A Ds-insertion mutant of OSH6 (Oryza sativa Homeobox 6) exhibits outgrowth of vestigial leaf-like structures, bracts, in rice

Abstract

OSH6 (Oryza sativa Homeobox6) is an ortholog of lg3 (Liguleless3) in maize. We generated a novel allele, termed OSH6-Ds, by inserting a defective Ds element into the third exon of OSH6, which resulted in a truncated OSH6 mRNA. The truncated mRNA was expressed ectopically in leaf tissues and encoded the N-terminal region of OSH6, which includes the KNOX1 and partial KNOX2 subdomains. This recessive mutant showed outgrowth of bracts or produced leaves at the basal node of the panicle. These phenotypes distinguished it from the OSH6 transgene whose ectopic expression led to a "blade to sheath transformation" phenotype at the midrib region of leaves, similar to that seen in dominant Lg3 mutants. Expression of a similar truncated OSH6 cDNA from the 35S promoter (35S::DeltaOSH6) confirmed that the ectopic expression of this product was responsible for the aberrant bract development. These data suggest that OSH6-Ds interferes with a developmental mechanism involved in bract differentiation, especially at the basal nodes of panicles.

Relationship between Symptoms and Gene Expression Induced by the Infection of Three Strains of Rice dwarf virus

“…The homeobox gene family is associated with the development and morphogenesis of plants [33], [34]. The expression of many HD-zip-type homeobox genes was suppressed by RDV infection, except for the genes classified in HD-zip I, which were predominantly activated by RDV infection (Figure 8A).…”

TWI1 regulates cell‐to‐cell movement of OSH15 to control leaf cell fate

“…In Arabidopsis, KNOX family genes are repressed at the leaf primordium stage of development, and this is essential for correct cell specification, differentiation and pattern formation (Lin et al ., ; Kumar et al ., ). OSH15 is the only KNOX family member expressed in the base of the leaf primordium, and it is noteworthy that overexpression of OSH15, as well as OSH1 and OSH6 , in rice produces an abnormal SAM and defective vascular bundles (Sentoku et al ., ; Nagasaki et al ., ; Park et al ., ). Our findings that OSH15 is present in leaf primordia (Fig.…”

“…Consistent with this hypothesis, OSH15 overexpression results in a knotted leaf phenotype in which vascular patterning is disrupted (Nagasaki et al, 2001), along with a reduction in both sclerenchyma and BS cells. In addition, ectopic expression of OSH6 was shown to produce a 'blade-to-sheath transformation' phenotype (Park et al, 2007). However, as OSH15 mRNA can be detected in the basal region of developing wild-type rice leaf primordia (Sentoku et al, 1999), the role for this and other OSH genes in rice leaf development remains unknown.…”

Bract suppression regulated by the miR156/529-SPLs-NL1-PLA1 module is required for the transition from vegetative to reproductive branching in rice

“…A common defect of the reproductive branch is that its subtending leaf (bract) is de-repressed, which can be taken as the marker event to evaluate the heterochronic-vegetative growth during reproductive organogenesis (Kawakatsu et al, 2009). Several genes underlying bract suppression have been isolated in Arabidopsis, maize, rice, barley, and wheat; these genes differ between monocotyledon and dicotyledon plants (Chuck et al, 2007(Chuck et al, , 2010Ferrandiz et al, 2000;Hepworth et al, 2006;Houston et al, 2012;Ikeda et al, 2019;Karim et al, 2009;Kawakatsu et al, 2006Kawakatsu et al, , 2009Li et al, 2019;Miyoshi et al, 2004;Muller-Xing et al, 2014;Ohno et al, 2004;Park et al, 2007;Sauret-Gueto et al, 2013;Walla et al, 2020;Wang et al, 2009b;Weigel et al, 1992;Whipple et al, 2010), indicating that the transition between vegetative and reproductive branches may be controlled by lineage-specific genes. Besides leaf outgrowth, flowers are converted into the leafy shoots in the bract de-repression mutants ap1 cal ful, puchi bop1 bop2, and lfy in Arabidopsis (Ferrandiz et al, 2000;Karim et al, 2009;Weigel et al, 1992), while panicle branches are transformed into the leafy shoots in the bract derepression mutants plastochron1 (pla1), pla2/leafy head2 (lhd2), and pla3 in rice (supplemental Figure 1D and 1E) (Itoh et al, 1998;Miyoshi et al, 2004;Kawakatsu et al, 2006Kawakatsu et al, , 2009Xiong et al, 2006), implying that bract suppression is in general tightly linked to the irreversible developmental patterns of the reproductive branches.…”

“…In rice, Neck Leaf1 (NL1), Oryza sativa (Os) Homeobox6 (OSH6), Verticillate Rachis (RI, also known as Seed Shattering 5), RI-LIKE1 (RIL1, also known as QTL of Seed Shattering in Chromosome 1), PLA1, PLA2, and PLA3 are all involved in bract suppression (Miyoshi et al, 2004;Kawakatsu et al, 2006Kawakatsu et al, , 2009Konishi et al, 2006;Park et al, 2007;Wang et al, 2009b;Yoon et al, 2014;Ikeda et al, 2019). Compared with other genes, the effects of OSH6, RI, and RIL1 appeared to be minor as only very tiny outgrown bracts are observed in their mutants.…”