OsAP79 induced the reduction of IAA accumulation in the
root thereby inhibiting root elongation
Plant APs are involved in precursor protein processing, protein
degradation, PCD, leaf senescence, stress resistance, and disease
resistance senescence (Chen et al ., 2015). Nevertheless, no
insect resistance function has been reported until now. Here, we found
that the overexpression of OsAP79 could significantly increase
rice resistance against sucking insects by reducing BPH weight gain and
honeydew excretion (Figure 2e and 2f). Our findings improve the
understanding of the functions of the AP family. Plant phytohormones
play an important role in growth and immunity. For instance, auxin, a
negative regulator of plant immunity, has long been known to actively
modify plant defense (Navarro et al ., 2006). This is done by
reducing the rice auxin content via enhanced disease resistance to
fungal and bacterial pathogens by constitutively expressingOsGH3.8 (Ding et al ., 2008) and OsGH3.1 (Domingoet al ., 2009). OE lines of OsAP79 had a significantly low
IAA content, which caused enhanced BPH resistance; the opposite result
was detected in the knockout lines. Our results indicate thatOsAP79 positively confers BPH resistance by negatively regulating
IAA content (Figure 4f).
Auxin is an essential hormone that regulates the development and growth
of plants. In this study, OE lines of OsAP79 presented shorter
roots than NIP due to decreased IAA content, and knockout lines showed
the opposite result (Figure 4b, 4d, and 4f). This is another indicator
of a positive correlation between root length and IAA content. The OE
lines of OsGH3s also had reduced content of free IAA, and
presented differences in morphological phenotypes, such as dwarfism, as
well as fewer lateral or crown roots (Zhang et al ., 2009, Fuet al ., 2011, Du et al ., 2012). Moreover, the apple geneMsGH3.5 functions as an auxin response gene that restricts plant
shoot and root development (Zhao et al ., 2020). Therefore, we
propose that IAA is an important regulatory hormone ofOsAP79 in BPH resistance and root length.