Roles of BdUNICULME4 and BdLAXATUM‐A in the non‐domesticated grass Brachypodium distachyon

Abstract

SUMMARY In cultivated grasses, tillering, spike architecture and seed shattering represent major agronomical traits. In barley, maize and rice, the NOOT‐BOP‐COCH‐LIKE (NBCL) genes play important roles in development, especially in ligule development, tillering and flower identity. However, compared with dicots, the role of grass NBCL genes is underinvestigated. To better understand the role of grass NBCLs and to overcome any effects of domestication that might conceal their original functions, we studied TILLING nbcl mutants in the non‐domesticated grass Brachypodium distachyon. In B. distachyon, the NBCL genes BdUNICULME4 (CUL4) and BdLAXATUM‐A (LAXA) are orthologous, respectively, to the barley HvUniculme4 and HvLaxatum‐a, to the maize Zmtassels replace upper ears1 and Zmtassels replace upper ears2 and to the rice OsBLADE‐ON‐PETIOLE1 and OsBLADE‐ON‐PETIOLE2/3. In B. distachyon, our reverse genetics study shows that CUL4 is not essential for the establishment of the blade–sheath boundary but is necessary for the development of the ligule and auricles. We report that CUL4 also exerts a positive role in tillering and a negative role in spikelet meristem activity. On the other hand, we demonstrate that LAXA plays a negative role in tillering, positively participates in spikelet development and contributes to the control of floral organ number and identity. In this work, we functionally characterized two new NBCL genes in a context of non‐domesticated grass and highlighted original roles for grass NBCL genes that are related to important agronomical traits.

The wild grass Brachypodium distachyon as a developmental model system

“…Importantly, most of the work we will describe would not have been possible without the resources described above. There are a number of additional developmental processes being studied in B. distachyon; important contributions include for example, cell wall biology (see Coomey et al, 2020) and references therein), vascular development (Sakai et al, 2021;Smertenko et al, 2019), pleiotropic genes like the NOOT-BOP-COCH-LIKE genes (Magne et al, 2020), seed germination (Wolny et al, 2018), species-specific aspects of abscission zone formation (Yu et al, 2020), and even thigmomorphogenesis-the developmental response to touch (Coomey et al, 2021). We apologize for not being able to cover all the developmental work done with B. distachyon due to space limitations.…”

The BOP‐type co‐transcriptional regulator NODULE ROOT1 promotes stem secondary growth of the tropical Cannabaceae tree Parasponia andersonii

“…This paralogous gene problem is also apparent for NBCL genes. Populus species have two NBCL paralogs, called BLADE‐ON‐PETIOLE‐LIKE1 and 2 ( BPL1 and BPL2 ; Magne et al, 2020), whereas P. andersonii only possesses a single gene, namely PanNOOT1 . Besides the reduced genome complexity of P. andersonii, efficient protocols for in vitro propagation, transformation and CRISPR‐Cas9 genome editing are also available for this species (Wardhani et al, 2019; van Zeijl et al, 2018).…”

“…NBCL genes encode co‐transcriptional regulators that can also act as E3 ubiquitin ligase adapters regulating protein homeostasis (Jun et al, 2010; Zhang et al, 2017). NBCLs are conserved in both dicots and monocots, and were shown to be involved in a myriad of developmental processes (Dong et al, 2017; Hepworth and Pautot, 2015; Jost et al, 2016; Khan et al, 2014; Magne et al, 2020; Tavakol et al, 2015; Toriba et al, 2019; Wang et al, 2016). NBCL proteins are involved in boundary formation.…”

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

“…In Solanum lycoperscum, three BLADE-ON-PETIOLE paralogs (SlBOP1, 2 and 3) also control inflorescence architecture (Xu et al, 2016;Izhaki et al, 2018) and compound leaf complexity (Ichihashi et al, 2014). This regulation of inflorescence architecture by NBCLs is also observed in several monocot species such as Brachypodium distachyon, Oryza sativa, Hordeum vulgare and Zea mays (Tavakol et al, 2015;Jost et al, 2016;Dong et al, 2017;Toriba et al, 2019;Magne et al, 2020).…”