S RNase and Interspecific Pollen Rejection in the Genus Nicotiana: Multiple Pollen-Rejection Pathways Contribute to...

Area of Science:

• Plant reproductive biology
• Genetics
• Molecular biology

Background:

• Self-incompatibility (SI) in plants prevents self-pollination via the S locus, promoting outcrossing.
• Interspecific crosses between SI and self-compatible (SC) species often exhibit unilateral incompatibility (SI x SC rule).
• Exceptions to the SI x SC rule have raised questions about the S locus' role in interspecific pollen rejection.

Purpose of the Study:

• To investigate the role of the S locus in interspecific pollen rejection.
• To clarify the mechanisms underlying unilateral incompatibility between Nicotiana species.

Main Methods:

• Transformed Nicotiana species and hybrids with SA2 or SC10 RNase genes from SI N. alata.
• Tested compatibility phenotypes of transgenic plants using pollen from three SC Nicotiana species.
• Analyzed S RNase-dependent and independent pollen rejection mechanisms.

Main Results:

• S RNase was implicated in rejecting pollen from all three tested SC species.
• Rejection of N. plumbaginifolia pollen required both S RNase and other genetic factors from N. alata.
• Rejection of N. glutinosa and N. tabacum pollen was S RNase-dependent but did not require additional factors; N. alata also uses an S RNase-independent mechanism for these species.

Conclusions:

• The S locus is implicated in interspecific pollen rejection across the studied Nicotiana systems.
• Multiple genetic mechanisms, including S RNase-dependent and independent pathways, contribute to interspecific pollen rejection.
• The findings provide a clearer understanding of the genetic basis of reproductive isolation between plant species.