Exogenous bacterial cellulose induces plant tissue regeneration through the regulation of cytokinin and defense networks

Regeneration is a unique feature of postembryonic development extensively observed in plants. Several hormonal signaling networks govern plant regeneration responses, and while these networks can potentially integrate external cues, the capacity to induce regeneration exogenously is limited and usually confined to meristematic tissues. As bacterial cellulose (BC) contains plant hormones and shows unique physicochemical properties, it provides a valuable tool to investigate the relationships between exogenous cues, hormonal responses and plant regeneration. We demonstrate that BC induces post-wounding regeneration in non-meristematic plant tissues. Furthermore, our results reveal that BC activates an alternative route to standard regenerative programs, with inconsistent activation of previously proposed core regeneration gene regulatory networks, including WOUND INDUCED DEDIFFERENTIATION1 (WIND1), and despite several transcriptional signatures for wounding- and callus-induced regeneration being observed. The BC-specific transcriptional program involves cytokinin signaling, although not exclusively, to promote plant regeneration. Intriguingly, we found a strong induction of plant biotic responses. We identified the WRKY8 transcription factor, known for regulating defense and abiotic stress responses, as a regulator of BC-mediated plant regeneration. WRKY8 activates redox homeostasis genes, which, in turn regulate reactive oxygen accumulation at the wound sites. Particularly, BC increases the superoxide anion content through the WRKY8 network to potentially promote cell proliferation following wounding. Collectively, our results demonstrate that the temporal concurrent activation of the cytokinin and defense responses can be targeted by BC application to promote plant wound regeneration through an alternative route to callus formation. Overall design: To comprehensively address the endogenous regulation and determinants of BC-mediated regeneration we performed transcriptomic analyses through RNA sequencing (RNA-seq) of the wound region. Arabidopsis leaf cuts were covered with BC or left uncovered, and a 1 mm area surrounding the wound was collected at 0, 3, 6 and 24 hpw and analyzed through RNA-seq. Differential gene expression (DEG) analysis was performed to identify transcriptional changes specifically occurring over time in wounded tissue covered with BC