On July 2, 2025, Researcher Xie Qi’s team at the Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, published an online article in Molecular Plant titled “Vascular tissue-specific expression of an endo-1,4-β-xylanase enhances forage efficacy of sweet sorghum silage” (Impact Factor: 24.1).
To investigate the phenomenon “even under adequate soil moisture, the M19 mutant still displays drought‐like symptoms”, the plants were moved into Jiupo plant growth chambers for hydroponic culture, and the accumulation of rhodamine B in leaves was measured.
This study elucidated the function of a sorghum xylanase gene. Using a vascular‐tissue specific complementation strategy, the team successfully resolved the breeding challenge that forage digestibility negatively correlates with biomass in sweet sorghum xylanase mutants, providing a new approach for efficient utilization of lignocellulosic biomass in energy crops.
The research team screened an EMS‐mutagenized mutant library of sweet sorghum (line E048) and identified a mutant named M19. This mutant displayed abnormally soft leaves, but also showed undesirable phenotypes such as reduced plant height and lowered biomass. Using MutMap+ analysis combined with gene editing validation, the team identified a GH10 family xylanase gene, SbXyl, as the causal gene. In the mutant, a point mutation from cytosine to thymine caused a premature stop codon, disrupting the GH10 domain and rendering the enzyme unable to hydrolyze its substrate, xylan.
Expression pattern analysis revealed that SbXyl is highly expressed in stem internodes during developmental stages; loss of function induced dual effects: on the one hand, it impaired vascular tissue development, resulting in reduced vascular bundle area and thinner secondary cell walls in fiber cells, which hindered water transport and caused developmental defects; on the other hand, it altered cell wall composition and structure, improving forage quality in the mutant. In vitro rumen digestion assays showed that, before ensiling, the digestibility of mutant plants increased by 14.7% compared to wild-type; after ensiling, the digestibility remained 7.7% higher than wild-type. However, growth and developmental defects limit the mutant’s practical application.
Figure. Improved forage digestibility exhibited by xylanase gene mutants
To overcome the negative correlation between forage quality and biomass, the research team developed a vascular tissue‐specific complementation strategy. By homologous gene comparison and a GUS reporter system, they identified SbNAC31, a sorghum gene with vascular tissue‐specific expression. They used the promoter of SbNAC31 to drive SbXyl expression in the mutant background, generating VSC transgenic lines. Phenotypic observations and measurements showed that these VSC lines successfully rescued the growth defects of the mutant: water transport capacity and biomass were restored to wild‐type levels. Notably, the VSC lines retained the superior forage quality of the mutant: pre-ensiling digestibility of wild‐type plants was 47.72%, while that of different VSC lines was 51.27%–54.03%, representing an increase of 7.5–13.2% over wild‐type; post-ensiling, wild-type digestibility was 51.08%, and VSC lines achieved 54.81%–55.12%, still showing a 7.3–7.9% advantage.
Figure. VSC materials restored mutant growth and development without compromising enhanced forage quality
In summary, this study elucidated the role of the sorghum xylanase gene SbXyl in secondary wall deposition and vascular tissue development. Using a vascular tissue‐specific complementation strategy, the researchers engineered the xylanase mutant to be usable: they restored biomass yield while retaining improved forage digestibility. This lays a foundation for efficient utilization of lignocellulosic biomass in energy crops.
Author Information
The first authors are Dr. Ge Fengyong (postdoctoral fellow) and former PhD student Wei Huimin, both at the Institute of Genetics and Developmental Biology, Chinese Academy of Sciences. The corresponding author is Researcher Xie Qi (same institute). Other significant contributors include Researchers Zhou Yihua and Zhang Baocai (IGDB, CAS); Professors Yu Feifei and Yang Fuyu (China Agricultural University); Researchers Zhong Jin and Associate Researcher Teng Kunling (Institute of Microbiology, CAS). The research was supported by the National Key R&D Program and the National Natural Science Foundation of China, among other funding sources.