Cytokinin, auxin, and abscisic acid affects sucrose metabolism conduce to de novo shoot organogenesis in rice (Oryza sativa L.) callus

Background: Shoot regeneration frequency in rice callus is still low and highly diverse among rice cultivars. This study aimed to investigate the association of plant hormone signaling and sucrose uptake and metabolism in rice during callus induction and early shoot organogenesis. The immatured seeds of two rice cultivars, Ai-Nan-Tsao 39 (ANT39) and Tainan 11 (TN11) are used in this study. Results: Callus formation is earlier, callus fresh weight is higher, but water content is significant lower in ANT39 than in TN11 while their explants are inoculated on callus induction medium (CIM). Besides, the regeneration frequency is prominently higher in ANT39 (similar to 80%) compared to TN11 callus (0%). Levels of glucose, sucrose, and starch are all significant higher in ANT39 than in TN11 either at callus induction or early shoot organogenesis stage. Moreover, high expression levels of Cell wall-bound invertase 1, Sucrose transporter 1 (OsSUT1) and OsSUT2 are detected in ANT39 at the fourth-day in CIM but it cannot be detected in TN11 until the tenth-day. It suggested that ANT39 has higher callus growth rate and shoot regeneration ability may cause from higher activity of sucrose uptake and metabolism. As well, the expression levels of ORYZA SATIVA RESPONSE REGULATOR 1 (ORR1), PIN-formed 1 and Late embryogenesis-abundant 1, representing endogenous cytokinin, auxin and ABA signals, respectively, were also up-regulated in highly regenerable callus, ANT39, but only ORR1 was greatly enhanced in TN11 at the tenth-day in CIM. Conclusion: Thus, phytohormone signals may affect sucrose metabolism to trigger callus initiation and further de novo shoot regeneration in rice culture.