Ao et al. identified a BPM domain-containing gene on chromosome 10 as a key regulator of panicle exsertion in sorghum, linking impaired BR signaling and reduced parenchyma cell elongation to a sheathed panicle phenotype, with implications for breeding varieties suited for mechanized harvesting.

Sorghum (Sorghum bicolor), the fifth most cultivated cereal globally, is a C4 plant with superior photosynthetic efficiency, stress tolerance, and adaptability to arid environments. Panicle exsertion (PE)—the elongation of the uppermost internode—is critical for grain yield, pollination efficiency, and mechanized harvesting. In this study, scientists from Guizhou University and Guizhou Academy of Agricultural Sciences identified a sheathed panicle (shp-I) mutant with significantly shortened PE from an EMS-mutagenized population of the variety Hongyingzi (HYZ). Compared to wild-type plants, the mutant displayed reduced plant height, grain size, and internode elongation, primarily due to impaired elongation of parenchyma cells. Histological analysis confirmed decreased cell length and width, similar to defects observed in rice PE mutants such as sui2 and OsWRKY78, highlighting the conserved role of parenchyma extensibility in grass internode development.

Further analysis revealed that brassinosteroids (BR) and auxin (IAA) play central roles in regulating PE elongation. Although gibberellin (GA3) levels were unchanged in the mutant, BR concentration was elevated, likely due to disrupted BR signaling, triggering feedback upregulation of BR biosynthesis. This BR overaccumulation appears to suppress auxin levels, impairing cell elongation. Genetic mapping localized the causal locus to chromosome 10, overlapping with previously reported QTLs. A candidate gene, SbiHYZ.10G230700, encoding a BPM domain-containing protein—a component of the E3 ubiquitin ligase complex—was identified. Mutations within its MATH domain may impair substrate recognition, disrupting BR signaling and PE development. This discovery provides valuable insights into sorghum internode elongation and offers a molecular target for breeding varieties suited for efficient mechanical harvesting.

SorghumBase examples: 

Figure 1 a: The author identified the gene SbiHYZ.10G230700 on Sorghum bicolor (L.) Moench variety Hongyingzi (HYZ) to be the candidate gene responsible for the sheathed panicle-I (shp-I) mutant phenotype. However this sorghum genome is not included in sorghumbase yet. In order to identify its ortholog in the reference sorghum BTx623, we started out by identifying the rice orthologous gene LOC_Os08g13030, reported in this paper. Furthermore, the rice orthologous gene LOC_Os08g13030 seems to be a MSU name, not the standard gene name used in the sorghumbase outgroup rice genome. To identify the standard rice gene name, we went to GrameneOryza and searched with this MSU name and found the IRGSPv1 rice gene name to be Os08g0226800. Consistent with the description from the paper, it encodes a BTB/POZ and MATH (BPM) domain protein.
Figure 1b: the ortholog link brings us to the BTx623 ortholog SORBI_3007G080600.
Figure 2 a: the reference expression view shows that this gene is highly expressed in sorghum reproductive tissues. It also has many paralogs.
Figure 2 b: the BAR expression view indicates that this gene (SORBI_3007G080600) is expressed in root, leaf, flag leaf, sheath, peduncle, internode, panicle and seeds, consistent with the paper’s finding in Sb.HYZ.
Figure 3: the neighborhood conservation view of SORBI_3007G080600 confirms that this gene has many paralogs across the sorghum clade. For BTx623, six copies are present in the vicinity of SORBI_3007G080600 in both directions and orientations. The structure variations across the different sorghum genomes are prominent, indicating potential ongoing selection of the region.
Figure 4 a: the variation view of this gene (SORBI_3007G080600) lays out known genetic variations with various consequences including amino acid changes, protein truncations, frameshifts …
Figure 4 b: the germplasm tab lists the sorghum lines harboring these mutations and point users to the germplasm centers to obtain the seeds for experiments.

Reference:

Ao J, Wang R, Li W, Ding Y, Xu J, Cao N, Gao X, Cheng B, Zhao D, Zhang L. Gene mapping and candidate gene analysis of a sorghum sheathed panicle-I mutant. Plant Genome. 2025 Mar;18(1):e70007. PMID: 40032606. doi: 10.1002/tpg2.70007. Read more

Identification of a BPM Domain-Containing Gene Regulating Panicle Exsertion in Sorghum for Mechanized Harvesting Adaptation

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