Centromeric histone H3 protein: from basic study to plant breeding applications

Abstract

Centromere is the defining unit of a chromosome where kinetochore complex assembles and facilitates chromosome segregation. Centromeres contain unique repetitive sequences and are enriched with transposons and retrotransposons. Although how centromere is determined is still not clearly understood, binding of a key protein, namely, the Centromeric Histone H3 (CENH3) to centromeric repetitive DNA sequences has been found to be critical for the specification of centromere. Hence, centromeres are said to be epigenetically specified by CENH3. Despite considerable variation in size and sequence, CENH3 protein shows significant conservation of structure and function. CENH3 disruption or overexpression shows severe defects in spindle fiber attachment and ultimately leads to embryo lethality. Basic studies on complementation of CENH3 in Arabidopsis thaliana have led to the development of a novel method of haploid production through selective elimination of one set of parental chromosomes in the zygote. These findings have also shed new light on selective loss of chromosomes in interspecific crosses of Hordeum vulgare 9 H. bulbosum. Here, we briefly review unique features of CENH3 and discuss the new plant breeding opportunities that have emerged from the study of CENH3.

Novel technologies in doubled haploid line development

“…HvCENH3 has translation activity and can be loaded properly to the centromeres of H. vulgare , but whether HbCENH3 has translation activity is unknown. The H. bulbosum centromere has no activity during anaphase leading to chromosome elimination and H. vulgare haploid embryo development (Watts et al ., ). Centromere inactivity attributes to centromeric loss of CENH3 protein instead of uniparental transcription inactivation of CENH3 genes (Sanei et al ., ).…”

“…CENH3 consists of an N‐terminal tail region, which is highly variable even between closely related species, and a C‐terminal Histone Fold Domain (HFD), which is well conserved across species (Britt and Kuppu, ; Kuppu et al ., ; Malik and Henikoff, ). The N‐terminal tail has one alpha helix (αN), and the HFD domain has three alpha helices separated by two loop regions (α1‐L1‐α2‐L2‐α3) (Ishii et al ., ; Watts et al ., ). The CENP‐A targeting domain (CATD) composed of loop 1, and α2 is necessary for CENH3 loading to the centromere (Black et al ., ; Lermontova et al ., ; Sullivan et al ., ).…”

“…The highest haploid induction rate reached 3.6% in several AcGREEN‐tailswap‐CENH3 hemizygous lines when backcrossed as male parents. Although the haploid induction rate is too low to match maize commercial inducers, this is the first report of haploidization via CENH3‐mediated chromosome elimination in maize and will promote the generation of haploid inducers in other species (Watts et al ., ).…”

“…The possible mechanism of centromere‐mediated chromosome elimination is shown in Figure . The addition of a bulky tag and sequence changes of CENH3 can affect protein function for CENH3 reloading (Britt and Kuppu, ; Watts et al ., ). The modified centromere behaves normally, while being less competitive to wild‐type centromeres.…”

“…Chromosomes bearing modified CENH3 showed centromere reloading impair or delay leading to the loss of centromere function (Ishii et al ., ). As a result, spindle fibres failed to attach to chromosomes of haploid inducers which may be lost completely or fail in segregation, but remain in one daughter leading to development of haploids and aneuploids (Dwivedi et al ., ; Watts et al ., ).…”