PpeTAC1 promotes the horizontal growth of branches in peach trees and is a member of a functionally conserved gene family found in diverse plants species

Abstract

SUMMARYTrees are capable of tremendous architectural plasticity, allowing them to maximize their light exposure under highly competitive environments. One key component of tree architecture is the branch angle, yet little is known about the molecular basis for the spatial patterning of branches in trees. Here, we report the identification of a candidate gene for the br mutation in Prunus persica (peach) associated with vertically oriented growth of branches, referred to as 'pillar' or 'broomy'. Ppa010082, annotated as hypothetical protein in the peach genome sequence, was identified as a candidate gene for br using a next generation sequence-based mapping approach. Sequence similarity searches identified rice TAC1 (tiller angle control 1) as a putative ortholog, and we thus named it PpeTAC1. In monocots, TAC1 is known to lead to less compact growth by increasing the tiller angle. In Arabidopsis, an attac1 mutant showed more vertical branch growth angles, suggesting that the gene functions universally to promote the horizontal growth of branches. TAC1 genes belong to a gene family (here named IGT for a shared conserved motif) found in all plant genomes, consisting of two clades: one containing TAC1-like genes; the other containing LAZY1, which contains an EAR motif, and promotes vertical shoot growth in Oryza sativa (rice) and Arabidopsis through influencing polar auxin transport. The data suggest that IGT genes are ancient, and play conserved roles in determining shoot growth angles in plants. Understanding how IGT genes modulate branch angles will provide insights into how different architectural growth habits evolved in terrestrial plants.

Screening of molecular markers linked to dwarf trait in crape myrtle by bulked segregant analysis

“…Studies of plant architecture have focused on the biology of this trait, beginning with the introduction of lodging-resistant semidwarf wheat and rice mutants that led to the Green Revolution in the 1960s (Peng et al, 1999). The genetic mechanism of plant architecture in crops has been improved (Gallavotti et al, 2010), and batch of genes modulating plant height have been successfully cloned (Dardick et al, 2013).…”

Arabidopsis LAZY1 is a peripheral membrane protein of which the carboxy-terminal fragment potentially interacts with microtubules

“…In fact, ZmLAZY1 is involved in tassel development as well as gravitropism (Dong et al 2013) while AtLAZY1 does not seem to be (Yoshihara et al 2013). In contrast, LAZY1 is involved in shoot gravitropism in all the plant species so far examined (Dardick et al 2013). …”

“…The LAZY1 protein has been initially identified as a key regulator in gravity perception of rice shoots (Li et al 2007;Yoshihara and Iino 2007). These proteins are conserved in a range of higher plant species (Dardick et al 2013). lazy1 mutants of rice (Li et al 2007;Yoshihara and Iino 2007), maize (Dong et al 2013) and Arabidopsis (Yoshihara et al 2013) show impaired shoot gravitropic responses, indicating that LAZY1 is involved in a conserved mechanism of gravitropism.…”

“…While LAZY1 acts positively in gravitropism, TAC1 affects gravitropism negatively, and lacks the ca. 40 amino acid-long C-terminal region (including region V) that is more or less conserved in LAZY1 subfamily (Dardick et al 2013). How these structural differences contribute to their contrasting function is poorly understood.…”

“…Shoots generally grow upwards to get more light energy for photosynthesis, while roots grow downwards to obtain water and nutrients (Morita 2010). In agriculture, shoot gravitropism of trees and crops is important for managing plantations (Dardick et al 2013) and root gravitropism is important for overcoming drought stress in the field (Uga et al 2013). Hence a better understanding and modification of gravitropism are likely to improve yields of crops and other agricultural products.…”