Genetic Fine‐Mapping of a Quantitative Trait Locus (QTL) Associated with Embryogenic Tissue Culture Response and Plant Regeneration Ability in Maize (Zea mays L.)

Abstract

Embryogenic and regenerable tissue cultures are widely utilized in plant transformation, clonal propagation, and biological research applications. Germplasm utilized in those applications are limited, however, due to genotype-dependent culture response. The goal of this study was to identify genomic regions controlling embryogenic and regenerable tissue culture response in the globally important crop, maize ( L.), toward the long-term objective of developing approaches for genotype-independent plant genetic engineering and clonal propagation systems. An inbred maize line, WCIC2, nearly-isogenic to reference inbred B73, was developed by phenotypic selection and molecular marker analysis. WCIC2 has over 50x increase in tissue culture response relative to the recurrent parent, B73. This line was used to genetically fine-map a region on chromosome 3 controlling embryogenic and regenerable tissue culture response to a 23.9 Mb region. WCIC2 and derivatives will be useful materials to enable maize research in a genetic background similar to B73, and our genetic mapping results will advance research to identify causal genes controlling somatic embryo formation and plant regeneration in maize.

Highly efficient and genotype-independent barley gene editing based on anther culture

“…Most commercially important varieties are recalcitrant or marginally transformable at present. Because culture responses for callus induction and plant regeneration are polygenic, QTL mapping and gene identification for this complex trait have been performed in Arabidopsis , rice, maize, barley, and some other crops to identify underlying genetic mechanisms ( Bolibok and Rakoczy-Trojanowska, 2006 ; Chen et al., 2007 ; Fan et al., 2012 ; Ikeuchi et al., 2013 ; Motte et al., 2014 ; Salvo et al., 2018 ). The latest breakthrough in genotype dependence is the specific expression of two major transcription factors, Wuschel2 ( Wus2 ) and Baby Boom ( Bbm ), from maize, which function as morphogenic regulators that stimulate and promote somatic cells to form embryos that develop into whole plants in a range of monocots, including maize, sorghum, sugarcane, and indica rice ( Lowe et al., 2016 ; Mookkan et al., 2017 ).…”

Genome assembly of the maize inbred line A188 provides a new reference genome for functional genomics

“…Recently, by using the F 3:4 population derived from B73 and WCIC2 (a near isogenic line of B73 containing several A188 segments), a locus associated with embryogenic and regenerative capabilities of immature embryo was fine-mapped within a 3.06 M region (chr3:178772856-181826658) based on the B73 reference genome, suggesting that the genes harbored by the A188 segment caused the high callus formation ratio (Salvo et al, 2018).…”

“…Moreover, previous studies have demonstrated that changes in gene expression can be induced during somatic embryogenesis to respond to tissue culture process (Ge et al, 2017;Salvo et al, 2018;Shen et al, 2012;Zhang et al, 2014). Based on the reported transcriptome data of A188 (Zhang et al, 2014), four of the 99 A188 genes within the mapped QTL were regulated by more than 8 folds in different stages of immature embryo culture, relative to control.…”

“…The copyright holder for this preprint this version posted March 16, 2021. ; https://doi.org/10.1101/2021.03.15.435372 doi: bioRxiv preprint Lai et al, 2010;Schnable et al, 2009;Springer et al, 2009). The temperate line A188 (Gacheri et al, 2015), with high frequency of EC initiation (Armstrong et al, 1992;Salvo et al, 2018), is a desirable material to study the molecular mechanism underlying EC formation and regeneration. Due to the difference between A188 genome and B73 reference genome, these identified QTLs for embryo culture response have not been cloned so far, limiting their applications in improving EC formation capability.…”

Natural Variation in Plant Pluripotency and Regeneration

“…QTL mapping of regeneration traits has been attempted in several other cereal crops such as maize [ 104 , 105 , 106 ], wheat [ 107 , 108 , 109 ], and barley [ 110 , 111 , 112 ] ( Table 2 ). Early studies in maize using the highly and lowly regenerable A188 and B73 inbred lines identified a major QTL on chromosome 3 [ 104 ] that was recently exploited to create a germplasm with enhanced tissue culture responses, nearly isogenic to the elite B73 [ 106 ]. Fine mapping of this locus revealed a 3053-kb region containing multiple candidate genes such as ALDOLASE 1 ( ALD1 ), ZmWOX2A, and ZmWOX5B .…”