2018 ASHS Annual Conference

Plant architecture is intimately tied to environmental signals. One example of this is the relationship between light and shoot organ orientation. Light is known to affect the angle at which branches grow, and growth angle of branches influences the amount of light to which the plant has access. A number of genetic factors are also known to influence branch angles. Among these are genes in the IGT gene family, which contain TILLER ANGLE CONTROL1 (TAC1) and LAZY1. Loss of TAC1 gene expression results in narrow, upright branch angles, whereas loss of LAZY1 leads to wider or sometimes downward angles. These phenotypes have been shown in a wide range of species, including rice, corn, Arabidopsis, and recently demonstrated by our group in plum (Prunus domestica). Here we demonstrate a connection between light and the genetic components underlying branch angle. Dark-grown plants exhibit a phenotype similar to that of tac1 mutants, which led us to find a number of light-related motifs upstream of the TAC1 gene. TAC1 expression is light regulated, does not show a strong circadian rhythm, and is not strongly influenced by Red/Far-Red or Blue light signaling. However, TAC1 expression is highly responsive to photosynthetic inhibitors, suggesting that it functions as a target of photosynthetic signals to regulate branch angles in a light-dependent manner.