Methionine adenosyltransferase MAT3 positively regulates pear pollen tube growth, possibly through interaction with pectin lyase-like protein PLL1.

Abstract

Methionine adenosyltransferase (MAT) is the only enzyme that synthesises S-adenosylmethionine (SAM) from ATP and methionine in organisms. While MAT has been extensively studied in plant development and responses to abiotic stress, its role in plant fertilization, particularly in pear pollen tube growth, has been scarcely researched. Here, we demonstrate that the homologous gene of AtMAT3 in pear, PbrMAT3, is positively involved in pear pollen tube elongation. PbrMAT3 is predominantly expressed in pear pollen. Transient knockdown of PbrMAT3 inhibits pollen tube growth. Ethionine, a toxic methionine analogue, suppressed pollen tube growth in control samples but had no inhibitory effect on PbrMAT3-knockdown pollen tubes, suggesting increased methionine accumulation in the latter. However, this accumulation is not responsible for the observed growth inhibition. PbrMAT3 interacts with a pectin lyase-like protein, PbrPLL1, both in vivo and in vitro. Transient knockdown of PbrPLL1 promotes pollen tube growth, suggesting its negative role in pear pollen tube elongation. Additionally, the pectate lyase activity of the pear pollen tube was increased when PbrMAT3 was knocked down. Thus, the inhibition of pollen tube growth due to PbrMAT3 knockdown is not caused by methionine accumulation but may be mediated by PbrPLL1. This study provides new insight into the relationship between S-adenosylmethionine synthesis and pollen tube growth.