Involvement of MLPK Pathway in Intraspecies Unilateral Incompatibility Regulated by a Single Locus With Stigma and Pollen Factors

Abstract

Plants have evolved many systems to prevent undesirable fertilization. Among these, incompatibility is a well-organized system in which pollen germination or pollen tube growth is inhibited in pistils. We previously found that a novel one-way pollen–stigma incompatibility response [unilateral incompatibility (UI)] occurred between two self-incompatible Brassica rapa plants, a Turkish line, and a Japanese cultivated hybrid variety, “Osome.” Pollen from the Turkish line is rejected on the stigma of the Osome line, but the reverse cross is compatible; such a UI phenotype closely resembles self-incompatibility (SI). The pollen factor of this UI has been genetically explained by a single locus which is different from the S-locus. In this study, we performed further genetic analyses of this intraspecies UI and showed that the stigma factor was also controlled by a single locus, and we named the loci corresponding to the stigma and pollen factors of the intraspecies UI, stigmatic unilateral incompatibility (SUI), and pollen unilateral incompatibility (PUI) loci, respectively. Interestingly, segregation analyses of SUI and PUI indicated that they are closely linked to each other and behave as a single unit. To investigate the effect of an SI-related gene, MLPK in this UI, we produced segregation lines for SUI and mlpk. A distorted segregation ratio of SUI phenotype in an mlpk background indicated involvement of MLPK in SUI, suggesting the existence of an MLPK-dependent novel pollen–stigma recognition mechanism.

Genetic Diversity of Genes Controlling Unilateral Incompatibility in Japanese Cultivars of Chinese Cabbage

“…The physiological pollen-rejection phenotype of the intraspecies UI is similar to that of SI and is consistent with the involvement of M-locus protein kinase (MLPK) in UI, which may function in SRK-mediated SI signal transduction [15,16]. It is noteworthy that the incompatibility response of UI is almost as strong as in the rigid SI phenotype in B. rapa.…”

“…To verify the stigma-side UI phenotype of the Japanese cultivars of Chinese cabbage, stigmas of 47 cultivars were crossed with the pollen from the Turkish line (S 24 t, S 40 t, or S 21 t) possessing PUI1-1/PUI1-1 with crossing combinations of different S-haplotypes for discriminating the UI phenotype from the SI phenotype (S 21 t was produced for this study) [16]. Among the 47 cultivars, 85% (40 cultivars) had the incompatibility (UI) phenotype to the Turkish pollen (Table 1).…”

Pollen-Pistil Interactions and Their Role in Mate Selection

“…In Brassicaceae, signaling initiates the rejection response in the stigma papillar cell, while in Papaver, it is the pollen tube that responds to signaling. As the rejection response is induced in these systems, loss-of-function mutations in either the pollen-or pistil-side genes can cause SC, and, with some notable exceptions (Takada et al, 2013), the default for intraspecific pollination is compatibility. Iwano and Takayama (2012) refer to Papaver and Brassicaceae SI as self-recognition systems in the sense that the pollen-and pistil-expressed protein pair, encoded in a common (i.e.…”

Self-incompatibility in Brassicaceae crops: lessons for interspecific incompatibility

“…In the Brassicaceae, interspecific incompatibility has been observed in interspecific pollinations between B. rapa and B. oleracea . In addition, one case of unusual unilateral intraspecific incompatibility was reported in B. rapa ( Takada et al 2013 ), which will not be discussed further. In all cases of interspecific unilateral incompatibility that have been examined, only cytological and genetic analyses have been performed, and the molecular basis of pollen inhibition is not known.…”