Adaptation mechanism of three Impatiens species to different habitats based on stem morphology, lignin and MYB4 gene

Abstract

Background: Impatiens is an important genus with rich species of garden plants, and its distribution is extremely extensive, which is reflected in its diverse ecological environment. However, the specific mechanisms of Impatiens' adaptation to various environments and the mechanism related to lignin remain unclear.

Results: Three representative Impatiens species,Impatiens chlorosepala (wet, low degree of lignification), Impatiens uliginosa (aquatic, moderate degree of lignification) and Impatiens rubrostriata (terrestrial, high degree of lignification), were selected and analyzed for their anatomical structures, lignin content and composition, and lignin-related gene expression. There are significant differences in anatomical parameters among the stems of three Impatiens species, and the anatomical structure is consistent with the determination results of lignin content. Furthermore, the thickness of the xylem and cell walls, as well as the ratio of cell wall thickness to stem diameter have a strong correlation with lignin content. The anatomical structure and degree of lignification in Impatiens can be attributed to the plant's growth environment, morphology, and growth rate. Our analysis of lignin-related genes revealed a negative correlation between the MYB4 gene and lignin content. The MYB4 gene may control the lignin synthesis in Impatiens by controlling the structural genes involved in the lignin synthesis pathway, such as HCT, C3H, and COMT. Nonetheless, the regulation pathway differs between species of Impatiens.

Conclusions: This study demonstrated consistency between the stem anatomy of Impatiens and the results obtained from lignin content and composition analyses. It is speculated that MYB4 negatively regulates the lignin synthesis in the stems of three Impatiens species by regulating the expression of structural genes, and its regulation mechanism appears to vary across different Impatiens species. This study analyses the variations among different Impatiens plants in diverse habitats, and can guide further molecular investigations of lignin biosynthesis in Impatiens.

Keywords: Impatiens; MYB4 gene; Expression analysis; Lignin; Stem morphological anatomy.

Fig. 1

Test materials. A: I. chlorosepala. B: I. uliginosa.C: I. rubrostriata

Fig. 2

Transverse (A, B, D, E, G, H) and longitudinal (C, F, I) light microscope stem sections of Impatiens species. A and B Transverse section of I. chlorosepala. C Tangential section of I. chlorosepala. D and E Transverse section of I. uliginosa. F Tangential section of I. uliginosa. G and H Transverse section of I. rubrostriata. I Tangential section of I. rubrostriata. Ep: epidermal cells, Co: cortex, Pa: parenchyma cells, Vb: vascular bundle, Ve: vessels, Vc: cambium, Mr: medullary ray, Xyl: xylem, Pi: pith, Ph: phloem

Fig. 3

Phylogenetic tree of MYB4 of three Impatiens species (NJ)

Fig. 4

The expression pattern of MYB4 in different parts of three Impatiens species. A The expression pattern of MYB4 in different parts of I. chlorosepala. B The expression pattern of MYB4 in different parts of I. uliginosa. C The expression pattern of MYB4 in different parts of I. rubrostriata. D Relative expression of MYB4 gene in the stems of three Impatiens species. Different lowercase letters indicate significant differences (P < 0.05)

Fig. 5

Relative expression of structural genes in the stems of three Impatiens species. Different lowercase letters indicate significant differences (P < 0.05)