Elevation of Pollen Mitochondrial DNA Copy Number by WHIRLY2: Altered Respiration and Pollen Tube Growth in Arabidopsis

Abstract

In plants, the copy number of the mitochondrial DNA (mtDNA) can be much lower than the number of mitochondria. The biological significance and regulatory mechanisms of this phenomenon remain poorly understood. Here, using the pollen vegetative cell, we examined the role of the Arabidopsis (Arabidopsis thaliana) mtDNA-binding protein WHIRLY2 (AtWHY2). AtWHY2 decreases during pollen development, in parallel with the rapid degradation of mtDNA; to examine the importance of this decrease, we used the pollen vegetative cell-specific promoter Lat52 to express AtWHY2. The transgenic plants (LWHY2) had very high mtDNA levels in pollen, more than 10 times more than in the wild type (ecotype Columbia-0). LWHY2 plants were fertile, morphologically normal, and set seeds; however, reciprocal crosses with heterozygous plants showed reduced transmission of LWHY2-1 through the male and slower growth of LWHY2-1 pollen tubes. We found that LWHY2-1 pollen had significantly more reactive oxygen species and less ATP compared with the wild type, indicating an effect on mitochondrial respiration. These findings reveal that AtWHY2 affects mtDNA copy number in pollen and suggest that low mtDNA copy numbers might be the normal means by which plant cells maintain mitochondrial genetic information.

Plant-Specific Preprotein and Amino Acid Transporter Proteins Are Required for tRNA Import into Mitochondria

“…Furthermore, almost 100 genes annotated as encoding proteins involved in mitochondrial transcription were increased significantly in transcript abundance in tric1tric2 plants; however, At2g34620, which is annotated as being involved in the termination of transcription, was down-regulated (Supplemental Table S3). Genes encoding a DNA polymerase (At5g15700) and Whirly2 (At1g71260) also were increased in abundance in tric1tric2 plants, with the latter shown previously to increase mitochondrial DNA copy number when expressed (Cai et al, 2015). Ninety-two genes encoding PPR proteins were significantly differentially expressed in tric1tric2 seedlings, with almost all of these being up-regulated ( Fig.…”

Changes in mitochondrial DNA levels during early embryogenesis in Torenia fournieri and Arabidopsis thaliana

“…Second, MT (partial fragment of the mitochondrial F1‐ATPase δ′ subunit) (Matsushima et al ., ) was amplified with the primers MT‐ Sal I‐S and MT‐ Nco I‐A (Table S1) from leaf complementary DNA (cDNA) and cloned into pGreen‐ProDD45 via the Sal I and Nco I sites to produce pGreen‐ProDD45‐MT . Finally, GFP–NosT was amplified from pGreen‐WHY2pro : WHY2–GFP (Cai et al ., ) with the primers GFP– Nco I‐S and NosT‐ Sac I‐A (Table S1) and cloned into pGreen‐ProDD45‐MT via the Nco I and Sac I sites to produce pGreen‐ProDD45 : MT–GFP . The vector and pSoup were imported together into Agrobacterium tumefaciens GV3101 by electroporation.…”

“…Mitochondrial DNA (mtDNA) is present in many copies per cell, and its levels change during development. For example, the mtDNA levels in somatic cells double before division to ensure that each daughter cell has an mtDNA content similar to that in the mother cell, while the number of mtDNA copies in pollen grains declines from hundreds to dozens during pollen development (Wang et al, 2010;Cai et al, 2015). The mtDNA levels are strictly regulated and closely involved in cellular functions.…”

“…The mtDNA levels are strictly regulated and closely involved in cellular functions. During pollen development in Arabidopsis thaliana, an artificial increase in mtDNA by ectopic expression of AtWHY2 leads to the accumulation of reactive oxygen species and thus reduces the growth of pollen tubes (Cai et al, 2015).…”

Boosting autophagy in sexual reproduction: a plant perspective

“…Consequently, the majority of plant mitochondrial DNA (mtDNA) is inherited from the female. The molecular basis of controlling the maternal inheritance remains largely unexplored (Cai et al, 2015;Zhou et al, 2016). In animals, several recent studies have shown the involvement of autophagy in the mitochondrial inheritance process by removal of paternal mitochondria (Politi et al, 2014;Svoboda et al, 2017;Wei et al, 2017;Palmisano & Mel endez, 2018).…”