Involvement of endogenous IAA and ABA in the regulation of arbuscular mycorrhizal fungus on rooting of tea plant (Camellia sinensis L.) cuttings

Background: Adventitious root (AR) formation is the key step for successful cutting propagation of tea plants (Camellia sinensis L.). Studies showed that arbuscular mycorrhizal fungus (AMF) can promote the rooting ability, and auxin pathway in basal stem of cuttings was involved in this process. However, auxin and abscisic acid (another important regulator on AR formation) in the other parts of cuttings at different rooting stages responding to AMF inoculation are not well studied. Therefore, in this paper, contents, enzymes and genes related to these two plant hormones were comprehensively determined aiming to unveil how endogenous indole-3-acetic acid (IAA) and abscisic acid (ABA) involve in the AMF regulating AR development of tea cuttings.

Results: Inoculating with AMF significantly increased the proportion of cuttings at S2 stage (AR formation), which was more than twice as much as the control. And the total rooting rate in mycorrhizal treatment was also higher than that in the control with an increase of 8.66%. Enzyme activity assays showed that except for decreased polyphenol oxidase (PPO) activity at the S3 stage and peroxidase (POD) activity in middle stem of S3 stage, AMF inoculation increased activities of POD, PPO, superoxide dismutase (SOD) and catalase (CAT) to varying degrees in leaf, middle stem and basal stem of tea cuttings. After inoculation with AMF, the indoleacetic acid oxidase (IAAO) activity decreased to a certain extent in the first three stages of tea cuttings, which showed a trend of 'low-high-low' in the basal stem of all treatments. Besides, there was a significantly positive correlation between SOD activity and AR formation, especially for the proportion of cuttings at S2 and S3 stages. Higher IAA level and IAA/ABA ratio was found in basal stem of cuttings at S1 stage induced by AMF, which promoting the AR formation as revealed by correlation analysis. At the same time, AMF significantly elevated the level of IAA in leaf at S1 stage. By screening differentially expressed genes (DEGs) related to IAA and ABA pathways, together with redundant analysis, it was indicated that auxin biosynthesis and transport, as well as ABA transport and signal transduction, were involved in AMF regulating the rooting of tea cuttings.

Conclusions: Overall, both endogenous IAA and ABA played roles in the regulation of AR formation of tea cuttings by AMF inoculating, enriching the theoretical basis of AMF regulating rooting of cuttings and providing foundations for cutting propagation of tea plants.