Q. 49 Identify the CORRECT statement.
(A) Receptor-like kinases play role in gametophytic self-incompatibility in Brassicaceae
(B) Receptor-like kinases play role in sporophytic self-incompatibility in Solanaceae
(C) Ribonucleases play role in sporophytic self-incompatibility in Brassicaceae
(D) Ribonucleases play role in gametophytic self-incompatibility in Solanaceae

The correct option is (D): Ribonucleases play a role in gametophytic self-incompatibility in Solanaceae. This system is mediated by stylar S-RNases, which specifically inhibit incompatible pollen tubes.

Correct answer

The correct statement is:

(D) Ribonucleases play role in gametophytic self-incompatibility in Solanaceae.

In Solanaceae (for example, tobacco, petunia, tomato), self-incompatibility is typically gametophytic and is controlled by S-RNase (S-ribonuclease) based mechanisms in the style, which degrade RNA in self or incompatible pollen tubes and block their growth.

Concept overview: self-incompatibility systems

Self-incompatibility (SI) is a genetic mechanism that prevents self-fertilization and promotes outcrossing in flowering plants. It is generally controlled by an S-locus with multiple alleles and occurs in two main forms:

• Sporophytic SI (SSI): Pollen phenotype is determined by the diploid genotype of the parent plant (sporophyte).

• Gametophytic SI (GSI): Pollen phenotype is determined by its own haploid genotype (gametophyte).

Brassicaceae and Solanaceae represent classic, contrasting models: Brassicaceae usually have sporophytic SI mediated by receptor-like kinases, while Solanaceae typically show gametophytic SI mediated by S-RNases.

Explanation of each option

Option (A)

(A) Receptor-like kinases play role in gametophytic self-incompatibility in Brassicaceae.

• Brassicaceae (e.g., Brassica, Arabidopsis) show a predominantly sporophytic SI system, not gametophytic.

• The pistil S-determinant in Brassicaceae is an S-locus receptor kinase (SRK), a membrane-bound receptor-like kinase expressed in the stigma papillae.

• Therefore, receptor-like kinases are indeed involved, but in sporophytic, not gametophytic, self-incompatibility, making this statement incorrect.

Option (B)

(B) Receptor-like kinases play role in sporophytic self-incompatibility in Solanaceae.

• Solanaceae (e.g., Nicotiana, Petunia, Solanum) mostly exhibit gametophytic SI controlled by S-RNase in the style and pollen S-allele–specific F-box proteins, not by stigma-expressed receptor-like kinases.

• The key recognition in Solanaceae occurs inside the style tissue via ribonuclease activity, not via receptor-like kinases at the stigma surface.

• Hence, attributing sporophytic SI and receptor-like kinase involvement to Solanaceae is incorrect.

Option (C)

(C) Ribonucleases play role in sporophytic self-incompatibility in Brassicaceae.

• In Brassicaceae, the SI system is sporophytic and is mediated by the interaction between SRK (a receptor-like kinase) in the stigma and its small cysteine-rich pollen ligand (SCR/SP11) on the pollen coat.

• Ribonucleases (S-RNases) are not central components of the Brassicaceae SI system; instead, they define the pistil S-determinant in GSI systems like Solanaceae, Rosaceae, and Plantaginaceae.

• Therefore, linking ribonucleases to sporophytic SI in Brassicaceae is incorrect.

Option (D)

(D) Ribonucleases play role in gametophytic self-incompatibility in Solanaceae.

• In Solanaceae, the classic SI mechanism is gametophytic and depends on S-RNases secreted into the style, which enter growing pollen tubes.

• When pollen and pistil share the same S-allele, the S-RNase is not detoxified and degrades RNA in the pollen tube, arresting its growth and causing rejection of self pollen.

• This description matches gametophytic SI in Solanaceae perfectly, making this option correct.

Quick reference table

This table highlights why option (D) correctly associates ribonucleases with gametophytic self-incompatibility in Solanaceae, while the other options mismatch family, SI type, or molecule.