KOMPEITO, an Atypical Arabidopsis Rhomboid-Related Gene, Is Required for Callose Accumulation and Pollen Wall Development

Abstract

Fertilization is a key event for sexually reproducing plants. Pollen–stigma adhesion, which is the first step in male–female interaction during fertilization, requires proper pollen wall patterning. Callose, which is a β-1.3-glucan, is an essential polysaccharide that is required for pollen development and pollen wall formation. Mutations in CALLOSE SYNTHASE 5 (CalS5) disrupt male meiotic callose accumulation; however, how CalS5 activity and callose synthesis are regulated is not fully understood. In this paper, we report the isolation of a kompeito-1 (kom-1) mutant defective in pollen wall patterning and pollen–stigma adhesion in Arabidopsis thaliana. Callose was not accumulated in kom-1 meiocytes or microspores, which was very similar to the cals5 mutant. The KOM gene encoded a member of a subclass of Rhomboid serine protease proteins that lacked active site residues. KOM was localized to the Golgi apparatus, and both KOM and CalS5 genes were highly expressed in meiocytes. A 220 kDa CalS5 protein was detected in wild-type (Col-0) floral buds but was dramatically reduced in kom-1. These results suggested that KOM was required for CalS5 protein accumulation, leading to the regulation of meiocyte-specific callose accumulation and pollen wall formation.

Genome‐wide identification, gene expression and haplotype analysis of the rhomboid‐like gene family in wheat (Triticum aestivum L.)

“…In rice, inhibiting the expression of OsDER1 led to decreased GL and width via changing starch and protein body I morphology (Qian et al., 2018). In Arabidopsis , the RBL8 affected the morphological changes of pollen outer wall, and RBL10 plays a role in floral development (Kanaoka et al., 2022).…”

“…The rhomboid‐like ( RBL ) family genes encode a family of transmembrane serine proteases, which typically contain six or seven transmembrane domains and play vital roles in the intracellular signal transduction by modifying transmembrane protein substrates (Ha et al., 2013; Koonin et al., 2003; Lemberg & Freeman, 2007). RBL proteins have been reported to be involved in regulating various cytological processes, such as growth factor signaling transduction, endoplasmic reticulum (ER)‐associated protein degradation, and cell proliferation and death (Adrain & Cavadas, 2020; Adrain et al., 2011; Bock et al., 2022; Greenblatt et al., 2011; Kanaoka et al., 2022; Li et al., 2015; Urban et al., 2001).…”

“…The RBL10 gene has been reported to be necessary for the processes of root growth, floral development, fertility, and photoprotection (Lavell et al., 2021; Thompson et al., 2012). A recent study showed that KOM, a Rhomboid serine protease protein, was involved in the regulation of meiocyte‐specific callose accumulation and pollen wall formation (Kanaoka et al., 2022). In addition, ER‐associated degradation factor Derlin‐1, as a rhomboid protease, was required for the dislocation of the mutant α‐1 antitrypsin from the ER (Greenblatt et al., 2011).…”