A tetraspanin gene regulating auxin response and affecting orchid perianth size and various plant developmental processes

Abstract

The competition between L (lip) and SP (sepal/petal) complexes in P-code model determines the identity of complex perianth patterns in orchids. Orchid tetraspanin gene Auxin Activation Factor (AAF) orthologs, whose expression strongly correlated with the expansion and size of the perianth after P code established, were identified. Virus-induced gene silencing (VIGS) of OAGL6-2 in L complex resulted in smaller lips and the down-regulation of Oncidium OnAAF. VIGS of PeMADS9 in L complex resulted in the enlarged lips and up-regulation of Phalaenopsis PaAAF. Furthermore, the larger size of Phalaenopsis variety flowers was associated with higher PaAAF expression, larger and more cells in the perianth. Thus, a rule is established that whenever bigger perianth organs are made in orchids, higher OnAAF/PaAAF expression is observed after their identities are determined by P-code complexes. Ectopic expression Arabidopsis AtAAF significantly increased the size of flower organs by promoting cell expansion in transgenic Arabidopsis due to the enhancement of the efficiency of the auxin response and the subsequent suppression of the jasmonic acid (JA) biosynthesis genes (DAD1/OPR3) and BIGPETAL gene during late flower development. In addition, auxin-controlled phenotypes, such as indehiscent anthers, enhanced drought tolerance, and increased lateral root formation, were also observed in 35S::AtAAF plants. Furthermore, 35S::AtAAF root tips maintained gravitropism during auxin treatment. In contrast, the opposite phenotype was observed in palmitoylation-deficient AtAAF mutants. Our data demonstrate an interaction between the tetraspanin AAF and auxin/JA that regulates the size of flower organs and impacts various developmental processes.