The expression of a rice secondary wall-specific cellulose synthase gene, OsCesA7, is directly regulated by a rice transcription factor, OsMYB58/63

Abstract

A rice MYB transcription factor, OsMYB58/63, was found to directly upregulate the expression of a rice secondary wall-specific cellulose synthase gene, cellulose synthase A7 ( OsCesA7 ); in contrast, the Arabidopsis putative orthologs AtMYB58 and AtMYB63 have been shown to specifically activate lignin biosynthesis. Although indirect evidence has shown that grass plants are similar to but partially different from dicotyledonous ones in transcriptional regulation of lignocellulose biosynthesis, little is known about the differences. This study showed that a rice MYB transcription factor, OsMYB58/63, directly upregulated the expression of a rice secondary wall-specific cellulose synthase gene, cellulose synthase A7 (OsCesA7). Gene co-expression analysis showed that, in rice, OsMYB58/63 and several rice MYB genes were co-expressed with genes encoding lignocellulose biosynthetic enzymes. The expression levels of OsMYB55/61, OsMYB55/61-L, OsMYB58/63, and OsMYB42/85 were commonly found to be high in culm internodes and nodes. All four MYB transcription factors functioned as transcriptional activators in yeast cells. OsMYB58/63 most strongly transactivated the expression of OsCesA7 in rice protoplasts. Moreover, recombinant OsMYB58/63 protein was bound to two distinct cis-regulatory elements, AC-II and SMRE3, in the OsCesA7 promoter. This is in sharp contrast to the role of Arabidopsis orthologs, AtMYB58 and AtMYB63, which had been reported to specifically activate lignin biosynthesis. The promoter analysis revealed that AC elements, which are the binding sites for MYB58 and MYB63, were lacking in cellulose and xylan biosynthetic genes in Arabidopsis, but present in cellulose, xylan, and lignin biosynthetic genes in rice, implying that the difference of transcriptional regulation between rice and Arabidopsis is due to the distinct composition of promoters. Our results provide a new insight into transcriptional regulation in grass lignocellulose biosynthesis.

Gene regulatory networks for lignin biosynthesis in switchgrass (Panicum virgatum)

“…Although both PvMYB58/63 and AtMYB58/63 function as activators of lignin biosynthesis, an increased expression of secondary wall‐associated cellulose synthase and xylan synthase genes, as well as flavonoid biosynthesis genes, was observed here in PvMYB58/63‐OX plants but not in Arabidopsis MYB58/63 overexpressors (Zhou et al ., ). Considering that OsMYB58/63 could also up‐regulate secondary wall‐related cellulose synthase genes in transactivation assay (Noda et al ., ), and the overexpression of SbMYB60 (the ortholog of AtMYB58/63 ) in sorghum altered cell wall cellulose and xylan content (Scully et al ., ), we suggest that the MYB58/63 clade in grasses may function as a broader activator regulating both lignin and cellulose/hemicellulose biosynthesis, rather than possessing the ‘lignin‐ specific regulator’ function ascribed to AtMYB58/63 in Arabidopsis.…”

Overexpression of SbMyb60 in Sorghum bicolor impacts both primary and secondary metabolism

“…Notably, monocot TFs can have different targets and different impacts on secondary cell wall biosynthesis relative to their dicot orthologs. For example, in Oryza sativa (rice), overexpression of OsMyb58 and OsMyb63 directly activates CesA, unlike in Arabidopsis (Noda et al, 2015). Other variations in the regulation of secondary wall biosynthesis are likely to exist between monocots and dicots because of the extensive differences in secondary cell wall composition and plant anatomy.…”

Expression Patterns of MYB (V-myb Myeloblastosis Viral Oncogene Homolog) Gene Family in Resistant and Susceptible Tung Trees Responding to Fusarium Wilt Disease

“…The ABA-dependent signaling pathway regulates stress-inducible gene expression through several positive and negative regulators and the ABA-signaling mutant aba2-1, shows increased resistance to the necrotrophic fungal pathogen F. oxysporum in Arabidopsis [6]. The homologous gene of VmMYB013 in rice directly upregulates the expression of a secondary wall-specific cellulose synthase gene, cellulose synthase A7 (OsCesA7) [46]. This gene's homologue in Arabidopsis thaliana is a transcriptional regulator specifically activating lignin biosynthetic genes during secondary wall formation [47].…”