40. Members of the WUSCHEL RELATED HOMEOBOX (WOX) transcription factor family play an important role during zygote elongation and division in Arabidopsis. Following are certain statements regarding the expression of different members of WOX gene family during zygote
    elongation.
    (A) WOX2 and WOX8 are present in both the egg cell and the zygote.
    (B) WOX2 is present in the apical and basal cell.
    (C) WOX8 along with WOX9 regulates the development of basal lineage.
    (D) WOX8 and WOX9 are directly activated in the zygote by the transcription factor WRKY2.
    Which one of the following options represents combination of all correct statements?
    (1) A, B and C (2) A, B and D
    (3) A, C and D (4) B, C and D

The combination of all correct statements regarding the expression of WOX gene family members during zygote elongation in Arabidopsis is:

(3) A, C and D

Explanation:

• (A) WOX2 and WOX8 are present in both the egg cell and the zygote — Correct. Both WOX2 and WOX8 transcripts are maternally deposited in the egg cell and continue to be expressed in the zygote, playing roles in early development.​

• (B) WOX2 is present in both the apical and basal cell — Incorrect. WOX2 expression is largely restricted to the apical cell after the zygotic division, which forms the embryo proper; it is not significantly expressed in the basal cell lineage.​

• (C) WOX8 along with WOX9 regulates the development of the basal lineage — Correct. WOX8 and WOX9 act redundantly to promote basal cell lineage development, which will give rise to the suspensor and root pole.​

• (D) WOX8 and WOX9 are directly activated in the zygote by the transcription factor WRKY2 — Correct. WRKY2 transcription factor regulates transcription of WOX8 and presumably WOX9 in the zygote, crucial for zygote polarization and asymmetric division.​

Introduction

In Arabidopsis embryogenesis, members of the WUSCHEL RELATED HOMEOBOX (WOX) gene family, including WOX2, WOX8, and WOX9, coordinate early zygote elongation and division. These genes establish apical-basal polarity and lineage specification during the transition from fertilized egg to multicellular embryo. The WRKY2 transcription factor plays a critical role in activating WOX8 and WOX9, linking signaling pathways to transcriptional regulation of embryo development.

Expression Patterns and Roles of WOX Genes

• WOX2 is maternally inherited and initially present in both egg cell and zygote but becomes restricted to the apical cell post first division, which forms embryo proper.​

• WOX8 and WOX9 are expressed in the egg cell and basal lineage including suspensor formation, functioning redundantly to regulate basal cell fate and development.​

• These gene expressions delineate the apical-basal axis, crucial for embryo polarity and subsequent morphogenesis.​

Role of WRKY2 in WOX Gene Regulation

• WRKY2 directly activates WOX8 transcription in the zygote, integrating paternal and maternal signals to regulate zygote elongation and asymmetry.​

• Mutations in WRKY2 result in aberrant zygote division and affect WOX8 expression, underscoring its regulatory role.​

• WRKY2-WOX8/9 interaction is part of the early transcriptional network patterning the embryo.​

Summary Table: WOX Genes and WRKY2 in Arabidopsis Zygote

Conclusion

Statements A, C, and D accurately describe the roles and expression of WOX2, WOX8, WOX9, and WRKY2 in Arabidopsis zygote elongation, polarity, and basal lineage development. Statement B is incorrect as WOX2 is not expressed in the basal cell.