Interaction between row‐type genes in barley controls meristem determinacy and reveals novel routes to improved grain

Abstract

Summary Hordeum species develop a central spikelet flanked by two lateral spikelets at each inflorescence node. In ‘two‐rowed’ spikes, the central spikelet alone is fertile and sets grain, while in ‘six‐rowed’ spikes, lateral spikelets can also produce grain. Induced loss‐of‐function alleles of any of five Six‐rowed spike ( VRS ) genes ( VRS 1‐5 ) cause complete to intermediate gains of lateral spikelet fertility. Current six‐row cultivars contain natural defective vrs1 and vrs5 alleles. Little information is known about VRS mechanism(s). We used comparative developmental, expression and genetic analyses on single and double vrs mutants to learn more about how VRS genes control development and assess their agronomic potential. We show that all VRS genes repress fertility at carpel and awn emergence in developing lateral spikelets. VRS 4, VRS 3 and VRS 5 work through VRS 1 to suppress fertility, probably by inducing VRS 1 expression. Pairing vrs3 , vrs4 or vrs5 alleles increased lateral spikelet fertility, despite the presence of a functional VRS 1 allele. The vrs3 allele caused loss of spikelet identity and determinacy, improved grain homogeneity and increased tillering in a vrs4 background, while with vrs5 , decreased tiller number and increased grain weight. Interactions amongst VRS genes control spikelet infertility, determinacy and outgrowth, and novel routes to improving six‐row grain.

Of floral fortune: tinkering with the grain yield potential of cereal crops

“…Vrs3 encodes a putative Jumonji C‐type H3K9me2/3 histone demethylase, a regulator of chromatin state (Bull et al ., ; van Esse et al ., ). These studies reveal that combining a vrs3 mutant allele with six‐rowed vrs1 and vrs5 alleles leads to increased grain size in the lateral spikelets and greater grain uniformity (Bull et al ., ; Zwirek et al ., ). Vrs4 encodes a LATERAL ORGAN BOUNDARY (LOB)‐domain‐containing transcription factor (Koppolu et al ., ).…”

“…The gene is the barley ortholog of maize ramosa2 , a regulator of inflorescence branching (Bortiri et al ., ). Transcript network analysis suggests that Vrs3 and Vrs4 suppress lateral floret fertility as upstream regulators of Vrs1 (Koppolu et al ., ; Sakuma et al ., ; Zwirek et al ., ).…”

Natural Genetic Variation Underlying Tiller Development in Barley (Hordeum vulgare L)

“…Although variation in HvCEN affects the number of spikelets per spike, there is no evidence that it affects the number of fertile florets per spikelet, so it is likely that another gene in this region is associated with spike row-type. HvMADS15, a MADS-box gene homologous to APETALA1/FRUITFULL (HORVU2Hr1G063800, 58.76 cM) is a more likely candidate because its expression is nearly undetectable in spike row-type vrs3/int-c double mutants, indicating a role in spike row-type determination (Zwirek et al 2019). VRS3 encodes a histone demethylase, and mutants have an intermediate spike row-type like int-c mutants (van Esse et al 2017;Bull et al 2017).…”

Grain yield, agronomic traits, and protein content of two- and six-row barley genotypes under terminal drought conditions

“…On the other hand, in six-row barley genotypes, in addition to the central spikelet, two lateral spikelets are also fertile and can develop grain. These two types generally differ in their end use: six-row barley is mainly used as feed due to its higher grain PC and less uniform grain size and weight compared with two-row barley (Lang et al, 2013;Zwirek et al, 2019), while two-row barley is more often used as a malting material in beer production, producing high malt extract, lighter color, and less enzyme content than the six-row type (Gupta et al, 2010). The aim of this study was to evaluate the effect of terminal drought conditions simulated by defoliation on grain yield, agronomic traits, and protein content of 25 barley genotypes of both barley types and to examine a correlation of these traits under optimal and stress conditions.…”