Brassinosteroids (BR) play important roles in plant growth and development. Although BR receptors have been intensively studied in Arabidopsis, the BR receptors in soybean remain largely unknown. Here, in addition to the known receptor gene Glyma06g15270 (GmBRI1a), we identified five putative BR receptor genes in the soybean genome: GmBRI1b, GmBRL1a, GmBRL1b, GmBRL2a, and GmBRL2b. Analysis of their expression patterns by quantitative real-time PCR showed that they are ubiquitously expressed in primary roots, lateral roots, stems, leaves, and hypocotyls. We used rapid amplification of cDNA ends (RACE) to clone GmBRI1b (Glyma04g39160), and found that the predicted amino acid sequence of GmBRI1b showed high similarity to those of AtBRI1 and pea PsBRI1. Structural modeling of the ectodomain also demonstrated similarities between the BR receptors of soybean and Arabidopsis. GFP-fusion experiments verified that GmBRI1b localizes to the cell membrane. We also explored GmBRI1b function in Arabidopsis through complementation experiments. Ectopic over-expression of GmBRI1b in Arabidopsis BR receptor loss-of-function mutant (bri1-5 bak1-1D) restored hypocotyl growth in etiolated seedlings; increased the growth of stems, leaves, and siliques in light; and rescued the developmental defects in leaves of the bri1-6 mutant, and complemented the responses of BR biosynthesis-related genes in the bri1-5 bak1-D mutant grown in light. Bioinformatics analysis demonstrated that the six BR receptor genes in soybean resulted from three gene duplication events during evolution. Phylogenetic analysis classified the BR receptors in dicots and monocots into three subclades. Estimation of the synonymous (K_s) and the nonsynonymous substitution rate (K_a) and selection pressure (K_a/K_s) revealed that the K_a/K_s of BR receptor genes from dicots and monocots were less than 1.0, indicating that BR receptor genes in plants experienced purifying selection during evolution.

To overcome rubber tree (RT) tissue culture explant source limitations, the current study aimed to establish a new Hevea brasiliensis somatic embryogenesis (SE) system, laying the technical foundation for the establishment of an axillary-bud-based seedling regeneration system. In this study, in vitro plantlets of Hevea brasiliensis Chinese Academy of Tropical Agricultural Sciences 917 (CATAS 917) were used as the experimental materials. Firstly, the optimum conditions for axillary bud swelling were studied; then, the effects of phenology, the swelling time of axillary buds (ABs), and medium of embryogenic callus induction were studied. Plantlets were obtained through somatic embryogenesis. Flow cytometry, inter-simple sequence repeat (ISSR molecular marker) and chromosome karyotype analysis were used to study the genetic stability of regenerated plants along with budding seedlings (BSs) and secondary somatic embryo seedlings (SSESs) as the control. The results show that the rubber tree’s phenology period was mature, and the axillary bud induction rate was the highest in the 2 mg/L 6-benzyladenine (6-BA) medium (up to 85.83%). Later, 3-day-old swelling axillary buds were used as explants for callogenesis and somatic embryogenesis. The callus induction rate was optimum in MH (Medium in Hevea) + 1.5 mg/L 2,4-dichlorophenoxyacetic acid (2,4-D) + 1.5 mg/L 1-naphthalene acetic acid (NAA) + 1.5 mg/L Kinetin (KT) + 70 g/L sucrose (56.55%). The regenerated plants were obtained after the 175-day culture of explants through callus induction, embryogenic callus induction, somatic embryo development, and plant regeneration. Compared with the secondary somatic embryo seedling control, axillary bud regeneration plants (ABRPs) were normal diploid plants at the cellular and molecular level, with a variation rate of 7.74%.

Anther-derived somatic embryogenesis is a valuable approach in rubber tree (Hevea brasiliensis) breeding; however, its effectiveness is highly influenced by the developmental stage of the microspores. The present investigation focused on male flower buds of the cultivar Reyan 73397 at successive developmental stages to examine the relationship between visible bud characteristics and internal microspore development, assess how microspore developmental stage affects callus induction and somatic embryo formation, and identify the stage with the greatest embryogenic potential. Cytological observations distinguished six well-defined phases of microspore development, spanning from microspore mother cells to fully mature pollen grains, each reliably linked to particular bud diameters, coloration, and anther morphology. Anthers corresponding to each developmental phase were cultured in vitro, and their ability to initiate callus and produce somatic embryos was systematically evaluated. Anthers containing uninucleate microspores exhibited the highest rates of both callus formation and somatic embryogenesis, with the early-uninucleate stage showing the strongest response. This stage consistently matched flower buds measuring 1.42–1.57 mm in transverse diameter and displaying a green to yellowish-green appearance. In contrast, anthers collected at the microspore mother cell and tetrad stages did not produce embryogenic responses. Histological evidence has indicated that both callus and somatic embryos originate from diploid somatic tissues of the anther wall, particularly connective parenchyma cells, rather than from microspores themselves. Based on these findings, a rapid, non-destructive selection method integrating bud diameter, bud color, and sieve-based size separation was developed to identify responsive explants efficiently. Overall, this study defines the optimal developmental window for anther culture in rubber trees, verifies the somatic origin of embryogenic tissues, and provides a practical morphological and cytological basis for improving anther culture efficiency in rubber tree breeding programs.