Finlayson, S. A. | bioRxiv Science

bioRxiv2026

Photosynthetic assimilate determines branch size and biomass more than branch number in Arabidopsis

Shoot branching is a primary determinant of plant form and crop yield, yet whether auxin or carbon supply is the proximal regulator of branching remains contested. In Arabidopsis, an earlier report that exogenous auxin fails to restore apical dominance after decapitation has been taken to weaken the case for auxin, and several studies have proposed that sugars are the primary regulator. Resolving this has been difficult because most perturbations of sugar status also disturb auxin. Here, we revisit the control of Arabidopsis branching using well-controlled, largely unperturbed plants and approaches designed to isolate each pathway. Contrary to the earlier report, apically applied auxin restored the suppression of rosette branching after decapitation, placing Arabidopsis in line with other species. In a dataset of 718 plants, cauline and rosette branching were weakly but significantly negatively correlated, consistent with a polar-auxin-transport-based model and contrary to a previous conclusion of no relationship. Removing all rosette leaves at bolting slowed bud growth but did not alter the final number of branches. Varying photosynthetic photon flux density across six natural accessions, analyzed by piecewise structural equation modeling, showed that photoassimilate acted far more strongly on the mass deposited into branches than on whether a bud initiates a branch. We conclude that auxin remains a major regulator of apical dominance in Arabidopsis, and that photosynthetic assimilate, while required as a substrate for branch growth, contributes little to determining branch number but more to branch size and biomass.

plant biology↗

bioRxiv2026

RRTF1 promotes touch-responses in Arabidopsis shoots independent of jasmonic acid

Plants acclimate to mechanical stimuli such as touch and wind via thigmomorphogenesis, a suite of developmental responses that alter their growth and architecture. However, the early signaling mechanisms translating mechanoperception into long-term morphological changes remain incompletely understood. We investigated the role of the rapidly touch-induced transcription factor RRTF1 (REDOX RESPONSIVE TRANSCRIPTION FACTOR 1) in these processes. Phenotypically, under aggressive mechanical stimulation, rrtf1 mutant exhibited attenuated stunting (less height reduction). This suggests a key role for RRTF1 in promoting thigmomorphogenic responses under severe mechanical stimuli, though the rrtf1 mutant responded similarly to wild-type under gentle, repeated brushing. The alleviation of growth stunting in rrtf1 was largely jasmonic acid (JA)-independent. Transcriptome analysis at 10 minutes post-touch revealed that rrtf1 mutant maintained approximately 86% of wild-type touch-responsive gene expression. Nevertheless, RRTF1 modulated specific regulons, partly through an interplay with WRKY transcription factors, as evidenced by altered TF binding motif enrichment in RRTF1-specific differentially expressed genes. We conclude that RRTF1 acts as a modulator of early touch signaling in Arabidopsis shoots. It is not essential for the bulk of the initial transcriptional response but fine-tunes specific gene sets and plays a crucial role in calibrating long-term thigmomorphogenic development, particularly by promoting growth inhibition under severe mechanical stimulation. This study provides insights into the alleviation of touch-induced growth inhibition in rrft1 mutant, which might be relevant to breeding for crops that are planted in high density and experience constant physical contact with neighboring plants.

plant biology↗