HAPLESS13-Mediated Trafficking of STRUBBELIG Is Critical for Ovule Development in Arabidopsis

Abstract

Planar morphogenesis, a distinct feature of multicellular organisms, is crucial for the development of ovule, progenitor of seeds. Both receptor-like kinases (RLKs) such as STRUBBELIG (SUB) and auxin gradient mediated by PIN-FORMED1 (PIN1) play instructive roles in this process. Fine-tuned intercellular communications between different cell layers during ovule development demands dynamic membrane distribution of these cell-surface proteins, presumably through vesicle-mediated sorting. However, the way it’s achieved and the trafficking routes involved are obscure. We report that HAPLESS13 (HAP13)-mediated trafficking of SUB is critical for ovule development. HAP13 encodes the μ subunit of adaptor protein 1 (AP1) that mediates protein sorting at the trans-Golgi network/early endosome (TGN/EE). The HAP13 mutant, hap13-1, is defective in outer integument growth, resulting in exposed nucellus accompanied with impaired pollen tube guidance and reception. SUB is mis-targeted in hap13-1. However, unlike that of PIN2, the distribution of PIN1 is independent of HAP13. Genetic interference of exocytic trafficking at the TGN/EE by specifically downregulating HAP13 phenocopied the defects of hap13-1 in SUB targeting and ovule development, supporting a key role of sporophytically expressed SUB in instructing female gametogenesis.

Arabidopsis Chloroplast protein for Growth and Fertility1 (CGF1) and CGF2 are essential for chloroplast development and female gametogenesis

“…5a-h). Wrinkled, white ovules are usually consequences of failed fertilization [17,18]. To determine whether this was the case, we examined mature ovules by confocal laser scanning microscopy (CLSM).…”

“…Whole-mount embryo clearing were performed as described [19]. CLSM of optical sections were performed as described [18]. The 4th true leaves of 3 WAG plants were cut into small pieces for plastic sections and TEMs as performed as described [27,30].…”

The crossroads of receptor‐mediated signaling and endocytosis in plants

“…At present, RME is documented for many plant RLKs and RLPs, including the Arabidopsis RLKs, BRI1 (Russinova et al ; Geldner et al ), BAK1 (Russinova et al ), SERK1 (Kwaaitaal et al ), FLS2, ELONGATION FACTOR TU RECEPTOR (EFR) (Mbengue et al ), PEP RECEPTOR1 (PEPR1) (Ortiz‐Morea et al ), CLV1 (Nimchuk et al ), ACR4 (Gifford et al ), STRUBBELIG (SUB) (Wang et al ), LYK5 and CHITIN ELICITOR RECEPTOR KINASE1 (CERK1) (Erwig et al ), and the tomato ( Solanum lycopersicum ) RLPs, SlEix2 (Ron and Avni 2004; Sharfman et al ) and the Cf proteins (Postma et al ).…”

“…In plants, many RLKs, such as BRI1, BAK1, SERK1, FLS2, CERK1, ACR4, SUB, and the rice XANTHOMONAS RESISTANCE 21 (OsXa21), accumulate in BFA bodies and are recycled (Geldner et al 2003;Russinova et al 2004;Gifford et al 2005;Kwaaitaal et al 2005;Chen et al 2010;Beck et al 2012;Wang et al 2016;Erwig et al 2017). However, recycling is mostly associated with the inactive receptors, because recycling of ligand-bound receptors has not yet been demonstrated in plants.…”

Vacuolar trafficking in pollen tube growth and guidance

“…Both pollen tube growth and guidance was compromised by VPS41 loss-of-function, 28 suggesting a key role of vacuolar delivery in pollen tube guidance. Interestingly, MDIS1, the recently identified LURE receptor at the pollen tubes, undergoes LURE-induced endocytosis, 29 suggesting the involvement of vacuolar trafficking in directional growth of pollen tubes upon sensing the female cues. However, no direct evidence has been shown to demonstrate an essential role of its endocytosis for pollen tube growth and guidance.…”