Genetics of Tillering in Rice and Barley

Abstract

Tillering, or the production of lateral branches (i.e., culms), is an important agronomic trait that determines shoot architecture and grain production in grasses. Shoot architecture is based on the actions of the apical and axillary meristems (AXMs). The shoot apical meristem (SAM) produces all aboveground organs, including AXMs, leaves, stems, and inflorescences. In grasses like rice (Oryza sativa L.) and barley (Hordeum vulgare L.), vegetative AXMs form in the leaf axil of lower leaves of the plant and produce tillers (branches). Tiller development is characterized by three stages, including (i) AXM initiation, (ii) bud development, and (iii) outgrowth of the axillary bud into a tiller. Each tiller has the potential to produce a seed-bearing inflorescence and, hence, increase yield. However, a balance between number and vigor of tillers is required, as unproductive tillers consume nutrients and can lead to a decreased grain production. Because of its agronomic and biological importance, tillering has been widely studied, and numerous works demonstrate that the control of AXM initiation, bud development, and tillering in the grasses is via a suite of genes, hormones, and environmental conditions. In this review, we describe the genes and hormones that control tillering in two key cereal crops, rice and barley. In addition, we discuss how the development of new genomics tools and approaches, coupled with the synteny between the rice and barley genomes, are accelerating the isolation of barley genes underlying tillering phenotypes.A t the global level, the most important cereal crops are maize (Zea mays L.), rice, wheat (Triticum aestivum L.) and barley (H. vulgare spp. vulgare), with a total of 2.4 billion tons produced annually at a value of >446 billion

Yield-related traits characterization of local upland rice cultivars originated from East and North Kalimantan, Indonesia

“…Tiller relates directly to the grain production in grass crops, since each tiller has the capacity to generate panicles. Many studies prior to understanding factors controlling and affecting the tillering capacity in rice in terms of genetics investigation Hussain et al 2014;Uddin et al 2016), and environmental factors (Assuero and Tognetti, 2009) have been conducted comprehensively. Genetically, tillering capacity is controlled by many genes (Yan et al 1998;Miyamoto et al 2004;Luo et al 2012).…”

The Barley Uniculme4 Gene Encodes a BLADE-ON-PETIOLE-Like Protein That Controls Tillering and Leaf Patterning

“…Tillering or vegetative branching is one of the most important components of shoot architecture in cereals because it contributes directly to grain yield (Kebrom et al, 2013;Hussien et al, 2014) and is involved in plant plasticity in response to environmental cues and stresses (Mohapatra et al, 2011;Agusti and Greb, 2013). The shoot apical meristem initiates a series of repetitive units called phytomers, each consisting of a leaf, a node, an internode, and an axillary meristem (AXM) located in the axil between the leaf and the shoot axis (Sussex, 1989).…”

“…Although sharing some key steps in their development, tillers differ from lateral branches in eudicots in that they can produce adventitious roots and grow independently from the main plant shoot. Primary tillers arising from the main culm initiate new axillary buds that may, in turn, develop into secondary tillers and so on in a reiterative pattern (Hussien et al, 2014).…”

“…A complex combination of differential gene expression in conjunction with hormonal signaling and responses and environmental cues determines the number and location of axillary branches (Hussien et al, 2014). A number of evolutionarily conserved genetic pathways control axillary branching in both monocots and eudicots (Kebrom et al, 2013;Janssen et al, 2014).…”

“…For example, reduced-branching mutant phenotypes are conferred by mutations in the orthologous GRAS (for GIBBERELLIC ACID-INSENSITIVE, REPRESSOR of GA1, and SCARECROW) genes LATERAL SUPPRESSOR in Arabidopsis (Arabidopsis thaliana), LATERAL SUPPRESSOR in tomato (Solanum lycopersicum), and MONOCULM1 in rice (Oryza sativa; Li et al, 2003). However, the molecular mechanisms that control branching in eudicots are not completely conserved with tiller development in grasses (Kebrom et al, 2013;Hussien et al, 2014;Waldie et al, 2014). For example, the reduced-branching mutations in the REGULATOR OF AXILLARY MERISTEMS1, REGULATOR OF AX-ILLARY MERISTEMS2, REGULATOR OF AXILLARY MERISTEMS3, and BLIND genes of Arabidopsis and tomato (Schmitz et al, 2002;Keller et al, 2006;Müller et al, 2006) are conserved in eudicots but have not been identified in monocot genomes (Keller et al, 2006;Müller et al, 2006).…”