TILLER ANGLE CONTROL 1 modulates plant architecture in response to photosynthetic signals

Abstract

Light serves as an important environmental cue in regulating plant architecture. Previous work had demonstrated that both photoreceptor-mediated signaling and photosynthesis play a role in determining the orientation of plant organs. TILLER ANGLE CONTROL 1 (TAC1) was recently shown to function in setting the orientation of lateral branches in diverse plant species, but the degree to which it plays a role in light-mediated phenotypes is unknown. Here, we demonstrated that TAC1 expression was light dependent, as expression was lost under continuous dark or far-red growth conditions, but did not drop to these low levels during a diurnal time course. Loss of TAC1 in the dark was gradual, and experiments with photoreceptor mutants indicated this was not dependent upon red/far-red or blue light signaling, but partially required the signaling integrator CONSTITUTIVE PHOTOMORPHOGENESIS 1 (COP1). Overexpression of TAC1 partially prevented the narrowing of branch angles in the dark or under far-red light. Treatment with the carotenoid biosynthesis inhibitor norflurazon or the PSII inhibitor 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) led to loss of TAC1 expression similar to dark or far-red conditions, but expression increased in response to the PSI inhibitor paraquat. Treatment of adult plants with norflurazon resulted in upward growth angle of branch tips. Our results indicate that TAC1 plays an important role in modulating plant architecture in response to photosynthetic signals.

Opposing influences of TAC1 and LAZY1 on Lateral Shoot Orientation in Arabidopsis

“…We previously reported that overexpression of TAC1 in plum trees resulted in wider branch angles 17 . However, we also reported TAC1 overexpression only partially complemented the tac1 Arabidopsis mutant phenotype, and in 24-hour light or dark conditions TAC1 overexpression in Col had little effect on branch angle 3,18 . In contrast, 35 S::AtLAZY4/DRO1 in Arabidopsis exhibited more vertically oriented lateral shoots as a result of narrower branch angles, as well as upward curled leaves 6 .…”

“…Plant material, Genotyping, and Branch Angle Measurements. The Arabidopsis tac1, lazy1, prom-LAZY1::GUS, and 35 S::TAC1 plants were previously described 3,4,18 . The tac1;lazy1 homozygous double mutant lines were generated by crossing the single mutants.…”

“…However, species-wide interpretations of results from maize should be cautioned because in addition to its role in gravitropism and shoot architecture, LAZY1 is also essential for tassel and ear development in maize 5 .In contrast to the mechanistic knowledge about LAZY1, much less is known about TAC1. Its function in promoting wide lateral shoot angles is dosage dependent and light regulated 3,[13][14][15][16][17][18][19][32][33][34] . TAC1 expression has been detected in shoot tissues in peach, poplar, and Arabidopsis, with higher expression detected in apical regions 3,16,34 .…”

Transcriptome profiles reveal that gibberellin-related genes regulate weeping traits in crape myrtle

“…In poplar, the overexpression of the LAZY1 gene reduces branch angles, whereas the overexpression of tiller angle control 1 (TAC1) increased the branch angle and promoted an outward branch growth orientation 9 . Similarly, plants with reduced or no TAC1 expression exhibit more vertical shoot angles, as observed in Arabidopsis, maize, rice, and peach [10][11][12][13][14] .…”

Switching the Direction of Stem Gravitropism by Altering Two Amino Acids in AtLAZY1

“…Dardick et al (2013) showed that region II of LAZY genes contains a GwL(A/T)GT motif, which places LAZY genes within a larger family, IGT, to which the Tiller Angle Control 1 (TAC1) gene belongs. Interestingly, TAC1 functionally opposes LAZY by increasing the tiller angle in rice (Yu et al, 2007) and branch angles in peach (Prunus persica) trees (Dardick et al, 2013) and Arabidopsis inflorescences (Waite and Dardick, 2018).…”