StHAB1, a negative regulatory factor in abscisic acid signaling, plays crucial roles in potato drought tolerance and shoot branching.

Abscisic acid (ABA) is critical in drought tolerance and plant growth. Group A protein type 2C phosphatases (PP2Cs) are negative regulators of ABA signaling and plant adaptation to stress. Knowledge about the functions of potato group A PP2Cs is limited. Here, we report that the potato group A PP2C StHAB1 is broadly expressed in potato plants and strongly induced by ABA and drought. Suppression of StHAB1 enhanced potato ABA sensitivity and drought tolerance, whereas overexpression of the dominant mutant StHAB1G276D compromised ABA sensitivity and drought tolerance. StHAB1 interacts with almost all ABA receptors and the Snf1-Related Kinase OST1. Suppressing StHAB1 and overexpressing StHAB1G276D alter potato growth morphology; notably, overexpression of StHAB1G276D causes excessive shoot branching. RNA-sequencing analyses identified that the auxin efflux carrier genes StPIN3, StPIN5, and StPIN8 were up-regulated in StHAB1G276D-overexpressing axillary buds. Correspondingly, the auxin concentration was reduced in StHAB1G276D-overexpressing axillary buds, consistent with the role of auxin in repressing lateral branch outgrowth. The expression of BRANCHED1s (StBRC1a and StBRC1b) was unchanged in StHAB1G276D-overexpressing axillary buds, suggesting that StHAB1G276D overexpression does not cause axillary bud outgrowth via regulation of BRC1 expression. Our findings demonstrate that StHAB1 is vital in potato drought tolerance and shoot branching.

Leaves and stolons transcriptomic analysis provide insight into the role of phytochrome F in potato flowering and tuberization.

Photoperiod plays a critical role in controlling the formation of sexual or vegetative reproductive organs in potato. Although StPHYF-silenced plants overcome day-length limitations to tuberize through a systemic effect on tuberigen StSP6A expression in the stolon, the comprehensive regulatory network of StPHYF remains obscure. Therefore, the present study investigated the transcriptomes of StPHYF-silenced plants and observed that, in addition to known components of the photoperiodic tuberization pathway, florigen StSP3D and other flowering-related genes were activated in StPHYF-silenced plants, exhibiting an early flowering response. Additionally, grafting experiments uncovered the long-distance effect of StPHYF silencing on gene expression in the stolon, including the circadian clock components, flowering-associated MADSs, and tuberization-related regulatory genes. Similar to the AtFT-AtAP1 regulatory module in Arabidopsis, the present study established that the AP1-like StMADS1 functions downstream of the tuberigen activation complex (TAC) and that suppressing StMADS1 inhibits tuberization in vitro and delays tuberization in vivo. Moreover, the expression of StSP6A was downregulated in StMADS1-silenced plants, implying the expression of StSP6A may be feedback-regulated by StMADS1. Overall, these results reveal that the regulatory network of StPHYF controls flowering and tuberization and targets the crucial tuberization factor StMADS1 through TAC, thereby providing a better understanding of StPHYF-mediated day-length perception during potato reproduction.

Phytochrome F plays critical roles in potato photoperiodic tuberization.

The transition to tuberization contributes greatly to the adaptability of potato to a wide range of environments. Phytochromes are important light receptors for the growth and development of plants, but the detailed functions of phytochromes remain unclear in potato. In this study, we first confirmed that phytochrome F (StPHYF) played essential roles in photoperiodic tuberization in potato. By suppressing the StPHYF gene, the strict short-day potato genotype exhibited normal tuber formation under long-day (LD) conditions, together with the degradation of the CONSTANTS protein StCOL1 and modulation of two FLOWERING LOCUS T (FT) paralogs, as demonstrated by the repression of StSP5G and by the activation of StSP6A during the light period. The function of StPHYF was further confirmed through grafting the scion of StPHYF-silenced lines, which induced the tuberization of untransformed stock under LDs, suggesting that StPHYF was involved in the production of mobile signals for tuberization in potato. We also identified that StPHYF exhibited substantial interaction with StPHYB both in vitro and in vivo. Therefore, our results indicate that StPHYF plays a role in potato photoperiodic tuberization, possibly by forming a heterodimer with StPHYB.