During microsporogenesis, the microsporocyte (or microspore) plasma membrane plays multiple roles in pollen wall development, including callose secretion, primexine deposition, and exine pattern determination. However, plasma membrane proteins that participate in these processes are still not well known. Here, we report that a new gene, RUPTURED POLLEN GRAIN1 (RPG1), encodes a plasma membrane protein and is required for exine pattern formation of microspores in Arabidopsis (Arabidopsis thaliana). The rpg1 mutant exhibits severely reduced male fertility with an otherwise normal phenotype, which is largely due to the postmeiotic abortion of microspores. Scanning electron microscopy examination showed that exine pattern formation in the mutant is impaired, as sporopollenin is randomly deposited on the pollen surface. Transmission electron microscopy examination further revealed that the primexine formation of mutant microspores is aberrant at the tetrad stage, which leads to defective sporopollenin deposition on microspores and the locule wall. In addition, microspore rupture and cytoplasmic leakage were evident in the rpg1 mutant, which indicates impaired cell integrity of the mutant microspores. RPG1 encodes an MtN3/saliva family protein that is integral to the plasma membrane. In situ hybridization analysis revealed that RPG1 is strongly expressed in microsporocyte (or microspores) and tapetum during male meiosis. The possible role of RPG1 in microsporogenesis is discussed.

Fatty acid desaturases play important role in plant responses to abiotic stresses. However, their exact function in plant resistance to salt stress is unknown. In this work, we provide the evidence that FAD2, an endoplasmic reticulum localized ω-6 desaturase, is required for salt tolerance in Arabidopsis. Using vacuolar and plasma membrane vesicles prepared from the leaves of wild-type (Col-0) and the loss-of-function Arabidopsis mutant, fad2, which lacks the functional FAD2, we examined the fatty acid composition and Na⁺-dependent H⁺ movements of the isolated vesicles. We observed that, when compared to Col-0, the level of vacuolar and plasma membrane polyunsaturation was lower, and the Na⁺/H⁺ exchange activity was reduced in vacuolar and plasma membrane vesicles isolated from fad2 mutant. Consistent with the reduced Na⁺/H⁺ exchange activity, fad2 accumulated more Na⁺ in the cytoplasm of root cells, and was more sensitive to salt stress during seed germination and early seedling growth, as indicated by CoroNa-Green staining, net Na⁺ efflux and salt tolerance analyses. Our results suggest that FAD2 mediated high-level vacuolar and plasma membrane fatty acid desaturation is essential for the proper function of membrane attached Na⁺/H⁺ exchangers, and thereby to maintain a low cytosolic Na⁺ concentration for salt tolerance during seed germination and early seedling growth in Arabidopsis.

In Arabidopsis thaliana, six vacuolar Na⁺/H⁺ antiporters (AtNHX1‐6) were identified. Among them, AtNHX1, 2 and 5 are functional Na⁺/H⁺ antiporters with the most abundant expression levels in seedling shoots and roots. However, the expression of AtNHX3 in Arabidopsis can only be detected by RT‐PCR, and its physiological function still remains unclear. In this work, we demonstrate that constitutive expression of AtNHX3 in sugar beet (Beta vulgaris L.) conferred augmented resistance to high salinity on transgenic plants. In the presence of 300 or 500 mm NaCl, transgenic plants showed very high potassium accumulation in the roots and storage roots. Furthermore, the transcripts of sucrose phosphate synthase (SPS), sucrose synthase (SS) and cell wall sucrose invertase (SI) genes were maintained in transgenic plants. The accumulation of soluble sugar in the storage roots of transgenic plants grown under high salt stress condition was also higher. Our results implicate that AtNHX3 is also a functional antiporter responsible for salt tolerance by mediating K⁺/H⁺ exchange in higher plants. The salt accumulation in leaves but not in the storage roots, and the increased yield of storage roots with enhanced constituent soluble sugar contents under salt stress condition demonstrate a great potential use of this gene in improving the quality and yield of crop plants.