Brachypodium distachyon UNICULME4 and LAXATUM-A are redundantly required for development

Abstract

In cultivated grasses, tillering, leaf and inflorescence architecture, as well as abscission ability, are major agronomical traits. In barley (Hordeum vulgare), maize (Zea mays), rice (Oryza sativa), and brachypodium (Brachypodium distachyon), NOOT-BOP-COCH-LIKE (NBCL) genes are essential regulators of vegetative and reproductive development. Grass species usually possess two-to-four NBCL copies and until now a single study in O. sativa showed that the disruption of all NBCL genes strongly altered O. sativa leaf development. To improve our understanding of the role of NBCL genes in grasses, we extended the study of the two NBCL paralogs BdUNICULME4 (CUL4) and BdLAXATUM-A (LAXA) in the non-domesticated grass B. distachyon. For this, we applied reversed genetics and generated original B. distachyon single and double nbcl mutants by CRISPR-Cas9 approaches and genetic crossing between nbcl TILLING mutants. Through the study of original single laxa CRISPR-Cas9 null alleles, we validated functions previously proposed for LAXA in tillering, leaf patterning, inflorescence and flower development and also unveiled roles for these genes in seed yield. Furthermore, the characterization of cul4laxa double mutants revealed essential functions for nbcl genes in B. distachyon development, especially in the regulation of tillering, stem cell elongation and secondary cell wall composition as well as for the transition towards the reproductive phase. Our results also highlight recurrent antagonist interactions between NBCLs occurring in multiple aspects of B. distachyon development.

Fast-track transformation and genome editing in Brachypodium distachyon

“…In comparison to previous reports, the protocol presented herein cuts one to two months to the creation of Bd transgenics [ 6 , 32 ] or CRISPR/Cas9-induced mutants [ 18 , 22 , 27 ], with no observable reduction in transformation efficiency. In routine procedures, we typically use ca.…”

The transcriptional co-regulators NBCL1 and NBCL2 redundantly coordinate aerial organ development and root nodule identity in legumes

“…In S. lycopersicum, three BOP genes participate in the diversity of leaf complexity through the repression of leaflet formation (Izhaki et al, 2018). Furthermore, in monocots, such as H. vulgare, O. sativa and B. distachyon, NBCLs are also required for the leaf ligule and auricles development (Tavakol et al, 2015;Jost et al, 2016;Toriba et al, 2019;Magne et al, 2020;Liu et al, 2021). The Pscoch1 mutant was already described for stipule, flower and nodule developmental alterations and showed a strong penetrance (Yaxley et al, 2001;Ferguson and Reid, 2005;Couzigou et al, 2012).…”

“…In the grasses H. vulgare, O. sativa and B. distachyon, the NBCL genes are also required for the patterning of the leaf, especially for the patterning of the ligular region (Tavakol et al, 2015;Toriba et al, 2019;Magne et al, 2020;Liu et al, 2021). In O. sativa, the OsBOP genes determine the leaf sheath-blade ratio through the activation of proximal sheath differentiation and suppression of distal blade differentiation (Toriba et al, 2019).…”

Regulation of secondary growth by poplar BLADE-ON-PETIOLE genes in Arabidopsis

“…BTB-ankyrin proteins from both subclades can also function as E3 ubiquitin ligase adaptors involved in regulating protein abundance ( Fu et al., 2012 ; Zhang et al., 2017 ; Chahtane et al., 2018 ; He et al., 2020 ). In monocots and dicots, BOPs contribute to a surprisingly large number of developmental processes, including lignin deposition as a defense ( Zhang et al., 2019 ) and during secondary growth ( Khan et al., 2012b ; Woerlen et al., 2017 ; Shen et al., 2021 ; Liu et al., 2022 ).…”

“…Phenotypic defects in bop1 bop2 double mutants are concentrated at lateral organ boundaries resulting in elongated leafy petioles, five-petalled flowers with a subtending bract, and defects in abscission ( Hepworth et al., 2005 ; Norberg et al., 2005 ; McKim et al., 2008 ). In monocots and dicots, BOP1 and BOP2 paralogs participate in many of the same developmental processes ( Wu et al., 2012 ; Tavakol et al., 2015 ; Couzigou et al., 2016 ; Jost et al., 2016 ; Xu et al., 2016 ; Toriba et al., 2019 ; Magne et al., 2020 ; Liu et al., 2022 ).…”