The Arabidopsis AGC kinases NDR2/4/5 interact with MOB1A/1B and play important roles in pollen development and germination

Abstract

Pollen formation and pollen tube growth are essential for the delivery of male gametes into the female embryo sac for double fertilization. Little is known about the mechanisms that regulate the late developmental process of pollen formation and pollen germination. In this study, we characterized a group of Arabidopsis AGC kinase proteins, NDR2/4/5, involved in pollen development and pollen germination. The NDR2/4/5 genes are mainly expressed in pollen grains at the late developmental stages and in pollen tubes. They function redundantly in pollen formation and pollen germination. At the tricellular stages, the ndr2 ndr4 ndr5 mutant pollen grains exhibit an abnormal accumulation of callose, precocious germination and burst in anthers, leading to a drastic reduction in fertilization and a reduced seed set. NDR2/4/5 proteins can interact with another group of proteins (MOB1A/1B) homologous to the MOB proteins from the Hippo signaling pathway in yeast and animals. The Arabidopsis mob1a mob1b mutant pollen grains also have a phenotype similar to that of ndr2 ndr4 ndr5 pollen grains. These results provide new evidence demonstrating that the Hippo signaling components are conserved in plants and play important roles in sexual plant reproduction.

NDR/LATS‐family protein kinase genes are indispensable for embryogenesis in Arabidopsis

“…NDR4, NDR6, and NDR8 are phylogenetically close to each other, and NDR7 is distant from the other NDR/LATS‐family PKs [16] (see also Fig. S1).…”

“…Unlike the NDR2 NDR4 NDR5 triple mutation [16], the NDR4 NDR6 NDR7 NDR8 quadruple mutation was shown to cause embryogenic lethality. NDR4, NDR6, NDR7, and NDR8 are phylogenetically closer to each other than to the other NDR/LATS‐family PKs in Arabidopsis (Fig.…”

“…S1). Because NDR2 , NDR4 , and NDR5 are more strongly expressed in pollen grains than in other tissues [16] and because the other NDR/LATS‐family PK genes are not [16] (Fig. 2), the difference in physiological roles for the NDR/LATS‐family PK genes may be due to their expression patterns.…”

“…Of these, NDR2 , NDR4 , and NDR5 are more strongly expressed in pollen grains than in leaves, roots, and other vegetative tissues and are indispensable for pollen fertility. NDR2, NDR4, and NDR5 can interact with two Arabidopsis MOB proteins, MOB1A and MOB1B, and are thought to be activated by them [16]. However, neither substrates nor physiological roles for other plant NDR/LATS‐family PKs are clear.…”

Analysis of sticky generative cell mutants reveals that suppression of callose deposition in the generative cell is necessary for generative cell internalization and differentiation in Arabidopsis

“…In Arabidopsis, Zhou et al . (2020) have proposed that the conserved Hippo signaling components, three NDR kinases (NDR2/4/5) and two MOB1 proteins (MOB1A/1B), localized in the vegetative nuclei and cytoplasm in pollen grains, function redundantly to prevent precocious pollen tube germination by suppressing callose deposition at tricellular pollen stages before pollination. This was evidenced by the normal development of both ndr2 ndr4 ndr5 triple and mob1a mob1b double mutant pollen grains up to the early tricellular pollen stage, and then the subsequent ectopic callose deposition, leading to precocious pollen tube germination in anthers before dehiscence.…”