OsAP79 affects root growth via the regulation of IAA content
To gain insight into the physiological function of OsAP79 , we made focused phenotypic observations of the root, given the apparently high expression ofOsAP79 in this organ. In a greenhouse, we measured the root length of NIP, OE, and knockout lines every 5 days until day 30. No significant difference in root length was observed among the three genotypic lines. However, 30 days after germination, the roots of the OE line were the shortest, while those for the knockout lines were the longest (Figure 4a and 4c). Moreover, compared with NIP, a significantly shorter root of OE and a longer one of the knockout lines was detected when they grew for up to 75 days (Figure 4b and 4d). These results suggest that OsAP79 can very negatively regulate root growth, especially at the adult stage.
A previous study has indicated that IAA content can directly regulate root growth (Shen et al ., 2019). A lower IAA content was detected in the resistant rice line than in the susceptible line after BPH feeding, whereas the SA content had the opposite pattern (Zhang et al ., 2022). Therefore, the contents of IAA and SA in the NIP, OE, and knockout lines were measured. Compared to NIP, the IAA content of OE lines significantly decreased, but it increased in the knockout lines (Figure 4f). However, no significant differences in SA content were observed among the three genotypic lines (Figure 4g). These results show that OsAP79 can negatively regulate IAA content, which contributes to root growth.
It was noted that IAA content regulated by OsAP79 can affect root growth. To test whether the application of additional IAA contributes to rice root growth, 15-day-old lines of OE, knockout, and NIP were treated with IAA. Consequently, compared with normally growing plants, the relative root length increased by 1.87 cm and 2.33 cm for the OE lines, and 1.13 cm for NIP; however, it was -0.1 cm and -0.443 cm for the knockout lines when they were treated with additional IAA for 5 days (Figure 4e). The same trend was observed when cells were treated for 10 days. These results indicate that additional IAA can contribute to the root growth in OE lines, but restricts root growth in knockout lines.