A homolog of Blade-On-Petiole 1 and 2 (BOP1/2) controls internode length and homeotic changes of the barley inflorescence

Abstract

Inflorescence architecture in small-grain cereals has a direct effect on yield and is an important selection target in breeding for yield improvement. We analyzed the recessive mutation laxatum-a (lax-a) in barley (Hordeum vulgare), which causes pleiotropic changes in spike development, resulting in (1) extended rachis internodes conferring a more relaxed inflorescence, (2) broadened base of the lemma awns, (3) thinner grains that are largely exposed due to reduced marginal growth of the palea and lemma, and (4) and homeotic conversion of lodicules into two stamenoid structures. Map-based cloning enforced by mapping-by-sequencing of the mutant lax-a locus enabled the identification of a homolog of BLADE-ON-PETIOLE1 (BOP1) and BOP2 as the causal gene. Interestingly, the recently identified barley uniculme4 gene also is a BOP1/2 homolog and has been shown to regulate tillering and leaf sheath development. While the Arabidopsis (Arabidopsis thaliana) BOP1 and BOP2 genes act redundantly, the barley genes contribute independent effects in specifying the developmental growth of vegetative and reproductive organs, respectively. Analysis of natural genetic diversity revealed strikingly different haplotype diversity for the two paralogous barley genes, likely affected by the respective genomic environments, since no indication for an active selection process was detected.The inflorescence is the most prominent part of smallgrain cereal plants, producing the carbohydrate-rich grains that are harvested for food, feed, and fiber. However, our understanding of the genetic factors that regulate inflorescence architecture remains limited. What is clear is that the appearance and shape of the inflorescence has been under constant visual selection since early domestication and is still ongoing in modern plant breeding due to the impact of inflorescence architecture on crop yield. For instance, in barley (Hordeum vulgare), strong selection has been exerted on spontaneously occurring alleles of nonbrittle rachis1 (btr1) and btr2 that prevent dehiscence of the rachis at maturity (Pourkheirandish et al., 2015), six-rowed spike1 (vrs1) that determines whether the inflorescence exhibits two or six rows of grain (Komatsuda et al., 2007), and nudum (nud) that controls whether the grain is hulled or hull-less (Taketa et al., 2008). Ultimately, knowing all of the genes that control cereal inflorescence architecture will provide targets for understanding and exploiting natural or induced genetic diversity toward improving both yield potential and end-use characteristics.The barley inflorescence or spike forms an unbranched main rachis carrying triplets of sessile single-floreted

Control of inflorescence architecture in tomato by BTB/POZ transcriptional regulators

“…For example, whereas Arabidopsis BOP1 seems to have a more prominent role in leaf development, BOP2 functions more during reproductive growth (Khan et al 2014). Similarly, recent work in barley has shown that two BOP homologs regulate tillering, ligule development, proximal-distal leaf patterning, and several aspects of inflorescence development, including internode length and floral organ development (Tavakol et al 2015;Jost et al 2016). Our data suggest that SlBOP2 is the dominant family member in tomato.…”

“…Our data suggest that SlBOP2 is the dominant family member in tomato. However, the earlier flowering and extreme simplification of inflorescences in CR-slbop triple mutants contrasts the comparatively weak bop flowering and inflorescence phenotypes in Arabidopsis and barley (Hepworth et al 2005;Norberg et al 2005;Xu et al 2010;Andres et al 2015;Khan et al 2015;Jost et al 2016). Although some inflorescence defects are shared among the three species (e.g., elongated internodes and abnormal pedicel orientation), it is striking that eliminating BOP activity in Arabidopsis results in a weak loss of IM determinacy, whereas the fewflowered inflorescences of tomato CR-slbop mutants are based on precocious meristem maturation that leads to enhanced SIM termination.…”

“…S3J-N). Several of these reproductive defects, particularly changes in pedicel orientation and internode elongation, were reminiscent of bop mutants in Arabidopsis and barley (Xu et al 2010;Khan et al 2012;Jost et al 2016). Thus, similar to BOP genes in other species, the tomato SlBOP family functions in multiple developmental contexts (Couzigou et al 2012;Wu et al 2012;Ichihashi et al 2014;Khan et al 2014;Tavakol et al 2015;Jost et al 2016).…”

Ideal crop plant architecture is mediated by tassels replace upper ears1, a BTB/POZ ankyrin repeat gene directly targeted by TEOSINTE BRANCHED1

“…Members of the BTB/POZ clade of ankyrin repeat proteins have a wide range of functions (25) including establishment of floral and inflorescence meristem determinacy (45)(46)(47), but those most similar to tru1 appear to have a clear function in specifying leaf cell identities. The founding members of this clade, BLADE ON PETIOLE 1 and 2, display ectopic distal blade tissue growing down the petiole and lack of stipules (24,48).…”

Barley Developmental Mutants: The High Road to Understand the Cereal Spike Morphology

“…This is a recessive mutation (lax-a) with a pleiotropic effect: long rachis internode, large base of lemma awns, and the transformation of lodicules into two additional stamens. Consequently, the Laxatum mutant shows five anthers instead of the regular three [13,24]. A panel of major genes is involved in the control of spike density, as demonstrated by the genetic analysis of several morphological mutants.…”