Alteration in Auxin Homeostasis and Signaling by Overexpression Of PINOID Kinase Causes Leaf Growth Defects in Arabidopsis thaliana

Abstract

In plants many developmental processes are regulated by auxin and its directional transport. PINOID (PID) kinase helps to regulate this transport by influencing polar recruitment of PIN efflux proteins on the cellular membranes. We investigated how altered auxin levels affect leaf growth in Arabidopsis thaliana. Arabidopsis mutants and transgenic plants with altered PID expression levels were used to study the effect on auxin distribution and leaf development. Single knockouts showed small pleiotropic growth defects. Contrastingly, several leaf phenotypes related to changes in auxin concentrations and transcriptional activity were observed in PID overexpression (PIDOE) lines. Unlike in the knockout lines, the leaves of PIDOE lines showed an elevation in total indole-3-acetic acid (IAA). Accordingly, enhanced DR5-visualized auxin responses were detected, especially along the leaf margins. Kinematic analysis revealed that ectopic expression of PID negatively affects cell proliferation and expansion rates, yielding reduced cell numbers and small-sized cells in the PIDOE leaves. We used PIDOE lines as a tool to study auxin dose effects on leaf development and demonstrate that auxin, above a certain threshold, has a negative affect on leaf growth. RNA sequencing further showed how subtle PIDOE-related changes in auxin levels lead to transcriptional reprogramming of cellular processes.

A leaf shape mutant provides insight into PINOID Serine/Threonine Kinase function in cucumber (Cucumis sativus L.)

“…PINOID kinase has been shown to regulate auxin transport at cellular membranes and its overexpression, or knockout, causes leaf growth defects in Arabidopsis (Saini et al ). Similarly conserved domains and near evolutionary distance with high reliability indicate the PINOID proteins from other plants are orthologous, or paralogous, with that in cucumber and these proteins may have similar functions in regulating auxin transport and leaf growth.…”

“…In this study, the higher expression of YUCCA4 and two other IAA synthesis‐related genes, CYP79B3 and NIT , was consistent with the increase in IAA concentration, suggesting that rl is an auxin‐overproducing mutant. Overexpression of PID would increase the IAA content in Arabidopsis , however, IAA content also increased in the Arabidopsis pid mutant (Saini et al ). In cucumber, the expression levels of auxin synthesis‐related genes was upregulated (Figure B).…”

“…ARF s can activate or inhibit the expression of other primary/early auxin response genes by interacting with auxin response elements ( AuxRE ) with these genes (Hagen and Guilfoyle ). In WT plants, as the concentration of auxin increases, auxin combines with TIR (auxin‐transport inhibitor response), causing Aux/IAA ubiquitination and degradation, releasing the ARF s, and eventually promoting ARF gene expression (Wang et al ; Saini et al ). In the rl mutant, low expression of ARF s leads to a defect in a regulatory pathway that results in auxin overproduction.…”

“…Transgenic plants overexpressing PID showed elevated IAA content, which affected cell proliferation and expansion rates, resulting in reduced cell numbers and small‐sized cells in the leaves. In contrast to the overexpression lines, knockout lines and pid mutants showed a slightly bigger rosette area, three cotyledons, and were sterile (Saini et al ). BARREN INFLORESCENCE2 , an ortholog of PID , is a key regulator of inflorescence and vegetative development in maize, and the bif2 mutant has fewer branches, spikelets, florets, and floral organs (Mcsteen et al ).…”

Arabidopsis ERF109 regulates auxin transport-related genes in root development

“…The overexpression of PID causes the reduction of lateral auxin transport due to the preferential stimulation of downward directed PAT to the root apex by PID , which leads to the loss of auxin of root apex and peripheral cells, and subsequently results in the reduction of lateral roots, shortened hypocotyl and root, and the loss of gravitropism and phototropism (Benjamins et al , 2001; Haga and Sakai, 2015; Saini et al , 2017a; Sukumar et al , 2009; Willige and Chory, 2015). Recent studies have revealed that PID is a crucial contributor of the regulation of apical-basal PIN polarity (Friml et al , 2004; Kleine-Vehn et al , 2009; Saini et al , 2017b; Wang et al , 2019; Zourelidou et al , 2014). The mechanisms of PID -mediated PIN polarity alteration have been unraveled (Christensen et al , 2000; Dory et al , 2018; Geldner et al , 2003; Kleine-Vehn et al , 2009; Michniewicz et al , 2007).…”