R2R3-MYB gene pairs in Populus: evolution and contribution to secondary wall formation and flowering time

Abstract

In plants, the R2R3-MYB gene family contains many pairs of paralogous genes, which play the diverse roles in developmental processes and environmental responses. The paper reports the characterization of 81 pairs of Populus R2R3-MYB genes. Chromosome placement, phylogenetic, and motif structure analyses showed that these gene pairs resulted from multiple types of gene duplications and had five different gene fates. Tissue expression patterns revealed that most duplicated genes were specifically expressed in the tissues examined. qRT-PCR confirmed that nine pairs were highly expressed in xylem, of which three pairs (PdMYB10/128, PdMYB90/167, and PdMYB92/125) were further functionally characterized. The six PdMYBs were localized to the nucleus and had transcriptional activities in yeast. The heterologous expression of PdMYB10 and 128 in Arabidopsis increased stem fibre cell-wall thickness and delayed flowering. In contrast, overexpression of PdMYB90, 167, 92, and 125 in Arabidopsis decreased stem fibre and vessel cell-wall thickness and promoted flowering. Cellulose, xylose, and lignin contents were changed in overexpression plants. The expression levels of several genes involved in secondary wall formation and flowering were affected by the overexpression of the six PdMYBs in Arabidopsis. This study addresses the diversity of gene duplications in Populus R2R3-MYBs and the roles of these six genes in secondary wall formation and flowering control.

Identification of Norway Spruce MYB-bHLH-WDR Transcription Factor Complex Members Linked to Regulation of the Flavonoid Pathway

“…Together with their contrasting transcriptional responses to hormones and abiotic stress, our observations suggest that the gene duplication that gave rise to PaMYB32 and PaMYB33 was followed by a sub-functionalization of the paralogs, as predicted by the model on functional divergence of recently duplicated regulatory genes (Grotewold, 2005). Similar evolutionary changes have been observed for R2R3-MYB family TFs in several angiosperms (Dias et al, 2003; Chai et al, 2014; Zhao and Bartley, 2014). …”

“…The more generalized late-biosynthesis-gene upregulation seen in PaMYB33 and PaMYB35 overexpression lines and the expression pattern of PaMYB30, PaMYB31, PaMYB33 , and PaMYB35 , which showed a higher degree of tissue specificity and more restricted responses to abiotic stress compared to PaMYB29 and PaMYB32 , suggests that these R2R3-MYB family TFs may perform their regulatory role in particular organs or distinct cell types. Such organ specificity is reported for Arabidopsis ' subgroup 7 R2R3-MYB members (Stracke et al, 2007), for paralogous R2R3-MYB genes, Pd MYB2 and Pd MYB20, in poplar (Chai et al, 2014) and to some extent among conifer subgroup 4 R2R3-MYB family TFs (Bedon et al, 2007, 2010). …”

Activation tagging of Arabidopsis POLYGALACTURONASE INVOLVED IN EXPANSION2 promotes hypocotyl elongation, leaf expansion, stem lignification, mechanical stiffening, and lodging

“…A transcription factor, MlWRKY12 , from Miscanthus is involved in pith secondary wall formation and promotes flowering (Yu et al ., ). The expression of several poplar PdMYB genes in Arabidopsis affects secondary wall formation, and can either promote or delay flowering (Chai et al ., ). In this work, we observed that when PGX2 was overexpressed, PGX2 AT plants flowered earlier than Col controls, possibly due to enhanced expression of the flowering gene FT (Figure h).…”

KNAT2/6b, a class I KNOX gene, impedes xylem differentiation by regulating NAC domain transcription factors in poplar

“…In addition, expression of MYB002 (an ortholog of AtMYB46 and AtMYB83), MYB021 (AtMYB46 and AtMYB83), MYB031 (AtMYB69), MYB090 (AtMYB52 and AtMYB54), MYB127 (AtMYB67), MYB128 (AtMYB103) and MYB158 (AtMYB69) (Chai et al, 2014;Zhao & Bartley, 2014) was significantly downregulated in PagKNAT2/6b OE plants. All of these genes could activate the expression of secondary wall biosynthesis genes, and their dominant repression transgenic plants showed altered secondary wall thickening of fibers and vessels in Arabidopsis (Zhong et al, 2007(Zhong et al, , 2008McCarthy et al, 2009).…”