NaTrxh is an essential protein for pollen rejection in <i>Nicotiana</i> by increasing S‐RNase activity
María Daniela Torres-Rodríguez, Yuridia Cruz‐Zamora, Javier Andrés Juárez‐Díaz, Brian Mooney, Bruce McClure, Felipe Cruz‐García
Abstract
Summary In self‐incompatible Solanaceae, the pistil protein S‐RNase contributes to S ‐specific pollen rejection in conspecific crosses, as well as to rejecting pollen from foreign species or whole clades. However, S‐RNase alone is not sufficient for either type of pollen rejection. We describe a thioredoxin (Trx) type h from Nicotiana alata , NaTrxh, which interacts with and reduces S‐RNase in vitro . Here, we show that expressing a redox‐inactive mutant, NaTrxh SS , suppresses both S ‐specific pollen rejection and rejection of pollen from Nicotiana plumbaginifolia . Biochemical experiments provide evidence that NaTrxh specifically reduces the Cys 155 ‐Cys 185 disulphide bond of S C10 ‐Rnase, resulting in a significant increase of its ribonuclease activity. This reduction and increase in S‐RNase activity by NaTrxh helps to explain why S‐RNase alone could be insufficient for pollen rejection.