Root hair‐specific expansins modulate root hair elongation in rice

Abstract

SUMMARYRoot hair growth requires intensive cell-wall modification. This study demonstrates that root hair-specific expansin As, a sub-clade of the cell wall-loosening expansin proteins, are required for root hair elongation in rice (Oryza sativa L.). We identified a gene encoding EXPA17 (OsEXPA17) from a rice mutant with short root hairs. Promoter::reporter transgenic lines exhibited exclusive OsEXPA17 expression in root hair cells. The OsEXPA17 mutant protein (OsexpA17) contained a point mutation, causing a change in the amino acid sequence (Gly104 fi Arg). This amino acid alteration is predicted to disrupt a highly conserved disulfide bond in the mutant. Suppression of OsEXPA17 by RNA interference further confirmed requirement for the gene in root hair elongation. Complementation of the OsEXPA17 mutant with other root hair EXPAs (OsEXPA30 and Arabidopsis EXPA7) can restore root hair elongation, indicating functional conservation of these root hair EXPAs in monocots and dicots. These results demonstrate that members of the root hair EXPA sub-clade play a crucial role in root hair cell elongation in Graminaceae.

Root Hair Development in the Grasses: What We Already Know and What We Still Need to Know

“…Three expansins, which are encoded by HvEXPB1 (Kwasniewski and Szarejko, 2006), OsEXPB5, and OsEXPA17 (Won et al, 2010;ZhiMing et al, 2011), have been proven to be involved in RH initiation and elongation. Mutant analysis showed that the HvEXPB1 transcript is present in the root but not in the shoot (Kwasniewski and Szarejko, 2006).…”

“…A rice line that produced RHs that were 70% shorter than those of the wild type has been shown to harbor a single nucleotide variant for OsEXPA17. This gene is specifically transcribed in the RH, and its promoter also includes an RH-specific ciselement (ZhiMing et al, 2011). The mutant phenotype proved to be partially reversible by constitutively expressing OsEXPA30, which is a gene encoding an RH-specific expansin.…”

Rice Homeodomain Protein WOX11 Recruits a Histone Acetyltransferase Complex to Establish Programs of Cell Proliferation of Crown Root Meristem

“…For instance, CSLF6, a putative cellulose-like synthase family member, is required for rice primary and adventitious root development through a phosphate accumulation-dependent pathway (Jin et al, 2015). Rice expansin genes, including OsEXPA8, OsEXPA17, and OsEXPB5, are reported to modulate root development (Won et al, 2010;ZhiMing et al, 2011;Ma et al, 2013). In addition, CESAs (cellulose synthases) are delivered to cell plate and deposit cellulose via phragmoplast-associated vesicles during cell division in Arabidopsis root (Miart et al, 2014).…”

Inducible Repression of Multiple Expansin Genes Leads to Growth Suppression during Leaf Development

“…However, the number of reports showing that repression of expansin gene expression actually leads to a repression in growth is surprisingly limited (Cho and Cosgrove, 2000;Zenoni et al, 2004;ZhiMing et al, 2011). Part of the reason for this is that expansins are encoded by relatively large gene families, leading to potential problems of genetic redundancy when single gene members are mutated or their expression is repressed .…”

“…Despite this potential complication, reports have been made in which a clear growth phenotype resulted from the suppression of a single expansin gene (Cho and Cosgrove, 2000;Choi et al, 2003;Zenoni et al, 2004;ZhiMing et al, 2011). These investigations have targeted root hairs and petals in dicots and the mesocotyl and coleoptile in monocots, but to date, only one experiment relating the suppression of expansin gene expression to leaf growth has been reported.…”