Abstract
In vascular plants, the importance of R2R3-myeloblastosis (R2R3-MYB) transcription factors (TFs) in the formation of secondary cell walls (SCWs) has long been a controversial topic due to the lack of empirical evidence of an association between TFs and downstream target genes. Here, we found that the transcription factor PmMYB7, which belongs to the R2R3-MYB subfamily, is involved in lignin biosynthesis in Pinus massoniana. PmMYB7 was highly expressed in lignified tissues and upon abiotic stress. As a bait carrier, the PmMYB7 protein had no toxicity or autoactivation in the nucleus. Forty-seven proteins were screened from the P. massoniana yeast library. These proteins were predicted to be mainly involved in resistance, abiotic stress, cell wall biosynthesis, and cell development. We found that the PmMYB7 protein interacted with caffeoyl CoA 3-O-methyltransferase-2 (PmCCoAOMT2)—which is involved in lignin biosynthesis—but not with beta-1, 2-xylosyltransferase (PmXYXT1) yeast two-hybrid (Y2H) studies. Our in vivo coimmunoprecipitation (Co-IP) assay further showed that the PmMYB7 and PmCCoAOMT2 proteins could interact. Therefore, we concluded that PmMYB7 is an upstream TF that can interact with PmCCoAOMT2 in plant cells. These findings lay a foundation for further research on the function of PmMYB7, lignin biosynthesis and molecular breeding in P. massoniana.
Highlights
IntroductionThe complex structure of the plant cell wall differs among different species and tissue types
Accepted: 7 February 2022The complex structure of the plant cell wall differs among different species and tissue types
Using the NCBI Conserved Domain database, we found that the conserved domains of the protein include the MYB-binding domain at 19~76 aa and the SANT domain at 16~64 aa, and PmMYB7 belongs to the SANT protein superfamily (Figure 2A)
Summary
The complex structure of the plant cell wall differs among different species and tissue types. SCWs, which are thicker than the primary cell wall (PCW), are deposited between the PCW and the plasma membrane during the later stages of the cessation of cell growth and division [3]. This SCW mainly includes lignin, cellulose and hemicellulose, which play important roles in the development, mechanical support and waterproofness of vessel walls, as well as in the stress responses of plants [3,4]. Lignin is oxidatively polymerized primarily from three types of monolignols (p-coumaryl alcohol, coniferyl alcohol and sinapyl alcohol) that are synthesized in the cytosol from phenylalanine through successive deamination, reduction, hydroxylation and methylation processes (Figure 1) [5,6,7].
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