angles and increased coverage (Zhou et al., 2016). Their lower lateral branches enable pegs to efficiently enter the soil, boosting per plant yield and facilitating mechanized harvesting. Additionally, post-harvest, they can be easily air-dried on site, reducing the risk of Aspergillus flavus contamination. The lateral branch angle of peanuts plays a vital role in yield, disease resistance, and mechanized harvesting, yet the genetic and molecular mechanisms behind this trait remain unclear.

The offspring plants produced by backcrossing PZ42 and Jihua 5 undergo recombination within the QTL interval. Reduce QTL interval through fine mapping and identify major genes related to peanut lateral branch angle. This study aims to uncover the genetics of peanut lateral branch angle and identify potential key genes, ultimately advancing molecular breeding and enhancing peanut germplasm resources.

Multiple studies have shown that the angle of branching is determined by the uneven distribution of auxin, which is influenced by gravity and light. This distribution is affected by auxin synthesis, transport, and signal transduction, which in turn lead to asymmetric growth induced by auxin. When it comes to gravity sensing, the amyloplasts in stems can sense gravitational cues and move accordingly, playing a pivotal role in this process (Sack, 1997). Additionally, research on rice stems has revealed that the AGPL1 and agpl1agpl3 double mutants inhibit starch synthesis, resulting in a decreased gravitropic response and an increased tiller angle (Okamura et al., 2013, 2014). Furthermore, genes such as SGR, SGR2, SGR3, SGR4, SGR5, SGR6, and SGR9 in Arabidopsis are involved in regulating the deposition of amyloplasts, thereby influencing the gravity response (Hashiguchi et al., 2013; Nakamura et al., 2011; Tanimoto et al., 2008). In rice, the LPA1 gene, which is a counterpart to the SGR5 gene, controls the sedimentation rate of amyloplasts to impact the plant’s gravitropic response. Moreover, in collaboration with the transcription factor ONAC106, it also affects the tiller angle (Morita et al., 2006; Wu et al., 2013; Sakuraba et al., 2015).

Studies have shown that Strigolactone (SL) can decrease the tiller angle by inhibiting auxin biosynthesis (Sang et al., 2014). The Prog1 (Promote Growth 1) gene is responsible for promoting ground growth in rice, with mutations causing the plant to grow upright (Jin et al., 2008; Tan et al., 2008; Hu et al., 2018). Research on rice has found that LAZY1 and LAZY4 regulate the gravity and tiller angle of branches, leading to lateral auxin transport under gravity stimulation and changes in tiller angle caused by uneven redistribution of auxin (Wang et al., 2024; Li et al., 2019b). African cultivated rice and Asian cultivated rice exhibit creeping and erect growth types, respectively, with deletions of approximately 110 Kb and 113 Kb in their prog1 gene. Additionally, within this region, there are seven tandem zinc finger protein genes that may play a role in regulating tiller angle (Wu et al., 2018).

The research indicates that plants exhibit phototropic growth, with branches bending towards light due to the uneven distribution of auxin. Similar to gravitropism, phototropism involves light signal perception, transduction, auxin distribution, and organ curvature. Throughout plant development, a shade avoidance response ensures that plant branches and leaves grow upwards to maximize sunlight exposure (Roychoudhry et al., 2017; Ballaré et al., 1990). Research has demonstrated that in shaded conditions, such as with corn, phytochrome-mediated signals trigger an increase in tb1 expression, leading to branch inhibition. This response is also observed in sorghum and Arabidopsis (Kebrom et al., 2006; Whipple et al., 2011; Yasuko et al., 2014; Xie et al., 2020).

Waite demonstrated that the TAC1 (Tiller Angle Control 1) gene is light-dependent and responsive to light signals for regulating lateral branch angles (Waite and Dardick, 2018). In dark conditions, the core inhibitor of the light signal transduction pathway, COP1, inhibits TAC1 expression in Arabidopsis thaliana, leading to reduced branch angles. Studies in rice by have shown that higher TAC1 expression correlates with larger tiller angles (Li et al., 2007). Similarly, in maize, mutations in the TAC1 gene result in smaller leaf angles and a more compact plant structure, as described by (Ku et al., 2011). These findings indicate a conserved role of TAC1 in controlling branch and leaf angles in different plant species, including Arabidopsis.

In the research of peanut plant morphology three genes related to hormone metabolism were identified: one encoding ‘F-box protein’, another encoding 2-oxoglutarate, and the third encoding ‘Fe(II)-dependent oxygenase’. The research also revealed notable variations in cytokinin, auxin, and ethylene levels at the junction of the main stem and lateral branches between prostrate and upright peanuts (Pan et al., 2022). Through transcriptome data analysis, Ahmad identified 13 genes associated with gravity response, 22 genes linked to plant hormones, and 55 transcription factors. Additionally, he conducted a preliminary analysis of the metabolic pathways related to peanut lateral branch angles ( Figure 6 ) (Ahmad et al., 2022).

Research on the lateral branch angle of peanuts is currently less advanced compared to crops like rice and wheat. To develop high-yielding peanut varieties suitable for mechanized harvesting, it is crucial to delve deeper into gene mechanisms, enhance metabolic pathway regulation, and accelerate the breeding process. Additionally, the development of specialized machinery for peanuts can help reduce labor costs and enhance overall efficiency.

In this study, the secondary population constructed by the hybrid progeny PZ42 and Jihua 5 was used to fine map the lateral branch angle of peanut, and the QTL interval length was reduced from 4.08Mb to 48kb. The genes in the fine-mapping interval were screened, that the Aralbab05 gene encoding F-BOX protein was identified as a candidate gene related to the lateral branch angle of peanut, which was quantitatively verified in Jihua 5 and M130 in real-time. The real-time quantitative results showed that when the lateral branches of peanut were 1-10 cm, the expression of Aralbab05 in Jihua 5 was higher than that in M130.