Cellular and molecular characterizations of a thick secondary cell wall somaclonal variant in Dendrocalamus farinosus

The development of the secondary cell wall (SCW) and cellulose synthesis are critical for the utility of bamboo in pulping. Dendrocalamus farinosus is one of the most versatile bamboo products. Somaclonal variation has been widely used to generate valuable genotypes and genes, thereby accelerating bamboo breeding. Herein, we generated a thick secondary cell wall variant (twv), via in vitro culture in D. farinosus. The twv variant exhibited a thicker SCW, larger diameter at breast height (DBH), wider vessel diameter, longer fiber length, and higher cellulose content compared to the wild type (WT). Transcriptomic and metabolomic analyses revealed 10168 differentially expressed genes (DEGs) and 3630 differentially accumulated metabolites (DEMs) between WT and twv, which were primarily enriched in carbon metabolism, starch and sucrose metabolism pathways. Compared to WT, the expression levels of DfMYB251, DfCesA4 and DfCesA7 were significantly upregulated in twv. The function of DfMYB251 was subsequently investigated. Sequence homology analysis showed that DfMYB251 was a homolog of AtMYB52, OsMYB41 and PtrMYB52. DfMYB251 was highly expressed in internodes and bamboo shoot. GUS activity driven by the DfMYB251 promoter (pDfMYB251::GUS) was predominantly detected in the stems and roots of transgenic plants. The DfMYB251 protein was localized to the nucleus. Furthermore, compared with WT, overexpression of DfMYB251 in Nicotiana tabacum resulted in transgenic plants with increased plant height, wider xylem, higher soluble sugar and cellulose contents, and enhanced salt tolerance. Under salt stress, the salt-responsive gene NtERD10C was significantly upregulated in the transgenic lines. Taken together, these findings enhance our understanding of the multifunctional roles of DfMYB251 and provide novel insights into the genetic improvement of D. farinosus and other economic crops.